Format specifies type 'char ' but the argument has type 'char ()[12]'如何解决

啊这是谁 2019-11-10 06:34:47

程序可以运行，但是会有提醒格式不对，有人能帮忙解决一下吗？刚刚学C语言真的问了很多白痴问题……谢谢！！

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liups 2019-11-10

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引用 1 楼 SuperDay 的回复:

不要用&符号，order本来就是数组首地址

wowpH 2019-11-10

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参考：https://baike.baidu.com/item/scanf/10773316?fr=aladdin#5_1 解决了就结贴，不要点赞。 CSDN论坛新手指南

铖邑 2019-11-10

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不要用&符号，order本来就是数组首地址

Table of Contents Header Files The #define Guard Header File Dependencies Inline Functions The -inl.h Files Function Parameter Ordering Names and Order of Includes Scoping Namespaces Nested Classes Nonmember, Static Member, and Global Functions Local Variables Static and Global Variables Classes Doing Work in Constructors Default Constructors Explicit Constructors Copy Constructors Structs vs. Classes Inheritance Multiple Inheritance Interfaces Operator Overloading Access Control Declaration Order Write Short Functions Google-Specific Magic Smart Pointers cpplint Other C++ Features Reference Arguments Function Overloading Default Arguments Variable-Length Arrays and alloca() Friends Exceptions Run-Time Type Information (RTTI) Casting Streams Preincrement and Predecrement Use of const Integer Types 64-bit Portability Preprocessor Macros 0 and NULL sizeof Boost C++0x Naming General Naming Rules File Names Type Names Variable Names Constant Names Function Names Namespace Names Enumerator Names Macro Names Exceptions to Naming Rules Comments Comment Style File Comments Class Comments Function Comments Variable Comments Implementation Comments Punctuation, Spelling and Grammar TODO Comments Deprecation Comments Formatting Line Length Non-ASCII Characters Spaces vs. Tabs Function Declarations and Definitions Function Calls Conditionals Loops and Switch Statements Pointer and Reference Expressions Boolean Expressions Return Values Variable and Array Initialization Preprocessor Directives Class Format Constructor Initializer Lists Namespace Formatting Horizontal Whitespace Vertical Whitespace Exceptions to the Rules Existing Non-conformant Code Windows Code Important Note Displaying Hidden Details in this Guide link ▶This style guide contains many details that are initially hidden from view. They are marked by the triangle icon, which you see here on your left. Click it now. You should see "Hooray" appear below. Hooray! Now you know you can expand points to get more details. Alternatively, there's an "expand all" at the top of this document. Background C++ is the main development language used by many of Google's open-source projects. As every C++ programmer knows, the language has many powerful features, but this power brings with it complexity, which in turn can make code more bug-prone and harder to read and maintain. The goal of this guide is to manage this complexity by describing in detail the dos and don'ts of writing C++ code. These rules exist to keep the code base manageable while still allowing coders to use C++ language features productively. Style, also known as readability, is what we call the conventions that govern our C++ code. The term Style is a bit of a misnomer, since these conventions cover far more than just source file formatting. One way in which we keep the code base manageable is by enforcing consistency. It is very important that any programmer be able to look at another's code and quickly understand it. Maintaining a uniform style and following conventions means that we can more easily use "pattern-matching" to infer what various symbols are and what invariants are true about them. Creating common, required idioms and patterns makes code much easier to understand. In some cases there might be good arguments for changing certain style rules, but we nonetheless keep things as they are in order to preserve consistency. Another issue this guide addresses is that of C++ feature bloat. C++ is a huge language with many advanced features. In some cases we constrain, or even ban, use of certain features. We do this to keep code simple and to avoid the various common errors and problems that these features can cause. This guide lists these features and explains why their use is restricted. Open-source projects developed by Google conform to the requirements in this guide. Note that this guide is not a C++ tutorial: we assume that the reader is familiar with the language. Header Files In general, every .cc file should have an associated .h file. There are some common exceptions, such as unittests and small .cc files containing just a main() function. Correct use of header files can make a huge difference to the readability, size and performance of your code. The following rules will guide you through the various pitfalls of using header files. The #define Guard link ▶All header files should have #define guards to prevent multiple inclusion. The format of the symbol name should be ___H_. To guarantee uniqueness, they should be based on the full path in a project's source tree. For example, the file foo/src/bar/baz.h in project foo should have the following guard: #ifndef FOO_BAR_BAZ_H_ #define FOO_BAR_BAZ_H_ ... #endif // FOO_BAR_BAZ_H_ Header File Dependencies link ▶Don't use an #include when a forward declaration would suffice. When you include a header file you introduce a dependency that will cause your code to be recompiled whenever the header file changes. If your header file includes other header files, any change to those files will cause any code that includes your header to be recompiled. Therefore, we prefer to minimize includes, particularly includes of header files in other header files. You can significantly minimize the number of header files you need to include in your own header files by using forward declarations. For example, if your header file uses the File class in ways that do not require access to the declaration of the File class, your header file can just forward declare class File; instead of having to #include "file/base/file.h". How can we use a class Foo in a header file without access to its definition? We can declare data members of type Foo* or Foo&. We can declare (but not define) functions with arguments, and/or return values, of type Foo. (One exception is if an argument Foo or const Foo& has a non-explicit, one-argument constructor, in which case we need the full definition to support automatic type conversion.) We can declare static data members of type Foo. This is because static data members are defined outside the class definition. On the other hand, you must include the header file for Foo if your class subclasses Foo or has a data member of type Foo. Sometimes it makes sense to have pointer (or better, scoped_ptr) members instead of object members. However, this complicates code readability and imposes a performance penalty, so avoid doing this transformation if the only purpose is to minimize includes in header files. Of course, .cc files typically do require the definitions of the classes they use, and usually have to include several header files. Note: If you use a symbol Foo in your source file, you should bring in a definition for Foo yourself, either via an #include or via a forward declaration. Do not depend on the symbol being brought in transitively via headers not directly included. One exception is if Foo is used in myfile.cc, it's ok to #include (or forward-declare) Foo in myfile.h, instead of myfile.cc. Inline Functions link ▶Define functions inline only when they are small, say, 10 lines or less. Definition: You can declare functions in a way that allows the compiler to expand them inline rather than calling them through the usual function call mechanism. Pros: Inlining a function can generate more efficient object code, as long as the inlined function is small. Feel free to inline accessors and mutators, and other short, performance-critical functions. Cons: Overuse of inlining can actually make programs slower. Depending on a function's size, inlining it can cause the code size to increase or decrease. Inlining a very small accessor function will usually decrease code size while inlining a very large function can dramatically increase code size. On modern processors smaller code usually runs faster due to better use of the instruction cache. Decision: A decent rule of thumb is to not inline a function if it is more than 10 lines long. Beware of destructors, which are often longer than they appear because of implicit member- and base-destructor calls! Another useful rule of thumb: it's typically not cost effective to inline functions with loops or switch statements (unless, in the common case, the loop or switch statement is never executed). It is important to know that functions are not always inlined even if they are declared as such; for example, virtual and recursive functions are not normally inlined. Usually recursive functions should not be inline. The main reason for making a virtual function inline is to place its definition in the class, either for convenience or to document its behavior, e.g., for accessors and mutators. The -inl.h Files link ▶You may use file names with a -inl.h suffix to define complex inline functions when needed. The definition of an inline function needs to be in a header file, so that the compiler has the definition available for inlining at the call sites. However, implementation code properly belongs in .cc files, and we do not like to have much actual code in .h files unless there is a readability or performance advantage. If an inline function definition is short, with very little, if any, logic in it, you should put the code in your .h file. For example, accessors and mutators should certainly be inside a class definition. More complex inline functions may also be put in a .h file for the convenience of the implementer and callers, though if this makes the .h file too unwieldy you can instead put that code in a separate -inl.h file. This separates the implementation from the class definition, while still allowing the implementation to be included where necessary. Another use of -inl.h files is for definitions of function templates. This can be used to keep your template definitions easy to read. Do not forget that a -inl.h file requires a #define guard just like any other header file. Function Parameter Ordering link ▶When defining a function, parameter order is: inputs, then outputs. Parameters to C/C++ functions are either input to the function, output from the function, or both. Input parameters are usually values or const references, while output and input/output parameters will be non-const pointers. When ordering function parameters, put all input-only parameters before any output parameters. In particular, do not add new parameters to the end of the function just because they are new; place new input-only parameters before the output parameters. This is not a hard-and-fast rule. Parameters that are both input and output (often classes/structs) muddy the waters, and, as always, consistency with related functions may require you to bend the rule. Names and Order of Includes link ▶Use standard order for readability and to avoid hidden dependencies: C library, C++ library, other libraries' .h, your project's .h. All of a project's header files should be listed as descentants of the project's source directory without use of UNIX directory shortcuts . (the current directory) or .. (the parent directory). For example, google-awesome-project/src/base/logging.h should be included as #include "base/logging.h" In dir/foo.cc, whose main purpose is to implement or test the stuff in dir2/foo2.h, order your includes as follows: dir2/foo2.h (preferred location — see details below). C system files. C++ system files. Other libraries' .h files. Your project's .h files. The preferred ordering reduces hidden dependencies. We want every header file to be compilable on its own. The easiest way to achieve this is to make sure that every one of them is the first .h file #included in some .cc. dir/foo.cc and dir2/foo2.h are often in the same directory (e.g. base/basictypes_test.cc and base/basictypes.h), but can be in different directories too. Within each section it is nice to order the includes alphabetically. For example, the includes in google-awesome-project/src/foo/internal/fooserver.cc might look like this: #include "foo/public/fooserver.h" // Preferred location. #include #include #include #include #include "base/basictypes.h" #include "base/commandlineflags.h" #include "foo/public/bar.h" Scoping Namespaces link ▶Unnamed namespaces in .cc files are encouraged. With named namespaces, choose the name based on the project, and possibly its path. Do not use a using-directive. Definition: Namespaces subdivide the global scope into distinct, named scopes, and so are useful for preventing name collisions in the global scope. Pros: Namespaces provide a (hierarchical) axis of naming, in addition to the (also hierarchical) name axis provided by classes. For example, if two different projects have a class Foo in the global scope, these symbols may collide at compile time or at runtime. If each project places their code in a namespace, project1::Foo and project2::Foo are now distinct symbols that do not collide. Cons: Namespaces can be confusing, because they provide an additional (hierarchical) axis of naming, in addition to the (also hierarchical) name axis provided by classes. Use of unnamed spaces in header files can easily cause violations of the C++ One Definition Rule (ODR). Decision: Use namespaces according to the policy described below. Unnamed Namespaces Unnamed namespaces are allowed and even encouraged in .cc files, to avoid runtime naming conflicts: namespace { // This is in a .cc file. // The content of a namespace is not indented enum { kUnused, kEOF, kError }; // Commonly used tokens. bool AtEof() { return pos_ == kEOF; } // Uses our namespace's EOF. } // namespace However, file-scope declarations that are associated with a particular class may be declared in that class as types, static data members or static member functions rather than as members of an unnamed namespace. Terminate the unnamed namespace as shown, with a comment // namespace. Do not use unnamed namespaces in .h files. Named Namespaces Named namespaces should be used as follows: Namespaces wrap the entire source file after includes, gflags definitions/declarations, and forward declarations of classes from other namespaces: // In the .h file namespace mynamespace { // All declarations are within the namespace scope. // Notice the lack of indentation. class MyClass { public: ... void Foo(); }; } // namespace mynamespace // In the .cc file namespace mynamespace { // Definition of functions is within scope of the namespace. void MyClass::Foo() { ... } } // namespace mynamespace The typical .cc file might have more complex detail, including the need to reference classes in other namespaces. #include "a.h" DEFINE_bool(someflag, false, "dummy flag"); class C; // Forward declaration of class C in the global namespace. namespace a { class A; } // Forward declaration of a::A. namespace b { ...code for b... // Code goes against the left margin. } // namespace b Do not declare anything in namespace std, not even forward declarations of standard library classes. Declaring entities in namespace std is undefined behavior, i.e., not portable. To declare entities from the standard library, include the appropriate header file. You may not use a using-directive to make all names from a namespace available. // Forbidden -- This pollutes the namespace. using namespace foo; You may use a using-declaration anywhere in a .cc file, and in functions, methods or classes in .h files. // OK in .cc files. // Must be in a function, method or class in .h files. using ::foo::bar; Namespace aliases are allowed anywhere in a .cc file, anywhere inside the named namespace that wraps an entire .h file, and in functions and methods. // Shorten access to some commonly used names in .cc files. namespace fbz = ::foo::bar::baz; // Shorten access to some commonly used names (in a .h file). namespace librarian { // The following alias is available to all files including // this header (in namespace librarian): // alias names should therefore be chosen consistently // within a project. namespace pd_s = ::pipeline_diagnostics::sidetable; inline void my_inline_function() { // namespace alias local to a function (or method). namespace fbz = ::foo::bar::baz; ... } } // namespace librarian Note that an alias in a .h file is visible to everyone #including that file, so public headers (those available outside a project) and headers transitively #included by them, should avoid defining aliases, as part of the general goal of keeping public APIs as small as possible. Nested Classes link ▶Although you may use public nested classes when they are part of an interface, consider a namespace to keep declarations out of the global scope. Definition: A class can define another class within it; this is also called a member class. class Foo { private: // Bar is a member class, nested within Foo. class Bar { ... }; }; Pros: This is useful when the nested (or member) class is only used by the enclosing class; making it a member puts it in the enclosing class scope rather than polluting the outer scope with the class name. Nested classes can be forward declared within the enclosing class and then defined in the .cc file to avoid including the nested class definition in the enclosing class declaration, since the nested class definition is usually only relevant to the implementation. Cons: Nested classes can be forward-declared only within the definition of the enclosing class. Thus, any header file manipulating a Foo::Bar* pointer will have to include the full class declaration for Foo. Decision: Do not make nested classes public unless they are actually part of the interface, e.g., a class that holds a set of options for some method. Nonmember, Static Member, and Global Functions link ▶Prefer nonmember functions within a namespace or static member functions to global functions; use completely global functions rarely. Pros: Nonmember and static member functions can be useful in some situations. Putting nonmember functions in a namespace avoids polluting the global namespace. Cons: Nonmember and static member functions may make more sense as members of a new class, especially if they access external resources or have significant dependencies. Decision: Sometimes it is useful, or even necessary, to define a function not bound to a class instance. Such a function can be either a static member or a nonmember function. Nonmember functions should not depend on external variables, and should nearly always exist in a namespace. Rather than creating classes only to group static member functions which do not share static data, use namespaces instead. Functions defined in the same compilation unit as production classes may introduce unnecessary coupling and link-time dependencies when directly called from other compilation units; static member functions are particularly susceptible to this. Consider extracting a new class, or placing the functions in a namespace possibly in a separate library. If you must define a nonmember function and it is only needed in its .cc file, use an unnamed namespace or static linkage (eg static int Foo() {...}) to limit its scope. Local Variables link ▶Place a function's variables in the narrowest scope possible, and initialize variables in the declaration. C++ allows you to declare variables anywhere in a function. We encourage you to declare them in as local a scope as possible, and as close to the first use as possible. This makes it easier for the reader to find the declaration and see what type the variable is and what it was initialized to. In particular, initialization should be used instead of declaration and assignment, e.g. int i; i = f(); // Bad -- initialization separate from declaration. int j = g(); // Good -- declaration has initialization. Note that gcc implements for (int i = 0; i < 10; ++i) correctly (the scope of i is only the scope of the for loop), so you can then reuse i in another for loop in the same scope. It also correctly scopes declarations in if and while statements, e.g. while (const char* p = strchr(str, '/')) str = p + 1; There is one caveat: if the variable is an object, its constructor is invoked every time it enters scope and is created, and its destructor is invoked every time it goes out of scope. // Inefficient implementation: for (int i = 0; i < 1000000; ++i) { Foo f; // My ctor and dtor get called 1000000 times each. f.DoSomething(i); } It may be more efficient to declare such a variable used in a loop outside that loop: Foo f; // My ctor and dtor get called once each. for (int i = 0; i < 1000000; ++i) { f.DoSomething(i); } Static and Global Variables link ▶Static or global variables of class type are forbidden: they cause hard-to-find bugs due to indeterminate order of construction and destruction. Objects with static storage duration, including global variables, static variables, static class member variables, and function static variables, must be Plain Old Data (POD): only ints, chars, floats, or pointers, or arrays/structs of POD. The order in which class constructors and initializers for static variables are called is only partially specified in C++ and can even change from build to build, which can cause bugs that are difficult to find. Therefore in addition to banning globals of class type, we do not allow static POD variables to be initialized with the result of a function, unless that function (such as getenv(), or getpid()) does not itself depend on any other globals. Likewise, the order in which destructors are called is defined to be the reverse of the order in which the constructors were called. Since constructor order is indeterminate, so is destructor order. For example, at program-end time a static variable might have been destroyed, but code still running -- perhaps in another thread -- tries to access it and fails. Or the destructor for a static 'string' variable might be run prior to the destructor for another variable that contains a reference to that string. As a result we only allow static variables to contain POD data. This rule completely disallows vector (use C arrays instead), or string (use const char []). If you need a static or global variable of a class type, consider initializing a pointer (which will never be freed), from either your main() function or from pthread_once(). Note that this must be a raw pointer, not a "smart" pointer, since the smart pointer's destructor will have the order-of-destructor issue that we are trying to avoid. Classes Classes are the fundamental unit of code in C++. Naturally, we use them extensively. This section lists the main dos and don'ts you should follow when writing a class. Doing Work in Constructors link ▶In general, constructors should merely set member variables to their initial values. Any complex initialization should go in an explicit Init() method. Definition: It is possible to perform initialization in the body of the constructor. Pros: Convenience in typing. No need to worry about whether the class has been initialized or not. Cons: The problems with doing work in constructors are: There is no easy way for constructors to signal errors, short of using exceptions (which are forbidden). If the work fails, we now have an object whose initialization code failed, so it may be an indeterminate state. If the work calls virtual functions, these calls will not get dispatched to the subclass implementations. Future modification to your class can quietly introduce this problem even if your class is not currently subclassed, causing much confusion. If someone creates a global variable of this type (which is against the rules, but still), the constructor code will be called before main(), possibly breaking some implicit assumptions in the constructor code. For instance, gflags will not yet have been initialized. Decision: If your object requires non-trivial initialization, consider having an explicit Init() method. In particular, constructors should not call virtual functions, attempt to raise errors, access potentially uninitialized global variables, etc. Default Constructors link ▶You must define a default constructor if your class defines member variables and has no other constructors. Otherwise the compiler will do it for you, badly. Definition: The default constructor is called when we new a class object with no arguments. It is always called when calling new[] (for arrays). Pros: Initializing structures by default, to hold "impossible" values, makes debugging much easier. Cons: Extra work for you, the code writer. Decision: If your class defines member variables and has no other constructors you must define a default constructor (one that takes no arguments). It should preferably initialize the object in such a way that its internal state is consistent and valid. The reason for this is that if you have no other constructors and do not define a default constructor, the compiler will generate one for you. This compiler generated constructor may not initialize your object sensibly. If your class inherits from an existing class but you add no new member variables, you are not required to have a default constructor. Explicit Constructors link ▶Use the C++ keyword explicit for constructors with one argument. Definition: Normally, if a constructor takes one argument, it can be used as a conversion. For instance, if you define Foo::Foo(string name) and then pass a string to a function that expects a Foo, the constructor will be called to convert the string into a Foo and will pass the Foo to your function for you. This can be convenient but is also a source of trouble when things get converted and new objects created without you meaning them to. Declaring a constructor explicit prevents it from being invoked implicitly as a conversion. Pros: Avoids undesirable conversions. Cons: None. Decision: We require all single argument constructors to be explicit. Always put explicit in front of one-argument constructors in the class definition: explicit Foo(string name); The exception is copy constructors, which, in the rare cases when we allow them, should probably not be explicit. Classes that are intended to be transparent wrappers around other classes are also exceptions. Such exceptions should be clearly marked with comments. Copy Constructors link ▶Provide a copy constructor and assignment operator only when necessary. Otherwise, disable them with DISALLOW_COPY_AND_ASSIGN. Definition: The copy constructor and assignment operator are used to create copies of objects. The copy constructor is implicitly invoked by the compiler in some situations, e.g. passing objects by value. Pros: Copy constructors make it easy to copy objects. STL containers require that all contents be copyable and assignable. Copy constructors can be more efficient than CopyFrom()-style workarounds because they combine construction with copying, the compiler can elide them in some contexts, and they make it easier to avoid heap allocation. Cons: Implicit copying of objects in C++ is a rich source of bugs and of performance problems. It also reduces readability, as it becomes hard to track which objects are being passed around by value as opposed to by reference, and therefore where changes to an object are reflected. Decision: Few classes need to be copyable. Most should have neither a copy constructor nor an assignment operator. In many situations, a pointer or reference will work just as well as a copied value, with better performance. For example, you can pass function parameters by reference or pointer instead of by value, and you can store pointers rather than objects in an STL container. If your class needs to be copyable, prefer providing a copy method, such as CopyFrom() or Clone(), rather than a copy constructor, because such methods cannot be invoked implicitly. If a copy method is insufficient in your situation (e.g. for performance reasons, or because your class needs to be stored by value in an STL container), provide both a copy constructor and assignment operator. If your class does not need a copy constructor or assignment operator, you must explicitly disable them. To do so, add dummy declarations for the copy constructor and assignment operator in the private: section of your class, but do not provide any corresponding definition (so that any attempt to use them results in a link error). For convenience, a DISALLOW_COPY_AND_ASSIGN macro can be used: // A macro to disallow the copy constructor and operator= functions // This should be used in the private: declarations for a class #define DISALLOW_COPY_AND_ASSIGN(TypeName) \ TypeName(const TypeName&); \ void operator=(const TypeName&) Then, in class Foo: class Foo { public: Foo(int f); ~Foo(); private: DISALLOW_COPY_AND_ASSIGN(Foo); }; Structs vs. Classes link ▶Use a struct only for passive objects that carry data; everything else is a class. The struct and class keywords behave almost identically in C++. We add our own semantic meanings to each keyword, so you should use the appropriate keyword for the data-type you're defining. structs should be used for passive objects that carry data, and may have associated constants, but lack any functionality other than access/setting the data members. The accessing/setting of fields is done by directly accessing the fields rather than through method invocations. Methods should not provide behavior but should only be used to set up the data members, e.g., constructor, destructor, Initialize(), Reset(), Validate(). If more functionality is required, a class is more appropriate. If in doubt, make it a class. For consistency with STL, you can use struct instead of class for functors and traits. Note that member variables in structs and classes have different naming rules. Inheritance link ▶Composition is often more appropriate than inheritance. When using inheritance, make it public. Definition: When a sub-class inherits from a base class, it includes the definitions of all the data and operations that the parent base class defines. In practice, inheritance is used in two major ways in C++: implementation inheritance, in which actual code is inherited by the child, and interface inheritance, in which only method names are inherited. Pros: Implementation inheritance reduces code size by re-using the base class code as it specializes an existing type. Because inheritance is a compile-time declaration, you and the compiler can understand the operation and detect errors. Interface inheritance can be used to programmatically enforce that a class expose a particular API. Again, the compiler can detect errors, in this case, when a class does not define a necessary method of the API. Cons: For implementation inheritance, because the code implementing a sub-class is spread between the base and the sub-class, it can be more difficult to understand an implementation. The sub-class cannot override functions that are not virtual, so the sub-class cannot change implementation. The base class may also define some data members, so that specifies physical layout of the base class. Decision: All inheritance should be public. If you want to do private inheritance, you should be including an instance of the base class as a member instead. Do not overuse implementation inheritance. Composition is often more appropriate. Try to restrict use of inheritance to the "is-a" case: Bar subclasses Foo if it can reasonably be said that Bar "is a kind of" Foo. Make your destructor virtual if necessary. If your class has virtual methods, its destructor should be virtual. Limit the use of protected to those member functions that might need to be accessed from subclasses. Note that data members should be private. When redefining an inherited virtual function, explicitly declare it virtual in the declaration of the derived class. Rationale: If virtual is omitted, the reader has to check all ancestors of the class in question to determine if the function is virtual or not. Multiple Inheritance link ▶Only very rarely is multiple implementation inheritance actually useful. We allow multiple inheritance only when at most one of the base classes has an implementation; all other base classes must be pure interface classes tagged with the Interface suffix. Definition: Multiple inheritance allows a sub-class to have more than one base class. We distinguish between base classes that are pure interfaces and those that have an implementation. Pros: Multiple implementation inheritance may let you re-use even more code than single inheritance (see Inheritance). Cons: Only very rarely is multiple implementation inheritance actually useful. When multiple implementation inheritance seems like the solution, you can usually find a different, more explicit, and cleaner solution. Decision: Multiple inheritance is allowed only when all superclasses, with the possible exception of the first one, are pure interfaces. In order to ensure that they remain pure interfaces, they must end with the Interface suffix. Note: There is an exception to this rule on Windows. Interfaces link ▶Classes that satisfy certain conditions are allowed, but not required, to end with an Interface suffix. Definition: A class is a pure interface if it meets the following requirements: It has only public pure virtual ("= 0") methods and static methods (but see below for destructor). It may not have non-static data members. It need not have any constructors defined. If a constructor is provided, it must take no arguments and it must be protected. If it is a subclass, it may only be derived from classes that satisfy these conditions and are tagged with the Interface suffix. An interface class can never be directly instantiated because of the pure virtual method(s) it declares. To make sure all implementations of the interface can be destroyed correctly, they must also declare a virtual destructor (in an exception to the first rule, this should not be pure). See Stroustrup, The C++ Programming Language, 3rd edition, section 12.4 for details. Pros: Tagging a class with the Interface suffix lets others know that they must not add implemented methods or non static data members. This is particularly important in the case of multiple inheritance. Additionally, the interface concept is already well-understood by Java programmers. Cons: The Interface suffix lengthens the class name, which can make it harder to read and understand. Also, the interface property may be considered an implementation detail that shouldn't be exposed to clients. Decision: A class may end with Interface only if it meets the above requirements. We do not require the converse, however: classes that meet the above requirements are not required to end with Interface. Operator Overloading link ▶Do not overload operators except in rare, special circumstances. Definition: A class can define that operators such as + and / operate on the class as if it were a built-in type. Pros: Can make code appear more intuitive because a class will behave in the same way as built-in types (such as int). Overloaded operators are more playful names for functions that are less-colorfully named, such as Equals() or Add(). For some template functions to work correctly, you may need to define operators. Cons: While operator overloading can make code more intuitive, it has several drawbacks: It can fool our intuition into thinking that expensive operations are cheap, built-in operations. It is much harder to find the call sites for overloaded operators. Searching for Equals() is much easier than searching for relevant invocations of ==. Some operators work on pointers too, making it easy to introduce bugs. Foo + 4 may do one thing, while &Foo + 4 does something totally different. The compiler does not complain for either of these, making this very hard to debug. Overloading also has surprising ramifications. For instance, if a class overloads unary operator&, it cannot safely be forward-declared. Decision: In general, do not overload operators. The assignment operator (operator=), in particular, is insidious and should be avoided. You can define functions like Equals() and CopyFrom() if you need them. Likewise, avoid the dangerous unary operator& at all costs, if there's any possibility the class might be forward-declared. However, there may be rare cases where you need to overload an operator to interoperate with templates or "standard" C++ classes (such as operator<<(ostream&, const T&) for logging). These are acceptable if fully justified, but you should try to avoid these whenever possible. In particular, do not overload operator== or operator< just so that your class can be used as a key in an STL container; instead, you should create equality and comparison functor types when declaring the container. Some of the STL algorithms do require you to overload operator==, and you may do so in these cases, provided you document why. See also Copy Constructors and Function Overloading. Access Control link ▶Make data members private, and provide access to them through accessor functions as needed (for technical reasons, we allow data members of a test fixture class to be protected when using Google Test). Typically a variable would be called foo_ and the accessor function foo(). You may also want a mutator function set_foo(). Exception: static const data members (typically called kFoo) need not be private. The definitions of accessors are usually inlined in the header file. See also Inheritance and Function Names. Declaration Order link ▶Use the specified order of declarations within a class: public: before private:, methods before data members (variables), etc. Your class definition should start with its public: section, followed by its protected: section and then its private: section. If any of these sections are empty, omit them. Within each section, the declarations generally should be in the following order: Typedefs and Enums Constants (static const data members) Constructors Destructor Methods, including static methods Data Members (except static const data members) Friend declarations should always be in the private section, and the DISALLOW_COPY_AND_ASSIGN macro invocation should be at the end of the private: section. It should be the last thing in the class. See Copy Constructors. Method definitions in the corresponding .cc file should be the same as the declaration order, as much as possible. Do not put large method definitions inline in the class definition. Usually, only trivial or performance-critical, and very short, methods may be defined inline. See Inline Functions for more details. Write Short Functions link ▶Prefer small and focused functions. We recognize that long functions are sometimes appropriate, so no hard limit is placed on functions length. If a function exceeds about 40 lines, think about whether it can be broken up without harming the structure of the program. Even if your long function works perfectly now, someone modifying it in a few months may add new behavior. This could result in bugs that are hard to find. Keeping your functions short and simple makes it easier for other people to read and modify your code. You could find long and complicated functions when working with some code. Do not be intimidated by modifying existing code: if working with such a function proves to be difficult, you find that errors are hard to debug, or you want to use a piece of it in several different contexts, consider breaking up the function into smaller and more manageable pieces. Google-Specific Magic There are various tricks and utilities that we use to make C++ code more robust, and various ways we use C++ that may differ from what you see elsewhere. Smart Pointers link ▶If you actually need pointer semantics, scoped_ptr is great. You should only use std::tr1::shared_ptr under very specific conditions, such as when objects need to be held by STL containers. You should never use auto_ptr. "Smart" pointers are objects that act like pointers but have added semantics. When a scoped_ptr is destroyed, for instance, it deletes the object it's pointing to. shared_ptr is the same way, but implements reference-counting so only the last pointer to an object deletes it. Generally speaking, we prefer that we design code with clear object ownership. The clearest object ownership is obtained by using an object directly as a field or local variable, without using pointers at all. On the other extreme, by their very definition, reference counted pointers are owned by nobody. The problem with this design is that it is easy to create circular references or other strange conditions that cause an object to never be deleted. It is also slow to perform atomic operations every time a value is copied or assigned. Although they are not recommended, reference counted pointers are sometimes the simplest and most elegant way to solve a problem. cpplint link ▶Use cpplint.py to detect style errors. cpplint.py is a tool that reads a source file and identifies many style errors. It is not perfect, and has both false positives and false negatives, but it is still a valuable tool. False positives can be ignored by putting // NOLINT at the end of the line. Some projects have instructions on how to run cpplint.py from their project tools. If the project you are contributing to does not, you can download cpplint.py separately. Other C++ Features Reference Arguments link ▶All parameters passed by reference must be labeled const. Definition: In C, if a function needs to modify a variable, the parameter must use a pointer, eg int foo(int *pval). In C++, the function can alternatively declare a reference parameter: int foo(int &val). Pros: Defining a parameter as reference avoids ugly code like (*pval)++. Necessary for some applications like copy constructors. Makes it clear, unlike with pointers, that NULL is not a possible value. Cons: References can be confusing, as they have value syntax but pointer semantics. Decision: Within function parameter lists all references must be const: void Foo(const string &in, string *out); In fact it is a very strong convention in Google code that input arguments are values or const references while output arguments are pointers. Input parameters may be const pointers, but we never allow non-const reference parameters. One case when you might want an input parameter to be a const pointer is if you want to emphasize that the argument is not copied, so it must exist for the lifetime of the object; it is usually best to document this in comments as well. STL adapters such as bind2nd and mem_fun do not permit reference parameters, so you must declare functions with pointer parameters in these cases, too. Function Overloading link ▶Use overloaded functions (including constructors) only if a reader looking at a call site can get a good idea of what is happening without having to first figure out exactly which overload is being called. Definition: You may write a function that takes a const string& and overload it with another that takes const char*. class MyClass { public: void Analyze(const string &text); void Analyze(const char *text, size_t textlen); }; Pros: Overloading can make code more intuitive by allowing an identically-named function to take different arguments. It may be necessary for templatized code, and it can be convenient for Visitors. Cons: If a function is overloaded by the argument types alone, a reader may have to understand C++'s complex matching rules in order to tell what's going on. Also many people are confused by the semantics of inheritance if a derived class overrides only some of the variants of a function. Decision: If you want to overload a function, consider qualifying the name with some information about the arguments, e.g., AppendString(), AppendInt() rather than just Append(). Default Arguments link ▶We do not allow default function parameters, except in a few uncommon situations explained below. Pros: Often you have a function that uses lots of default values, but occasionally you want to override the defaults. Default parameters allow an easy way to do this without having to define many functions for the rare exceptions. Cons: People often figure out how to use an API by looking at existing code that uses it. Default parameters are more difficult to maintain because copy-and-paste from previous code may not reveal all the parameters. Copy-and-pasting of code segments can cause major problems when the default arguments are not appropriate for the new code. Decision: Except as described below, we require all arguments to be explicitly specified, to force programmers to consider the API and the values they are passing for each argument rather than silently accepting defaults they may not be aware of. One specific exception is when default arguments are used to simulate variable-length argument lists. // Support up to 4 params by using a default empty AlphaNum. string StrCat(const AlphaNum &a, const AlphaNum &b = gEmptyAlphaNum, const AlphaNum &c = gEmptyAlphaNum, const AlphaNum &d = gEmptyAlphaNum); Variable-Length Arrays and alloca() link ▶We do not allow variable-length arrays or alloca(). Pros: Variable-length arrays have natural-looking syntax. Both variable-length arrays and alloca() are very efficient. Cons: Variable-length arrays and alloca are not part of Standard C++. More importantly, they allocate a data-dependent amount of stack space that can trigger difficult-to-find memory overwriting bugs: "It ran fine on my machine, but dies mysteriously in production". Decision: Use a safe allocator instead, such as scoped_ptr/scoped_array. Friends link ▶We allow use of friend classes and functions, within reason. Friends should usually be defined in the same file so that the reader does not have to look in another file to find uses of the private members of a class. A common use of friend is to have a FooBuilder class be a friend of Foo so that it can construct the inner state of Foo correctly, without exposing this state to the world. In some cases it may be useful to make a unittest class a friend of the class it tests. Friends extend, but do not break, the encapsulation boundary of a class. In some cases this is better than making a member public when you want to give only one other class access to it. However, most classes should interact with other classes solely through their public members. Exceptions link ▶We do not use C++ exceptions. Pros: Exceptions allow higher levels of an application to decide how to handle "can't happen" failures in deeply nested functions, without the obscuring and error-prone bookkeeping of error codes. Exceptions are used by most other modern languages. Using them in C++ would make it more consistent with Python, Java, and the C++ that others are familiar with. Some third-party C++ libraries use exceptions, and turning them off internally makes it harder to integrate with those libraries. Exceptions are the only way for a constructor to fail. We can simulate this with a factory function or an Init() method, but these require heap allocation or a new "invalid" state, respectively. Exceptions are really handy in testing frameworks. Cons: When you add a throw statement to an existing function, you must examine all of its transitive callers. Either they must make at least the basic exception safety guarantee, or they must never catch the exception and be happy with the program terminating as a result. For instance, if f() calls g() calls h(), and h throws an exception that f catches, g has to be careful or it may not clean up properly. More generally, exceptions make the control flow of programs difficult to evaluate by looking at code: functions may return in places you don't expect. This causes maintainability and debugging difficulties. You can minimize this cost via some rules on how and where exceptions can be used, but at the cost of more that a developer needs to know and understand. Exception safety requires both RAII and different coding practices. Lots of supporting machinery is needed to make writing correct exception-safe code easy. Further, to avoid requiring readers to understand the entire call graph, exception-safe code must isolate logic that writes to persistent state into a "commit" phase. This will have both benefits and costs (perhaps where you're forced to obfuscate code to isolate the commit). Allowing exceptions would force us to always pay those costs even when they're not worth it. Turning on exceptions adds data to each binary produced, increasing compile time (probably slightly) and possibly increasing address space pressure. The availability of exceptions may encourage developers to throw them when they are not appropriate or recover from them when it's not safe to do so. For example, invalid user input should not cause exceptions to be thrown. We would need to make the style guide even longer to document these restrictions! Decision: On their face, the benefits of using exceptions outweigh the costs, especially in new projects. However, for existing code, the introduction of exceptions has implications on all dependent code. If exceptions can be propagated beyond a new project, it also becomes problematic to integrate the new project into existing exception-free code. Because most existing C++ code at Google is not prepared to deal with exceptions, it is comparatively difficult to adopt new code that generates exceptions. Given that Google's existing code is not exception-tolerant, the costs of using exceptions are somewhat greater than the costs in a new project. The conversion process would be slow and error-prone. We don't believe that the available alternatives to exceptions, such as error codes and assertions, introduce a significant burden. Our advice against using exceptions is not predicated on philosophical or moral grounds, but practical ones. Because we'd like to use our open-source projects at Google and it's difficult to do so if those projects use exceptions, we need to advise against exceptions in Google open-source projects as well. Things would probably be different if we had to do it all over again from scratch. There is an exception to this rule (no pun intended) for Windows code. Run-Time Type Information (RTTI) link ▶We do not use Run Time Type Information (RTTI). Definition: RTTI allows a programmer to query the C++ class of an object at run time. Pros: It is useful in some unittests. For example, it is useful in tests of factory classes where the test has to verify that a newly created object has the expected dynamic type. In rare circumstances, it is useful even outside of tests. Cons: A query of type during run-time typically means a design problem. If you need to know the type of an object at runtime, that is often an indication that you should reconsider the design of your class. Decision: Do not use RTTI, except in unittests. If you find yourself in need of writing code that behaves differently based on the class of an object, consider one of the alternatives to querying the type. Virtual methods are the preferred way of executing different code paths depending on a specific subclass type. This puts the work within the object itself. If the work belongs outside the object and instead in some processing code, consider a double-dispatch solution, such as the Visitor design pattern. This allows a facility outside the object itself to determine the type of class using the built-in type system. If you think you truly cannot use those ideas, you may use RTTI. But think twice about it. :-) Then think twice again. Do not hand-implement an RTTI-like workaround. The arguments against RTTI apply just as much to workarounds like class hierarchies with type tags. Casting link ▶Use C++ casts like static_cast(). Do not use other cast formats like int y = (int)x; or int y = int(x);. Definition: C++ introduced a different cast system from C that distinguishes the types of cast operations. Pros: The problem with C casts is the ambiguity of the operation; sometimes you are doing a conversion (e.g., (int)3.5) and sometimes you are doing a cast (e.g., (int)"hello"); C++ casts avoid this. Additionally C++ casts are more visible when searching for them. Cons: The syntax is nasty. Decision: Do not use C-style casts. Instead, use these C++-style casts. Use static_cast as the equivalent of a C-style cast that does value conversion, or when you need to explicitly up-cast a pointer from a class to its superclass. Use const_cast to remove the const qualifier (see const). Use reinterpret_cast to do unsafe conversions of pointer types to and from integer and other pointer types. Use this only if you know what you are doing and you understand the aliasing issues. Do not use dynamic_cast except in test code. If you need to know type information at runtime in this way outside of a unittest, you probably have a design flaw. Streams link ▶Use streams only for logging. Definition: Streams are a replacement for printf() and scanf(). Pros: With streams, you do not need to know the type of the object you are printing. You do not have problems with format strings not matching the argument list. (Though with gcc, you do not have that problem with printf either.) Streams have automatic constructors and destructors that open and close the relevant files. Cons: Streams make it difficult to do functionality like pread(). Some formatting (particularly the common format string idiom %.*s) is difficult if not impossible to do efficiently using streams without using printf-like hacks. Streams do not support operator reordering (the %1s directive), which is helpful for internationalization. Decision: Do not use streams, except where required by a logging interface. Use printf-like routines instead. There are various pros and cons to using streams, but in this case, as in many other cases, consistency trumps the debate. Do not use streams in your code. Extended Discussion There has been debate on this issue, so this explains the reasoning in greater depth. Recall the Only One Way guiding principle: we want to make sure that whenever we do a certain type of I/O, the code looks the same in all those places. Because of this, we do not want to allow users to decide between using streams or using printf plus Read/Write/etc. Instead, we should settle on one or the other. We made an exception for logging because it is a pretty specialized application, and for historical reasons. Proponents of streams have argued that streams are the obvious choice of the two, but the issue is not actually so clear. For every advantage of streams they point out, there is an equivalent disadvantage. The biggest advantage is that you do not need to know the type of the object to be printing. This is a fair point. But, there is a downside: you can easily use the wrong type, and the compiler will not warn you. It is easy to make this kind of mistake without knowing when using streams. cout << this; // Prints the address cout << *this; // Prints the contents The compiler does not generate an error because << has been overloaded. We discourage overloading for just this reason. Some say printf formatting is ugly and hard to read, but streams are often no better. Consider the following two fragments, both with the same typo. Which is easier to discover? cerr << "Error connecting to '" hostname.first << ":" hostname.second << ": " hostname.first, foo->bar()->hostname.second, strerror(errno)); And so on and so forth for any issue you might bring up. (You could argue, "Things would be better with the right wrappers," but if it is true for one scheme, is it not also true for the other? Also, remember the goal is to make the language smaller, not add yet more machinery that someone has to learn.) Either path would yield different advantages and disadvantages, and there is not a clearly superior solution. The simplicity doctrine mandates we settle on one of them though, and the majority decision was on printf + read/write. Preincrement and Predecrement link ▶Use prefix form (++i) of the increment and decrement operators with iterators and other template objects. Definition: When a variable is incremented (++i or i++) or decremented (--i or i--) and the value of the expression is not used, one must decide whether to preincrement (decrement) or postincrement (decrement). Pros: When the return value is ignored, the "pre" form (++i) is never less efficient than the "post" form (i++), and is often more efficient. This is because post-increment (or decrement) requires a copy of i to be made, which is the value of the expression. If i is an iterator or other non-scalar type, copying i could be expensive. Since the two types of increment behave the same when the value is ignored, why not just always pre-increment? Cons: The tradition developed, in C, of using post-increment when the expression value is not used, especially in for loops. Some find post-increment easier to read, since the "subject" (i) precedes the "verb" (++), just like in English. Decision: For simple scalar (non-object) values there is no reason to prefer one form and we allow either. For iterators and other template types, use pre-increment. Use of const link ▶We strongly recommend that you use const whenever it makes sense to do so. Definition: Declared variables and parameters can be preceded by the keyword const to indicate the variables are not changed (e.g., const int foo). Class functions can have the const qualifier to indicate the function does not change the state of the class member variables (e.g., class Foo { int Bar(char c) const; };). Pros: Easier for people to understand how variables are being used. Allows the compiler to do better type checking, and, conceivably, generate better code. Helps people convince themselves of program correctness because they know the functions they call are limited in how they can modify your variables. Helps people know what functions are safe to use without locks in multi-threaded programs. Cons: const is viral: if you pass a const variable to a function, that function must have const in its prototype (or the variable will need a const_cast). This can be a particular problem when calling library functions. Decision: const variables, data members, methods and arguments add a level of compile-time type checking; it is better to detect errors as soon as possible. Therefore we strongly recommend that you use const whenever it makes sense to do so: If a function does not modify an argument passed by reference or by pointer, that argument should be const. Declare methods to be const whenever possible. Accessors should almost always be const. Other methods should be const if they do not modify any data members, do not call any non-const methods, and do not return a non-const pointer or non-const reference to a data member. Consider making data members const whenever they do not need to be modified after construction. However, do not go crazy with const. Something like const int * const * const x; is likely overkill, even if it accurately describes how const x is. Focus on what's really useful to know: in this case, const int** x is probably sufficient. The mutable keyword is allowed but is unsafe when used with threads, so thread safety should be carefully considered first. Where to put the const Some people favor the form int const *foo to const int* foo. They argue that this is more readable because it's more consistent: it keeps the rule that const always follows the object it's describing. However, this consistency argument doesn't apply in this case, because the "don't go crazy" dictum eliminates most of the uses you'd have to be consistent with. Putting the const first is arguably more readable, since it follows English in putting the "adjective" (const) before the "noun" (int). That said, while we encourage putting const first, we do not require it. But be consistent with the code around you! Integer Types link ▶Of the built-in C++ integer types, the only one used is int. If a program needs a variable of a different size, use a precise-width integer type from , such as int16_t. Definition: C++ does not specify the sizes of its integer types. Typically people assume that short is 16 bits, int is 32 bits, long is 32 bits and long long is 64 bits. Pros: Uniformity of declaration. Cons: The sizes of integral types in C++ can vary based on compiler and architecture. Decision: defines types like int16_t, uint32_t, int64_t, etc. You should always use those in preference to short, unsigned long long and the like, when you need a guarantee on the size of an integer. Of the C integer types, only int should be used. When appropriate, you are welcome to use standard types like size_t and ptrdiff_t. We use int very often, for integers we know are not going to be too big, e.g., loop counters. Use plain old int for such things. You should assume that an int is at least 32 bits, but don't assume that it has more than 32 bits. If you need a 64-bit integer type, use int64_t or uint64_t. For integers we know can be "big", use int64_t. You should not use the unsigned integer types such as uint32_t, unless the quantity you are representing is really a bit pattern rather than a number, or unless you need defined twos-complement overflow. In particular, do not use unsigned types to say a number will never be negative. Instead, use assertions for this. On Unsigned Integers Some people, including some textbook authors, recommend using unsigned types to represent numbers that are never negative. This is intended as a form of self-documentation. However, in C, the advantages of such documentation are outweighed by the real bugs it can introduce. Consider: for (unsigned int i = foo.Length()-1; i >= 0; --i) ... This code will never terminate! Sometimes gcc will notice this bug and warn you, but often it will not. Equally bad bugs can occur when comparing signed and unsigned variables. Basically, C's type-promotion scheme causes unsigned types to behave differently than one might expect. So, document that a variable is non-negative using assertions. Don't use an unsigned type. 64-bit Portability link ▶Code should be 64-bit and 32-bit friendly. Bear in mind problems of printing, comparisons, and structure alignment. printf() specifiers for some types are not cleanly portable between 32-bit and 64-bit systems. C99 defines some portable format specifiers. Unfortunately, MSVC 7.1 does not understand some of these specifiers and the standard is missing a few, so we have to define our own ugly versions in some cases (in the style of the standard include file inttypes.h): // printf macros for size_t, in the style of inttypes.h #ifdef _LP64 #define __PRIS_PREFIX "z" #else #define __PRIS_PREFIX #endif // Use these macros after a % in a printf format string // to get correct 32/64 bit behavior, like this: // size_t size = records.size(); // printf("%"PRIuS"\n", size); #define PRIdS __PRIS_PREFIX "d" #define PRIxS __PRIS_PREFIX "x" #define PRIuS __PRIS_PREFIX "u" #define PRIXS __PRIS_PREFIX "X" #define PRIoS __PRIS_PREFIX "o" Type DO NOT use DO use Notes void * (or any pointer) %lx %p int64_t %qd, %lld %"PRId64" uint64_t %qu, %llu, %llx %"PRIu64", %"PRIx64" size_t %u %"PRIuS", %"PRIxS" C99 specifies %zu ptrdiff_t %d %"PRIdS" C99 specifies %zd Note that the PRI* macros expand to independent strings which are concatenated by the compiler. Hence if you are using a non-constant format string, you need to insert the value of the macro into the format, rather than the name. It is still possible, as usual, to include length specifiers, etc., after the % when using the PRI* macros. So, e.g. printf("x = %30"PRIuS"\n", x) would expand on 32-bit Linux to printf("x = %30" "u" "\n", x), which the compiler will treat as printf("x = %30u\n", x). Remember that sizeof(void *) != sizeof(int). Use intptr_t if you want a pointer-sized integer. You may need to be careful with structure alignments, particularly for structures being stored on disk. Any class/structure with a int64_t/uint64_t member will by default end up being 8-byte aligned on a 64-bit system. If you have such structures being shared on disk between 32-bit and 64-bit code, you will need to ensure that they are packed the same on both architectures. Most compilers offer a way to alter structure alignment. For gcc, you can use __attribute__((packed)). MSVC offers #pragma pack() and __declspec(align()). Use the LL or ULL suffixes a

集合了所有的 Unix命令大全登陆服务器时输入公帐号 openlab-open123 telnet 192.168.0.23 自己帐号 sd08077-you0 ftp工具 192.168.0.202 tools-toolss 老师测评网址 http://172.16.0.198:8080/poll/ 各个 shell 可互相切换 ksh:$ sh:$ csh:guangzhou% bash:bash-3.00$ 一、注意事项命令和参数之间必需用空格隔开，参数和参数之间也必需用空格隔开。一行不能超过256个字符；大小写有区分。二、特殊字符含义文件名以“.”开头的都是隐藏文件/目录，只需在文件/目录名前加“.”就可隐藏它。 ~/ 表示主目录。 ./ 当前目录(一个点)。 ../ 上一级目录(两个点)。 ; 多个命令一起用。 > >> 输出重定向。将一个命令的输出内容写入到一个文件里面。如果该文件存在，就将该文件的内容覆盖；如果不存在就先创建该文件，然后再写入内容。输出重定向，意思就是说，将原来屏幕输出变为文件输出，即将内容输到文件中。 < << 输入重定向。本来命令是通过键盘得到输入的，但是用小于号，就能够使命令从文件中得到输入。 \ 表示未写完，回车换行再继续。 * 匹配零个或者多个字符。 ? 匹配一个字符。 [] 匹配中括号里的内容[a-z][A-Z][0-9]。！事件。 $ 取环境变量的值。 | 管道。把前一命令的输出作为后一命令的输入，把几个命令连接起来。｜经常跟tee连用，tee 把内容保存到文档并显示出来。三、通用后接命令符 -a 所有(all)。 -e 所有(every)，比a更详细。 -f 取消保护。 -i 添加提示。 -p 强制执行。 -r 目录管理。分屏显示的中途操作空格继续打开下一屏；回车继续打开下一行； b 另外开上一屏； f 另外开下一屏； h 帮助； q或Ctrl+C 退出； /字符串从上往下查找匹配的字符串；？字符串从下往上查找匹配的字符串； n 继续查找。四、退出命令 exit 退出; DOS内部命令用于退出当前的命令处理器(COMMAND.COM) 恢复前一个命令处理器。 Ctrl+d 跟exit一样效果，表中止本次操作。 logout 当csh时可用来退出，其他shell不可用。 clear 清屏，清除(之前的内容并未删除，只是没看到，拉回上面可以看回)。五、目录管理命令 pwd 显示当前所在目录，打印当前目录的绝对路径。 cd 进入某目录，DOS内部命令显示或改变当前目录。 cd回车/cd ~ 都是回到自己的主目录。 cd . 当前目录(空格再加一个点)。 cd .. 回到上一级目录(空格再加两个点)。 cd ../.. 向上两级。 cd /user/s0807 从绝对路径去到某目录。 cd ~/s0807 直接进入主目录下的某目录(“cd ~"相当于主目录的路径的简写)。 ls 显示当前目录的所有目录和文件。用法 ls [-aAbcCdeEfFghHilLmnopqrRstux1@] [file...] ls /etc/ 显示某目录下的所有文件和目录，如etc目录下的。 ls -l (list)列表显示文件(默认按文件名排序)，显示文件的权限、硬链接数(即包含文件数,普通文件是1，目录1+)、用户、组名、大小、修改日期、文件名。 ls -t (time)按修改时间排序，显示目录和文件。 ls -lt 是“-l”和“-t”的组合，按时间顺序显示列表。 ls -F 显示文件类型，目录“/ ”结尾；可执行文件“*”结尾；文本文件(none)，没有结尾。 ls -R 递归显示目录结构。即该目录下的文件和各个副目录下的文件都一一显示。 ls -a 显示所有文件，包括隐藏文件。文件权限 r 读权限。对普通文件来说，是读取该文件的权限；对目录来说，是获得该目录下的文件信息。 w 写权限。对文件，是修改；对目录，是增删文件与子目录。 (注删除没有写权限的文件可以用 rm -f ，这是为了操作方便，是人性化的设计)。 x 执行权限；对目录，是进入该目录 - 表示没有权限形式 - rw- r-- r-- 其中第一个是文件类型(-表普通文件，d表目录，l表软链接文件) 第2~4个是属主，生成文件时登录的人，权限最高，用u表示第5~7个是属组，系统管理员分配的同组的一个或几个人，用g表示第8~10个是其他人，除属组外的人，用o表示所有人，包括属主、属组及其他人，用a表示 chmod 更改权限；用法 chmod [-fR] <绝对模式> 文件 ... chmod [-fR] <符号模式列表> 文件 ... 其中 <符号模式列表> 是一个用逗号分隔的表 [ugoa]{+|-|=}[rwxXlstugo] chmod u+rw 给用户加权限。同理，u-rw也可以减权限。 chmod u=rw 给用户赋权限。与加权限不一样，赋权限有覆盖的效果。主要形式有如下几种 chmod u+rw chmod u=rw chmod u+r, u+w chmod u+rw,g+w, o+r chmod 777( 用数字的方式设置权限是最常用的) 数字表示权限时，各数位分别表示属主、属组及其他人；其中，1是执行权(Execute)，2是写权限(Write)，4是读权限(Read)，具体权限相当于三种权限的数相加，如7＝1+2+4，即拥有读写和执行权。另外,临时文件/目录的权限为rwt，可写却不可删,关机后自动删除；建临时目录:chmod 777 目录名，再chmod +t 目录名。 id 显示用户有效的uid(用户字)和gid(组名) 用法 id [-ap] [user] id 显示自己的。 id root 显示root的。 id -a root 显示用户所在组的所有组名(如root用户，是所有组的组员) df 查看文件系统，查看数据区用法 df [-F FSType] [-abeghklntVvZ] [-o FSType 特定选项] [目录 | 块设备 | 资源] df -k 以kbytes显示文件大小的查看文件系统方式六、显示文件内容 more 分屏显示文件的内容。用法 more [-cdflrsuw] [-行] [+行号] [+/模式] [文件名 ...]。显示7个信息:用户名密码用户id(uid) 组id(gid) 描述信息(一般为空) 用户主目录 login shell(登录shell) cat 显示文件内容，不分屏(一般用在小文件，大文件显示不下)；合并文件，仅在屏幕上合并，并不改变原文件。用法 cat [ -usvtebn ] [-|文件] ... tail 实时监控文件，一般用在日志文件，可以只看其中的几行。用法 tail [+/-[n][lbc][f]] [文件] tail [+/-[n][l][r|f]] [文件] 七、文件/目录的增删 echo 显示一行内容。 touch 如果文件/目录不存在，则创建新文件/目录；如果文件存在，那么就是更新该文件的最后访问时间，用法 touch [-acm] [-r ref_file] 文件... touch [-acm] [MMDDhhmm[yy]] 文件... touch [-acm] [-t [[CC]YY]MMDDhhmm[.SS]] file... mkdir 创建目录(必须有创建目录的权限) 用法 mkdir [-m 模式] [-p] dirname ... mkdir dir1/dir2 在dir1下建dir2 mkdir dir13 dir4 dir5 连建多个 mkdir ~/games 用户主目录下建(默认在当前目录下创建) mkdir -p dir6/dir7/dir8 强制创建dir8；若没有前面的目录，会自动创建dir6和dir7。不用-p时，若没有dir6/dir7，则创建失败。 cp 复制文件/目录 cp 源文件目标文件复制文件；若已有文件则覆盖 cp -r 源目录目标目录复制目录；若已有目录则把源目录复制到目标目录下，没有目标目录时，相当于完全复制源目录，只是文件名不同。 cp beans apple dir2 把beans、apple文件复制到dir2目录下 cp -i beans apple 增加是否覆盖的提示 mv 移动或重命名文件/目录用法 mv [-f] [-i] f1 f2 mv [-f] [-i] f1 ... fn d1 mv [-f] [-i] d1 d2 mv 源文件名目标文件名若目标文件名还没有,则是源文件重命名为目标文件；若目标文件已存在，则源文件覆盖目标文件。 mv 源文件名目标目录移动文件 mv 源目录目标目录若目标目录不存在，则源目录重命名；若目标目录已存在，则源目录移动到目标目录下。 rm 删除文件/目录用法 rm [-fiRr] 文件 ... rm 文件名删除文件。 rm -r 目录名删除目录。 rm –f 文件只要是该文件或者目录的拥有者,无论是否有权限删除,都可以用这个命令参数强行删除。 rm -rf * 删除所有文件及目录 rmdir 删除空目录。只可以删除空目录。 ln 创建硬链接或软链接，硬链接＝同一文件的多个名字；软链接＝快捷方式用法 ln [-f] [-n] [-s] f1 [f2] ln [-f] [-n] [-s] f1 ... fn d1 ln [-f] [-n] -s d1 d2 ln file1 file1.ln 创建硬链接。感觉是同一文件，删除一个，对另一个没有影响；须两个都删除才算删除。 ln -s file1 file1.sln 创建软链接。可跨系统操作，冲破操作权限；也是快捷方式。八、时间显示 date 显示时间，精确到秒用法 date [-u] mmddHHMM[[cc]yy][.SS] date [-u] [+format] date -a [-]sss[.fff] cal 显示日历 cal 9 2008 显示2008年9月的日历； cal 显示当月的用法 cal [ [月] 年 ] 九、帮助 man 帮助( format and display the on-line manual pages) 用法 man [-] [-adFlrt] [-M 路径] [-T 宏软件包] [-s 段] 名称 ... man [-] [-adFlrt] [-M path] [-T macro-package] [-s section] name... man [-M 路径] -k 关键字 ... man [-M 路径] -f 文件 ... awk 按一定格式输出(pattern scanning and processing language) 用法 awk [-Fc] [-f 源代码 | 'cmds'] [文件] 十、vi 底行模式／？命令模式 i a o 输入模式 vi 的使用方法 1、光标 h 左 j 下 k 上 l 右 set nu 显示行号(set nonu) 21 光标停在指定行 21G 第N行 (G到文件尾，1G到文件头) 如果要将光标移动到文件第一行，那么就按 1G H 屏幕头 M 屏幕中间 L 屏幕底 ^ 或 shift+6 行首 $ 或 shift+4 行尾 Ctrl+f 下翻 Ctrl+b 上翻 2、输入 (输入模式) o 光标往下换一行 O (大写字母o)在光标所在行上插入一空行 i 在光标所在位置的前面插入字母 a 在光标所在位置的后面插入一个新字母退出插入状态。 3、修改替换 r 替换一个字符 dd 删除行，剪切行 (5dd删除5行) 5,10d 删除 5 至 10 行(包括第 5行和第 10 行) x 删除一个字符 dw 删除词，剪切词。 ( 3dw删除 3 单词) cw 替换一个单词。 (cw 和 dw 的区别 cw 删除某一个单词后直接进入编辑模式，而dw删除词后仍处于命令模式) cc 替换一行 C 替换从光标到行尾 yy 复制行 (用法同下的 Y ，见下行) Y 将光标移动到要复制行位置，按yy。当你想粘贴的时候，请将光标移动到你想复制的位置的前一个位置，然后按 p yw 复制词 p 当前行下粘贴 1,2co3 复制行1，2在行3之后 4,5m6 移动行4，5在行6之后 u 当你的前一个命令操作是一个误操作的时候，那么可以按一下 u键，即可复原。只能撤销一次 r file2 在光标所在处插入另一个文件 ~ 将字母变成大写 J 可以将当前行与下一行连接起来 /字符串从上往下找匹配的字符串 ?字符串从下往上找匹配的字符串 n 继续查找 1,$s/旧串/新串/g 替换全文(或者 %s/旧串/新串/g) (1表示从第一行开始) 没有g则只替换一次，加g替换所有 3、存盘和退出 w 存盘 w newfile 存成新文件 wq 存盘再退出VI(或者ZZ或 X) q! 强行退出不存盘查看用户 users 显示在线用户(仅显示用户名)。 who 显示在线用户，但比users更详细，包括用户名、终端号、登录时间、IP地址。 who am i 仅显示自己，(但包括用户名、端口、登录时间、IP地址；信息量＝who)。 whoami 也仅显示自己，但只有用户名(仅显示自己的有效的用户名)。 w 显示比who更多内容，还包括闲置时间、占CPU、平均占用CPU、执行命令。用法 w [ -hlsuw ] [ 用户 ] su 改变用户，需再输入密码。用法 su [-] [ username [ arg ... ] ] su －相当于退出再重新登录。查找 find 查找文件用法 find [-H | -L] 路径列表谓词列表 find / -name perl 从根目录开始查找名为perl的文件。 find . -mtime 10 -print 从当前目录查找距离现在10天时修改的文件，显示在屏幕上。 (注 “10”表示第10天的时候；如果是“+10”表示10天以外的范围；“-10”表示10天以内的范围。) grep 文件中查找字符；有过滤功能，只列出想要的内容用法 grep -hblcnsviw 模式文件 . . . 如 grep abc /etc/passwd 在passwd文件下找abc字符 wc 统计 -l 统计行数； -w统计单词数； -c 统计字符数如 grep wang /etc/passwd|wc -l 统计passwd文件含“wang”的行数 du 查看目录情况如 du -sk * 不加-s会显示子目录，-k按千字节排序用法 du [-a] [-d] [-h|-k] [-r] [-o|-s] [-H|-L] [文件...] 进程管理 ps 显示进程。用法 ps [ -aAdeflcjLPyZ ] [ -o 格式 ] [ -t 项列表 ] [ -u 用户列表 ] [ -U 用户列表 ] [ -G 组列表 ] [ -p 进程列表 ] [ -g 程序组列表 ] [ -s 标识符列表 ] [ -z 区域列表 ] ps 显示自己的进程。 ps －e 显示每个进程，包括空闲进程。 ps －f 显示详情。 ps －ef 组合－e和－f，所有进程的详情。 ps －U uidlist(用户列表) 具体查看某人的进程。 kill pkill sleep jobs 用法 jobs [-l ] fg ％n bg ％n stop ％n 挂起(仅csh能用) Ctrl+C Ctrl+Z 网络链接 ping usage ping host [timeout] usage ping -s [-l | U] [adLnRrv] [-A addr_family] [-c traffic_class] [-g gateway [-g gateway ...]] [-F flow_label] [-I interval] [-i interface] [-P tos] [-p port] [-t ttl] host [data_size] [npackets] ifconfig －a /sbin/ifconfig 查看本机的IP地址 netstat －rn rlogin ftp 帮助文件 [sd0807@localhost ~]$ help GNU bash, version 3.1.17(1)-release (i686-redhat-linux-gnu) These shell commands are defined internally. Type `help' to see this list. Type `help name' to find out more about the function `name'. Use `info bash' to find out more about the shell in general. Use `man -k' or `info' to find out more about commands not in this list. A star (*) next to a name means that the command is disabled. JOB_SPEC [&] (( expression )) . filename [arguments] [ arg... ] [[ expression ]] alias [-p] [name[=value] ... ] bg [job_spec ...] bind [-lpvsPVS] [-m keymap] [-f fi break [n] builtin [shell-builtin [arg ...]] caller [EXPR] case WORD in [PATTERN [| PATTERN]. cd [-L|-P] [dir] command [-pVv] command [arg ...] compgen [-abcdefgjksuv] [-o option complete [-abcdefgjksuv] [-pr] [-o continue [n] declare [-afFirtx] [-p] [name[=val dirs [-clpv] [+N] [-N] disown [-h] [-ar] [jobspec ...] echo [-neE] [arg ...] enable [-pnds] [-a] [-f filename] eval [arg ...] exec [-cl] [-a name] file [redirec exit [n] export [-nf] [name[=value] ...] or false fc [-e ename] [-nlr] [first] [last fg [job_spec] for NAME [in WORDS ... ;] do COMMA for (( exp1; exp2; exp3 )); do COM function NAME { COMMANDS ; } or NA getopts optstring name [arg] hash [-lr] [-p pathname] [-dt] [na help [-s] [pattern ...] history [-c] [-d offset] [n] or hi if COMMANDS; then COMMANDS; [ elif jobs [-lnprs] [jobspec ...] or job kill [-s sigspec | -n signum | -si let arg [arg ...] local name[=value] ... logout popd [+N | -N] [-n] printf [-v var] format [arguments] pushd [dir | +N | -N] [-n] pwd [-LP] read [-ers] [-u fd] [-t timeout] [ readonly [-af] [name[=value] ...] return [n] select NAME [in WORDS ... ;] do CO set [--abefhkmnptuvxBCHP] [-o option] [arg ...] shift [n] shopt [-pqsu] [-o long-option] opt source filename [arguments] suspend [-f] test [expr] time [-p] PIPELINE times trap [-lp] [arg signal_spec ...] true type [-afptP] name [name ...] typeset [-afFirtx] [-p] name[=valu ulimit [-SHacdfilmnpqstuvx] [limit umask [-p] [-S] [mode] unalias [-a] name [name ...] unset [-f] [-v] [name ...] until COMMANDS; do COMMANDS; done variables - Some variable names an wait [n] while COMMANDS; do COMMANDS; done { COMMANDS ; } 输入 man help BASH_BUILTINS(1) BASH_BUILTINS(1) NAME bash, :, ., [, alias, bg, bind, break, builtin, cd, command, compgen, complete, continue, declare, dirs, disown, echo, enable, eval, exec, exit, export, fc, fg, getopts, hash, help, history, jobs, kill, let, local, logout, popd, printf, pushd, pwd, read, readonly, return, set, shift, shopt, source, suspend, test, times, trap, type, typeset, ulimit, umask, una- lias, unset, wait - bash built-in commands, see bash(1) BASH BUILTIN COMMANDS Unless otherwise noted, each builtin command documented in this section as accepting options preceded by - accepts -- to signify the end of the options. For example, the :, true, false, and test builtins do not accept options. : [arguments] No effect; the command does nothing beyond expanding arguments and performing any specified redirections. A zero exit code is returned. . filename [arguments] source filename [arguments] Read and execute commands from filename in the current shell environment and return the exit status of the last command executed from filename. If filename does not contain a slash, file names in PATH are used to find the directory containing file- name. The file searched for in PATH need not be executable. When bash is not in posix mode, the current directory is searched if no file is found in PATH. If the sourcepath option to the shopt builtin command is turned off, the PATH is not searched. If any arguments are supplied, they become the positional parameters when filename is executed. Otherwise the positional parameters are unchanged. The return status is the status of the last command exited within the script (0 if no commands are executed), and false if filename is not found or cannot be read. alias [-p] [name[=value] ...] Alias with no arguments or with the -p option prints the list of aliases in the form alias name=value on standard output. When arguments are supplied, an alias is defined for each name whose value is given. A trailing space in value causes the next word to be checked for alias substitution when the alias is expanded. For each name in the argument list for which no value is supplied, the name and value of the alias is printed. Alias returns true unless a name is given for which no alias has been defined. bg [jobspec ...] Resume each suspended job jobspec in the background, as if it had been started with &. If jobspec is not present, the shell’s notion of the current job is used. bg jobspec returns 0 unless run when job control is disabled or, when run with job con- trol enabled, any specified jobspec was not found or was started without job control. bind [-m keymap] [-lpsvPSV] bind [-m keymap] [-q function] [-u function] [-r keyseq] bind [-m keymap] -f filename bind [-m keymap] -x keyseq:shell-command bind [-m keymap] keyseq:function-name bind readline-command Display current readline key and function bindings, bind a key sequence to a readline function or macro, or set a readline variable. Each non-option argument is a command as it would appear in .inputrc, but each binding or command must be passed as a sepa- rate argument; e.g., ’"\C-x\C-r": re-read-init-file’. Options, if supplied, have the following meanings: -m keymap Use keymap as the keymap to be affected by the subsequent bindings. Accept- able keymap names are emacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-move, vi-command, and vi-insert. vi is equivalent to vi-command; emacs is equivalent to emacs-standard. -l List the names of all readline functions. -p Display readline function names and bindings in such a way that they can be re-read. -P List current readline function names and bindings. -v Display readline variable names and values in such a way that they can be re- read. -V List current readline variable names and values. -s Display readline key sequences bound to macros and the strings they output in such a way that they can be re-read. -S Display readline key sequences bound to macros and the strings they output. -f filename Read key bindings from filename. -q function Query about which keys invoke the named function. -u function Unbind all keys bound to the named function. -r keyseq Remove any current binding for keyseq. -x keyseq:shell-command Cause shell-command to be executed whenever keyseq is entered. The return value is 0 unless an unrecognized option is given or an error occurred. break [n] Exit from within a for, while, until, or select loop. If n is specified, break n levels. n must be ≥ 1. If n is greater than the number of enclosing loops, all enclosing loops are exited. The return value is 0 unless the shell is not executing a loop when break is executed. builtin shell-builtin [arguments] Execute the specified shell builtin, passing it arguments, and return its exit sta- tus. This is useful when defining a function whose name is the same as a shell builtin, retaining the functionality of the builtin within the function. The cd builtin is commonly redefined this way. The return status is false if shell-builtin is not a shell builtin command. cd [-L|-P] [dir] Change the current directory to dir. The variable HOME is the default dir. The variable CDPATH defines the search path for the directory containing dir. Alterna- tive directory names in CDPATH are separated by a colon (:). A null directory name in CDPATH is the same as the current directory, i.e., ‘‘.’’. If dir begins with a slash (/), then CDPATH is not used. The -P option says to use the physical directory structure instead of following symbolic links (see also the -P option to the set builtin command); the -L option forces symbolic links to be followed. An argument of - is equivalent to $OLDPWD. If a non-empty directory name from CDPATH is used, or if - is the first argument, and the directory change is successful, the absolute path- name of the new working directory is written to the standard output. The return value is true if the directory was successfully changed; false otherwise. caller [expr] Returns the context of any active subroutine call (a shell function or a script exe- cuted with the . or source builtins. Without expr, caller displays the line number and source filename of the current subroutine call. If a non-negative integer is supplied as expr, caller displays the line number, subroutine name, and source file corresponding to that position in the current execution call stack. This extra information may be used, for example, to print a stack trace. The current frame is frame 0. The return value is 0 unless the shell is not executing a subroutine call or expr does not correspond to a valid position in the call stack. command [-pVv] command [arg ...] Run command with args suppressing the normal shell function lookup. Only builtin com- mands or commands found in the PATH are executed. If the -p option is given, the search for command is performed using a default value for PATH that is guaranteed to find all of the standard utilities. If either the -V or -v option is supplied, a description of command is printed. The -v option causes a single word indicating the command or file name used to invoke command to be displayed; the -V option produces a more verbose description. If the -V or -v option is supplied, the exit status is 0 if command was found, and 1 if not. If neither option is supplied and an error occurred or command cannot be found, the exit status is 127. Otherwise, the exit status of the command builtin is the exit status of command. compgen [option] [word] Generate possible completion matches for word according to the options, which may be any option accepted by the complete builtin with the exception of -p and -r, and write the matches to the standard output. When using the -F or -C options, the vari- ous shell variables set by the programmable completion facilities, while available, will not have useful values. The matches will be generated in the same way as if the programmable completion code had generated them directly from a completion specification with the same flags. If word is specified, only those completions matching word will be displayed. The return value is true unless an invalid option is supplied, or no matches were generated. complete [-abcdefgjksuv] [-o comp-option] [-A action] [-G globpat] [-W wordlist] [-P prefix] [-S suffix] [-X filterpat] [-F function] [-C command] name [name ...] complete -pr [name ...] Specify how arguments to each name should be completed. If the -p option is sup- plied, or if no options are supplied, existing completion specifications are printed in a way that allows them to be reused as input. The -r option removes a completion specification for each name, or, if no names are supplied, all completion specifica- tions. The process of applying these completion specifications when word completion is attempted is described above under Programmable Completion. Other options, if specified, have the following meanings. The arguments to the -G, -W, and -X options (and, if necessary, the -P and -S options) should be quoted to protect them from expansion before the complete builtin is invoked. -o comp-option The comp-option controls several aspects of the compspec’s behavior beyond the simple generation of completions. comp-option may be one of: bashdefault Perform the rest of the default bash completions if the compspec gen- erates no matches. default Use readline’s default filename completion if the compspec generates no matches. dirnames Perform directory name completion if the compspec generates no matches. filenames Tell readline that the compspec generates filenames, so it can per- form any filename-specific processing (like adding a slash to direc- tory names or suppressing trailing spaces). Intended to be used with shell functions. nospace Tell readline not to append a space (the default) to words completed at the end of the line. plusdirs After any matches defined by the compspec are generated, directory name completion is attempted and any matches are added to the results of the other actions. -A action The action may be one of the following to generate a list of possible comple- tions: alias Alias names. May also be specified as -a. arrayvar Array variable names. binding Readline key binding names. builtin Names of shell builtin commands. May also be specified as -b. command Command names. May also be specified as -c. directory Directory names. May also be specified as -d. disabled Names of disabled shell builtins. enabled Names of enabled shell builtins. export Names of exported shell variables. May also be specified as -e. file File names. May also be specified as -f. function Names of shell functions. group Group names. May also be specified as -g. helptopic Help topics as accepted by the help builtin. hostname Hostnames, as taken from the file specified by the HOSTFILE shell variable. job Job names, if job control is active. May also be specified as -j. keyword Shell reserved words. May also be specified as -k. running Names of running jobs, if job control is active. service Service names. May also be specified as -s. setopt Valid arguments for the -o option to the set builtin. shopt Shell option names as accepted by the shopt builtin. signal Signal names. stopped Names of stopped jobs, if job control is active. user User names. May also be specified as -u. variable Names of all shell variables. May also be specified as -v. -G globpat The filename expansion pattern globpat is expanded to generate the possible completions. -W wordlist The wordlist is split using the characters in the IFS special variable as delimiters, and each resultant word is expanded. The possible completions are the members of the resultant list which match the word being completed. -C command command is executed in a subshell environment, and its output is used as the possible completions. -F function The shell function function is executed in the current shell environment. When it finishes, the possible completions are retrieved from the value of the COMPREPLY array variable. -X filterpat filterpat is a pattern as used for filename expansion. It is applied to the list of possible completions generated by the preceding options and argu- ments, and each completion matching filterpat is removed from the list. A leading ! in filterpat negates the pattern; in this case, any completion not matching filterpat is removed. -P prefix prefix is added at the beginning of each possible completion after all other options have been applied. -S suffix suffix is appended to each possible completion after all other options have been applied. The return value is true unless an invalid option is supplied, an option other than -p or -r is supplied without a name argument, an attempt is made to remove a comple- tion specification for a name for which no specification exists, or an error occurs adding a completion specification. continue [n] Resume the next iteration of the enclosing for, while, until, or select loop. If n is specified, resume at the nth enclosing loop. n must be ≥ 1. If n is greater than the number of enclosing loops, the last enclosing loop (the ‘‘top-level’’ loop) is resumed. The return value is 0 unless the shell is not executing a loop when con- tinue is executed. declare [-afFirtx] [-p] [name[=value] ...] typeset [-afFirtx] [-p] [name[=value] ...] Declare variables and/or give them attributes. If no names are given then display the values of variables. The -p option will display the attributes and values of each name. When -p is used, additional options are ignored. The -F option inhibits the display of function definitions; only the function name and attributes are printed. If the extdebug shell option is enabled using shopt, the source file name and line number where the function is defined are displayed as well. The -F option implies -f. The following options can be used to restrict output to variables with the specified attribute or to give variables attributes: -a Each name is an array variable (see Arrays above). -f Use function names only. -i The variable is treated as an integer; arithmetic evaluation (see ARITHMETIC EVALUATION ) is performed when the variable is assigned a value. -r Make names readonly. These names cannot then be assigned values by subsequent assignment statements or unset. -t Give each name the trace attribute. Traced functions inherit the DEBUG and RETURN traps from the calling shell. The trace attribute has no special mean- ing for variables. -x Mark names for export to subsequent commands via the environment. Using ‘+’ instead of ‘-’ turns off the attribute instead, with the exception that +a may not be used to destroy an array variable. When used in a function, makes each name local, as with the local command. If a variable name is followed by =value, the value of the variable is set to value. The return value is 0 unless an invalid option is encountered, an attempt is made to define a function using ‘‘-f foo=bar’’, an attempt is made to assign a value to a readonly variable, an attempt is made to assign a value to an array variable without using the compound assignment syntax (see Arrays above), one of the names is not a valid shell variable name, an attempt is made to turn off readonly status for a readonly variable, an attempt is made to turn off array status for an array variable, or an attempt is made to display a non-exis- tent function with -f. dirs [-clpv] [+n] [-n] Without options, displays the list of currently remembered directories. The default display is on a single line with directory names separated by spaces. Directories are added to the list with the pushd command; the popd command removes entries from the list. +n Displays the nth entry counting from the left of the list shown by dirs when invoked without options, starting with zero. -n Displays the nth entry counting from the right of the list shown by dirs when invoked without options, starting with zero. -c Clears the directory stack by deleting all of the entries. -l Produces a longer listing; the default listing format uses a tilde to denote the home directory. -p Print the directory stack with one entry per line. -v Print the directory stack with one entry per line, prefixing each entry with its index in the stack. The return value is 0 unless an invalid option is supplied or n indexes beyond the end of the directory stack. disown [-ar] [-h] [jobspec ...] Without options, each jobspec is removed from the table of active jobs. If the -h option is given, each jobspec is not removed from the table, but is marked so that SIGHUP is not sent to the job if the shell receives a SIGHUP. If no jobspec is present, and neither the -a nor the -r option is supplied, the current job is used. If no jobspec is supplied, the -a option means to remove or mark all jobs; the -r option without a jobspec argument restricts operation to running jobs. The return value is 0 unless a jobspec does not specify a valid job. echo [-neE] [arg ...] Output the args, separated by spaces, followed by a newline. The return status is always 0. If -n is specified, the trailing newline is suppressed. If the -e option is given, interpretation of the following backslash-escaped characters is enabled. The -E option disables the interpretation of these escape characters, even on systems where they are interpreted by default. The xpg_echo shell option may be used to dynamically determine whether or not echo expands these escape characters by default. echo does not interpret -- to mean the end of options. echo interprets the following escape sequences: \a alert (bell) \b backspace \c suppress trailing newline \e an escape character \f form feed \n new line \r carriage return \t horizontal tab \v vertical tab \\ backslash \0nnn the eight-bit character whose value is the octal value nnn (zero to three octal digits) \nnn the eight-bit character whose value is the octal value nnn (one to three octal digits) \xHH the eight-bit character whose value is the hexadecimal value HH (one or two hex digits) enable [-adnps] [-f filename] [name ...] Enable and disable builtin shell commands. Disabling a builtin allows a disk command which has the same name as a shell builtin to be executed without specifying a full pathname, even though the shell normally searches for builtins before disk commands. If -n is used, each name is disabled; otherwise, names are enabled. For example, to use the test binary found via the PATH instead of the shell builtin version, run ‘‘enable -n test’’. The -f option means to load the new builtin command name from shared object filename, on systems that support dynamic loading. The -d option will delete a builtin previously loaded with -f. If no name arguments are given, or if the -p option is supplied, a list of shell builtins is printed. With no other option arguments, the list consists of all enabled shell builtins. If -n is supplied, only disabled builtins are printed. If -a is supplied, the list printed includes all builtins, with an indication of whether or not each is enabled. If -s is supplied, the output is restricted to the POSIX special builtins. The return value is 0 unless a name is not a shell builtin or there is an error loading a new builtin from a shared object. eval [arg ...] The args are read and concatenated together into a single command. This command is then read and executed by the shell, and its exit status is returned as the value of eval. If there are no args, or only null arguments, eval returns 0. exec [-cl] [-a name] [command [arguments]] If command is specified, it replaces the shell. No new process is created. The arguments become the arguments to command. If the -l option is supplied, the shell places a dash at the beginning of the zeroth arg passed to command. This is what login(1) does. The -c option causes command to be executed with an empty environ- ment. If -a is supplied, the shell passes name as the zeroth argument to the exe- cuted command. If command cannot be executed for some reason, a non-interactive shell exits, unless the shell option execfail is enabled, in which case it returns failure. An interactive shell returns failure if the file cannot be executed. If command is not specified, any redirections take effect in the current shell, and the return status is 0. If there is a redirection error, the return status is 1. exit [n] Cause the shell to exit with a status of n. If n is omitted, the exit status is that of the last command executed. A trap on EXIT is executed before the shell termi- nates. export [-fn] [name[=word]] ... export -p The supplied names are marked for automatic export to the environment of subsequently executed commands. If the -f option is given, the names refer to functions. If no names are given, or if the -p option is supplied, a list of all names that are exported in this shell is printed. The -n option causes the export property to be removed from each name. If a variable name is followed by =word, the value of the variable is set to word. export returns an exit status of 0 unless an invalid option is encountered, one of the names is not a valid shell variable name, or -f is sup- plied with a name that is not a function. fc [-e ename] [-nlr] [first] [last] fc -s [pat=rep] [cmd] Fix Command. In the first form, a range of commands from first to last is selected from the history list. First and last may be specified as a string (to locate the last command beginning with that string) or as a number (an index into the history list, where a negative number is used as an offset from the current command number). If last is not specified it is set to the current command for listing (so that ‘‘fc -l -10’’ prints the last 10 commands) and to first otherwise. If first is not speci- fied it is set to the previous command for editing and -16 for listing. The -n option suppresses the command numbers when listing. The -r option reverses the order of the commands. If the -l option is given, the commands are listed on standard output. Otherwise, the editor given by ename is invoked on a file contain- ing those commands. If ename is not given, the value of the FCEDIT variable is used, and the value of EDITOR if FCEDIT is not set. If neither variable is set, is used. When editing is complete, the edited commands are echoed and executed. In the second form, command is re-executed after each instance of pat is replaced by rep. A useful alias to use with this is ‘‘r="fc -s"’’, so that typing ‘‘r cc’’ runs the last command beginning with ‘‘cc’’ and typing ‘‘r’’ re-executes the last command. If the first form is used, the return value is 0 unless an invalid option is encoun- tered or first or last specify history lines out of range. If the -e option is sup- plied, the return value is the value of the last command executed or failure if an error occurs with the temporary file of commands. If the second form is used, the return status is that of the command re-executed, unless cmd does not specify a valid history line, in which case fc returns failure. fg [jobspec] Resume jobspec in the foreground, and make it the current job. If jobspec is not present, the shell’s notion of the current job is used. The return value is that of the command placed into the foreground, or failure if run when job control is dis- abled or, when run with job control enabled, if jobspec does not specify a valid job or jobspec specifies a job that was started without job control. getopts optstring name [args] getopts is used by shell procedures to parse positional parameters. optstring con- tains the option characters to be recognized; if a character is followed by a colon, the option is expected to have an argument, which should be separated from it by white space. The colon and question mark characters may not be used as option char- acters. Each time it is invoked, getopts places the next option in the shell vari- able name, initializing name if it does not exist, and the index of the next argument to be processed into the variable OPTIND. OPTIND is initialized to 1 each time the shell or a shell script is invoked. When an option requires an argument, getopts places that argument into the variable OPTARG. The shell does not reset OPTIND auto- matically; it must be manually reset between multiple calls to getopts within the same shell invocation if a new set of parameters is to be used. When the end of options is encountered, getopts exits with a return value greater than zero. OPTIND is set to the index of the first non-option argument, and name is set to ?. getopts normally parses the positional parameters, but if more arguments are given in args, getopts parses those instead. getopts can report errors in two ways. If the first character of optstring is a colon, silent error reporting is used. In normal operation diagnostic messages are printed when invalid options or missing option arguments are encountered. If the variable OPTERR is set to 0, no error messages will be displayed, even if the first character of optstring is not a colon. If an invalid option is seen, getopts places ? into name and, if not silent, prints an error message and unsets OPTARG. If getopts is silent, the option character found is placed in OPTARG and no diagnostic message is printed. If a required argument is not found, and getopts is not silent, a question mark (?) is placed in name, OPTARG is unset, and a diagnostic message is printed. If getopts is silent, then a colon (:) is placed in name and OPTARG is set to the option charac- ter found. getopts returns true if an option, specified or unspecified, is found. It returns false if the end of options is encountered or an error occurs. hash [-lr] [-p filename] [-dt] [name] For each name, the full file name of the command is determined by searching the directories in $PATH and remembered. If the -p option is supplied, no path search is performed, and filename is used as the full file name of the command. The -r option causes the shell to forget all remembered locations. The -d option causes the shell to forget the remembered location of each name. If the -t option is supplied, the full pathname to which each name corresponds is printed. If multiple name arguments are supplied with -t, the name is printed before the hashed full pathname. The -l option causes output to be displayed in a format that may be reused as input. If no arguments are given, or if only -l is supplied, information about remembered commands is printed. The return status is true unless a name is not found or an invalid option is supplied. help [-s] [pattern] Display helpful information about builtin commands. If pattern is specified, help gives detailed help on all commands matching pattern; otherwise help for all the builtins and shell control structures is printed. The -s option restricts the infor- mation displayed to a short usage synopsis. The return status is 0 unless no command matches pattern. history [n] history -c history -d offset history -anrw [filename] history -p arg [arg ...] history -s arg [arg ...] With no options, display the command history list with line numbers. Lines listed with a * have been modified. An argument of n lists only the last n lines. If the shell variable HISTTIMEFORMAT is set and not null, it is used as a format string for strftime(3) to display the time stamp associated with each displayed history entry. No intervening blank is printed between the formatted time stamp and the history line. If filename is supplied, it is used as the name of the history file; if not, the value of HISTFILE is used. Options, if supplied, have the following meanings: -c Clear the history list by deleting all the entries. -d offset Delete the history entry at position offset. -a Append the ‘‘new’’ history lines (history lines entered since the beginning of the current bash session) to the history file. -n Read the history lines not already read from the history file into the current history list. These are lines appended to the history file since the begin- ning of the current bash session. -r Read the contents of the history file and use them as the current history. -w Write the current history to the history file, overwriting the history file’s contents. -p Perform history substitution on the following args and display the result on the standard output. Does not store the results in the history list. Each arg must be quoted to disable normal history expansion. -s Store the args in the history list as a single entry. The last command in the history list is removed before the args are added. If the HISTTIMEFORMAT is set, the time stamp information associated with each history entry is written to the history file. The return value is 0 unless an invalid option is encountered, an error occurs while reading or writing the history file, an invalid offset is supplied as an argument to -d, or the history expansion supplied as an argument to -p fails. jobs [-lnprs] [ jobspec ... ] jobs -x command [ args ... ] The first form lists the active jobs. The options have the following meanings: -l List process IDs in addition to the normal information. -p List only the process ID of the job’s process group leader. -n Display information only about jobs that have changed status since the user was last notified of their status. -r Restrict output to running jobs. -s Restrict output to stopped jobs. If jobspec is given, output is restricted to information about that job. The return status is 0 unless an invalid option is encountered or an invalid jobspec is sup- plied. If the -x option is supplied, jobs replaces any jobspec found in command or args with the corresponding process group ID, and executes command passing it args, returning its exit status. kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ... kill -l [sigspec | exit_status] Send the signal named by sigspec or signum to the processes named by pid or jobspec. sigspec is either a case-insensitive signal name such as SIGKILL (with or without the SIG prefix) or a signal number; signum is a signal number. If sigspec is not present, then SIGTERM is assumed. An argument of -l lists the signal names. If any arguments are supplied when -l is given, the names of the signals corresponding to the arguments are listed, and the return status is 0. The exit_status argument to -l is a number specifying either a signal number or the exit status of a process termi- nated by a signal. kill returns true if at least one signal was successfully sent, or false if an error occurs or an invalid option is encountered. let arg [arg ...] Each arg is an arithmetic expression to be evaluated (see ARITHMETIC EVALUATION). If the last arg evaluates to 0, let returns 1; 0 is returned otherwise. local [option] [name[=value] ...] For each argument, a local variable named name is created, and assigned value. The option can be any of the options accepted by declare. When local is used within a function, it causes the variable name to have a visible scope restricted to that function and its children. With no operands, local writes a list of local variables to the standard output. It is an error to use local when not within a function. The return status is 0 unless local is used outside a function, an invalid name is sup- plied, or name is a readonly variable. logout Exit a login shell. popd [-n] [+n] [-n] Removes entries from the directory stack. With no arguments, removes the top direc- tory from the stack, and performs a cd to the new top directory. Arguments, if sup- plied, have the following meanings: +n Removes the nth entry counting from the left of the list shown by dirs, start- ing with zero. For example: ‘‘popd +0’’ removes the first directory, ‘‘popd +1’’ the second. -n Removes the nth entry counting from the right of the list shown by dirs, starting with zero. For example: ‘‘popd -0’’ removes the last directory, ‘‘popd -1’’ the next to last. -n Suppresses the normal change of directory when removing directories from the stack, so that only the stack is manipulated. If the popd command is successful, a dirs is performed as well, and the return status is 0. popd returns false if an invalid option is encountered, the directory stack is empty, a non-existent directory stack entry is specified, or the directory change fails. printf [-v var] format [arguments] Write the formatted arguments to the standard output under the control of the format. The format is a character string which contains three types of objects: plain charac- ters, which are simply copied to standard output, character escape sequences, which are converted and copied to the standard output, and format specifications, each of which causes printing of the next successive argument. In addition to the standard printf(1) formats, %b causes printf to expand backslash escape sequences in the cor- responding argument (except that \c terminates output, backslashes in \', \", and \? are not removed, and octal escapes beginning with \0 may contain up to four digits), and %q causes printf to output the corresponding argument in a format that can be reused as shell input. The -v option causes the output to be assigned to the variable var rather than being printed to the standard output. The format is reused as necessary to consume all of the arguments. If the format requires more arguments than are supplied, the extra format specifications behave as if a zero value or null string, as appropriate, had been supplied. The return value is zero on success, non-zero on failure. pushd [-n] [dir] pushd [-n] [+n] [-n] Adds a directory to the top of the directory stack, or rotates the stack, making the new top of the stack the current working directory. With no arguments, exchanges the top two directories and returns 0, unless the directory stack is empty. Arguments, if supplied, have the following meanings: +n Rotates the stack so that the nth directory (counting from the left of the list shown by dirs, starting with zero) is at the top. -n Rotates the stack so that the nth directory (counting from the right of the list shown by dirs, starting with zero) is at the top. -n Suppresses the normal change of directory when adding directories to the stack, so that only the stack is manipulated. dir Adds dir to the directory stack at the top, making it the new current working directory. If the pushd command is successful, a dirs is performed as well. If the first form is used, pushd returns 0 unless the cd to dir fails. With the second form, pushd returns 0 unless the directory stack is empty, a non-existent directory stack element is specified, or the directory change to the specified new current directory fails. pwd [-LP] Print the absolute pathname of the current working directory. The pathname printed contains no symbolic links if the -P option is supplied or the -o physical option to the set builtin command is enabled. If the -L option is used, the pathname printed may contain symbolic links. The return status is 0 unless an error occurs while reading the name of the current directory or an invalid option is supplied. read [-ers] [-u fd] [-t timeout] [-a aname] [-p prompt] [-n nchars] [-d delim] [name ...] One line is read from the standard input, or from the file descriptor fd supplied as an argument to the -u option, and the first word is assigned to the first name, the second word to the second name, and so on, with leftover words and their intervening separators assigned to the last name. If there are fewer words read from the input stream than names, the remaining names are assigned empty values. The characters in IFS are used to split the line into words. The backslash character (\) may be used to remove any special meaning for the next character read and for line continuation. Options, if supplied, have the following meanings: -a aname The words are assigned to sequential indices of the array variable aname, starting at 0. aname is unset before any new values are assigned. Other name arguments are ignored. -d delim The first character of delim is used to terminate the input line, rather than newline. -e If the standard input is coming from a terminal, readline (see READLINE above) is used to obtain the line. -n nchars read returns after reading nchars characters rather than waiting for a com- plete line of input. -p prompt Display prompt on standard error, without a trailing newline, before attempt- ing to read any input. The prompt is displayed only if input is coming from a terminal. -r Backslash does not act as an escape character. The backslash is considered to be part of the line. In particular, a backslash-newline pair may not be used as a line continuation. -s Silent mode. If input is coming from a terminal, characters are not echoed. -t timeout Cause read to time out and return failure if a complete line of input is not read within timeout seconds. This option has no effect if read is not reading input from the terminal or a pipe. -u fd Read input from file descriptor fd. If no names are supplied, the line read is assigned to the variable REPLY. The return code is zero, unless end-of-file is encountered, read times out, or an invalid file descriptor is supplied as the argument to -u. readonly [-apf] [name[=word] ...] The given names are marked readonly; the values of these names may not be changed by subsequent assignment. If the -f option is supplied, the functions corresponding to the names are so marked. The -a option restricts the variables to arrays. If no name arguments are given, or if the -p option is supplied, a list of all readonly names is printed. The -p option causes output to be displayed in a format that may be reused as input. If a variable name is followed by =word, the value of the vari- able is set to word. The return status is 0 unless an invalid option is encountered, one of the names is not a valid shell variable name, or -f is supplied with a name that is not a function. return [n] Causes a function to exit with the return value specified by n. If n is omitted, the return status is that of the last command executed in the function body. If used outside a function, but during execution of a script by the . (source) command, it causes the shell to stop executing that script and return either n or the exit status of the last command executed within the script as the exit status of the script. If used outside a function and not during execution of a script by ., the return status is false. Any command associated with the RETURN trap is executed before execution resumes after the function or script. set [--abefhkmnptuvxBCHP] [-o option] [arg ...] Without options, the name and value of each shell variable are displayed in a format that can be reused as input for setting or resetting the currently-set variables. Read-only variables cannot be reset. In posix mode, only shell variables are listed. The output is sorted according to the current locale. When options are specified, they set or unset shell attributes. Any arguments remaining after the options are processed are treated as values for the positional parameters and are assigned, in order, to $1, $2, ... $n. Options, if specified, have the following meanings: -a Automatically mark variables and functions which are modified or created for export to the environment of subsequent commands. -b Report the status of terminated background jobs immediately, rather than before the next primary prompt. This is effective only when job control is enabled. -e Exit immediately if a simple command (see SHELL GRAMMAR above) exits with a non-zero status. The shell does not exit if the command that fails is part of the command list immediately following a while or until keyword, part of the test in an if statement, part of a && or ││ list, or if the command’s return value is being inverted via !. A trap on ERR, if set, is executed before the shell exits. -f Disable pathname expansion. -h Remember the location of commands as they are looked up for execution. This is enabled by default. -k All arguments in the form of assignment statements are placed in the environ- ment for a command, not just those that precede the command name. -m Monitor mode. Job control is enabled. This option is on by default for interactive shells on systems that support it (see JOB CONTROL above). Back- ground processes run in a separate process group and a line containing their exit status is printed upon their completion. -n Read commands but do not execute them. This may be used to check a shell script for syntax errors. This is ignored by interactive shells. -o option-name The option-name can be one of the following: allexport Same as -a. braceexpand Same as -B. emacs Use an emacs-style command line editing interface. This is enabled by default when the shell is interactive, unless the shell is started with the --noediting option. errtrace Same as -E. functrace Same as -T. errexit Same as -e. hashall Same as -h. histexpand Same as -H. history Enable command history, as described above under HISTORY. This option is on by default in interactive shells. ignoreeof The effect is as if the shell command ‘‘IGNOREEOF=10’’ had been exe- cuted (see Shell Variables above). keyword Same as -k. monitor Same as -m. noclobber Same as -C. noexec Same as -n. noglob Same as -f. nolog Currently ignored. notify Same as -b. nounset Same as -u. onecmd Same as -t. physical Same as -P. pipefail If set, the return value of a pipeline is the value of the last (rightmost) command to exit with a non-zero status, or zero if all command

Contents Overview 1 Lesson 1: Index Concepts 3 Lesson 2: Concepts – Statistics 29 Lesson 3: Concepts – Query Optimization 37 Lesson 4: Information Collection and Analysis 61 Lesson 5: Formulating and Implementing Resolution 75 Module 6: Troubleshooting Query Performance Overview At the end of this module, you will be able to:  Describe the different types of indexes and how indexes can be used to improve performance.  Describe what statistics are used for and how they can help in optimizing query performance.  Describe how queries are optimized.  Analyze the information collected from various tools.  Formulate resolution to query performance problems. Lesson 1: Index Concepts Indexes are the most useful tool for improving query performance. Without a useful index, Microsoft® SQL Server™ must search every row on every page in table to find the rows to return. With a multitable query, SQL Server must sometimes search a table multiple times so each page is scanned much more than once. Having useful indexes speeds up finding individual rows in a table, as well as finding the matching rows needed to join two tables. What You Will Learn After completing this lesson, you will be able to:  Understand the structure of SQL Server indexes.  Describe how SQL Server uses indexes to find rows.  Describe how fillfactor can impact the performance of data retrieval and insertion.  Describe the different types of fragmentation that can occur within an index. Recommended Reading  Chapter 8: “Indexes”, Inside SQL Server 2000 by Kalen Delaney  Chapter 11: “Batches, Stored Procedures and Functions”, Inside SQL Server 2000 by Kalen Delaney Finding Rows without Indexes With No Indexes, A Table Must Be Scanned SQL Server keeps track of which pages belong to a table or index by using IAM pages. If there is no clustered index, there is a sysindexes row for the table with an indid value of 0, and that row will keep track of the address of the first IAM for the table. The IAM is a giant bitmap, and every 1 bit indicates that the corresponding extent belongs to the table. The IAM allows SQL Server to do efficient prefetching of the table’s extents, but every row still must be examined. General Index Structure All SQL Server Indexes Are Organized As B-Trees Indexes in SQL Server store their information using standard B-trees. A B-tree provides fast access to data by searching on a key value of the index. B-trees cluster records with similar keys. The B stands for balanced, and balancing the tree is a core feature of a B-tree’s usefulness. The trees are managed, and branches are grafted as necessary, so that navigating down the tree to find a value and locate a specific record takes only a few page accesses. Because the trees are balanced, finding any record requires about the same amount of resources, and retrieval speed is consistent because the index has the same depth throughout. Clustered and Nonclustered Indexes Both Index Types Have Many Common Features An index consists of a tree with a root from which the navigation begins, possible intermediate index levels, and bottom-level leaf pages. You use the index to find the correct leaf page. The number of levels in an index will vary depending on the number of rows in the table and the size of the key column or columns for the index. If you create an index using a large key, fewer entries will fit on a page, so more pages (and possibly more levels) will be needed for the index. On a qualified select, update, or delete, the correct leaf page will be the lowest page of the tree in which one or more rows with the specified key or keys reside. A qualified operation is one that affects only specific rows that satisfy the conditions of a WHERE clause, as opposed to accessing the whole table. An index can have multiple node levels An index page above the leaf is called a node page. Each index row in node pages contains an index key (or set of keys for a composite index) and a pointer to a page at the next level for which the first key value is the same as the key value in the current index row. Leaf Level contains all key values In any index, whether clustered or nonclustered, the leaf level contains every key value, in key sequence. In SQL Server 2000, the sequence can be either ascending or descending. The sysindexes table contains all sizing, location and distribution information Any information about size of indexes or tables is stored in sysindexes. The only source of any storage location information is the sysindexes table, which keeps track of the address of the root page for every index, and the first IAM page for the index or table. There is also a column for the first page of the table, but this is not guaranteed to be reliable. SQL Server can find all pages belonging to an index or table by examining the IAM pages. Sysindexes contains a pointer to the first IAM page, and each IAM page contains a pointer to the next one. The Difference between Clustered and Nonclustered Indexes The main difference between the two types of indexes is how much information is stored at the leaf. The leaf levels of both types of indexes contain all the key values in order, but they also contain other information. Clustered Indexes The Leaf Level of a Clustered Index Is the Data The leaf level of a clustered index contains the data pages, not just the index keys. Another way to say this is that the data itself is part of the clustered index. A clustered index keeps the data in a table ordered around the key. The data pages in the table are kept in a doubly linked list called the page chain. The order of pages in the page chain, and the order of rows on the data pages, is the order of the index key or keys. Deciding which key to cluster on is an important performance consideration. When the index is traversed to the leaf level, the data itself has been retrieved, not simply pointed to. Uniqueness Is Maintained In Key Values In SQL Server 2000, all clustered indexes are unique. If you build a clustered index without specifying the unique keyword, SQL Server forces uniqueness by adding a uniqueifier to the rows when necessary. This uniqueifier is a 4-byte value added as an additional sort key to only the rows that have duplicates of their primary sort key. You can see this extra value if you use DBCC PAGE to look at the actual index rows the section on indexes internal. . Finding Rows in a Clustered Index The Leaf Level of a Clustered Index Contains the Data A clustered index is like a telephone directory in which all of the rows for customers with the same last name are clustered together in the same part of the book. Just as the organization of a telephone directory makes it easy for a person to search, SQL Server quickly searches a table with a clustered index. Because a clustered index determines the sequence in which rows are stored in a table, there can only be one clustered index for a table at a time. Performance Considerations Keeping your clustered key value small increases the number of index rows that can be placed on an index page and decreases the number of levels that must be traversed. This minimizes I/O. As we’ll see, the clustered key is duplicated in every nonclustered index row, so keeping your clustered key small will allow you to have more index fit per page in all your indexes. Note The query corresponding to the slide is: SELECT lastname, firstname FROM member WHERE lastname = ‘Ota’ Nonclustered Indexes The Leaf Level of a Nonclustered Index Contains a Bookmark A nonclustered index is like the index of a textbook. The data is stored in one place and the index is stored in another. Pointers indicate the storage location of the indexed items in the underlying table. In a nonclustered index, the leaf level contains each index key, plus a bookmark that tells SQL Server where to find the data row corresponding to the key in the index. A bookmark can take one of two forms:  If the table has a clustered index, the bookmark is the clustered index key for the corresponding data row. This clustered key can be multiple column if the clustered index is composite, or is defined to be non-unique.  If the table is a heap (in other words, it has no clustered index), the bookmark is a RID, which is an actual row locator in the form File#:Page#:Slot#. Finding Rows with a NC Index on a Heap Nonclustered Indexes Are Very Efficient When Searching For A Single Row After the nonclustered key at the leaf level of the index is found, only one more page access is needed to find the data row. Searching for a single row using a nonclustered index is almost as efficient as searching for a single row in a clustered index. However, if we are searching for multiple rows, such as duplicate values, or keys in a range, anything more than a small number of rows will make the nonclustered index search very inefficient. Note The query corresponding to the slide is: SELECT lastname, firstname FROM member WHERE lastname BETWEEN ‘Master’ AND ‘Rudd’ Finding Rows with a NC Index on a Clustered Table A Clustered Key Is Used as the Bookmark for All Nonclustered Indexes If the table has a clustered index, all columns of the clustered key will be duplicated in the nonclustered index leaf rows, unless there is overlap between the clustered and nonclustered key. For example, if the clustered index is on (lastname, firstname) and a nonclustered index is on firstname, the firstname value will not be duplicated in the nonclustered index leaf rows. Note The query corresponding to the slide is: SELECT lastname, firstname, phone FROM member WHERE firstname = ‘Mike’ Covering Indexes A Covering Index Provides the Fastest Data Access A covering index contains ALL the fields accessed in the query. Normally, only the columns in the WHERE clause are helpful in determining useful indexes, but for a covering index, all columns must be included. If all columns needed for the query are in the index, SQL Server never needs to access the data pages. If even one column in the query is not part of the index, the data rows must be accessed. The leaf level of an index is the only level that contains every key value, or set of key values. For a clustered index, the leaf level is the data itself, so in reality, a clustered index ALWAYS covers any query. Nevertheless, for most of our optimization discussions, we only consider nonclustered indexes. Scanning the leaf level of a nonclustered index is almost always faster than scanning a clustered index, so covering indexes are particular valuable when we need ALL the key values of a particular nonclustered index. Example: Select an aggregate value of a column with a clustered index. Suppose we have a nonclustered index on price, this query is covered: SELECT avg(price) from titles Since the clustered key is included in every nonclustered index row, the clustered key can be included in the covering. Suppose you have a nonclustered index on price and a clustered index on title_id; then this query is covered: SELECT title_id, price FROM titles WHERE price between 10 and 20 Performance Considerations In general, you do want to keep your indexes narrow. However, if you have a critical query that just is not giving you satisfactory performance no matter what you do, you should consider creating an index to cover it, or adding one or two extra columns to an existing index, so that the query will be covered. The leaf level of a nonclustered index is like a ‘mini’ clustered index, so you can have most of the benefits of clustering, even if there already is another clustered index on the table. The tradeoff to adding more, wider indexes for covering queries are the added disk space, and more overhead for updating those columns that are now part of the index. Bug In general, SQL Server will detect when a query is covered, and detect the possible covering indexes. However, in some cases, you must force SQL Server to use a covering index by including a WHERE clause, even if the WHERE clause will return ALL the rows in the table. This is SHILOH bug #352079 Steps to reproduce 1. Make copy of orders table from Northwind: USE Northwind CREATE TABLE [NewOrders] ( [OrderID] [int] NOT NULL , [CustomerID] [nchar] (5) NULL , [EmployeeID] [int] NULL , [OrderDate] [datetime] NULL , [RequiredDate] [datetime] NULL , [ShippedDate] [datetime] NULL , [ShipVia] [int] NULL , [Freight] [money] NULL , [ShipName] [nvarchar] (40) NULL, [ShipAddress] [nvarchar] (60) , [ShipCity] [nvarchar] (15) NULL, [ShipRegion] [nvarchar] (15) NULL, [ShipPostalCode] [nvarchar] (10) NULL, [ShipCountry] [nvarchar] (15) NULL ) INSERT into NewOrders SELECT * FROM Orders 2. Build nc index on OrderDate: create index dateindex on neworders(orderdate) 3. Test Query by looking at query plan: select orderdate from NewOrders The index is being scanned, as expected. 4. Build an index on orderId: create index orderid_index on neworders(orderID) 5. Test Query by looking at query plan: select orderdate from NewOrders Now the TABLE is being scanned, instead of the original index! Index Intersection Multiple Indexes Can Be Used On A Single Table In versions prior to SQL Server 7, only one index could be used for any table to process any single query. The only exception was a query involving an OR. In current SQL Server versions, multiple nonclustered indexes can each be accessed, retrieving a set of keys with bookmarks, and then the result sets can be joined on the common bookmarks. The optimizer weighs the cost of performing the unindexed join on the intermediate result sets, with the cost of only using one index, and then scanning the entire result set from that single index. Fillfactor and Performance Creating an Index with a Low Fillfactor Delays Page Splits when Inserting DBCC SHOWCONTIG will show you a low value for “Avg. Page Density” when a low fillfactor has been specified. This is good for inserts and updates, because it will delay the need to split pages to make room for new rows. It can be bad for scans, because fewer rows will be on each page, and more pages must be read to access the same amount of data. However, this cost will be minimal if the scan density value is good. Index Reorganization DBCC SHOWCONTIG Provides Lots of Information Here’s some sample output from running a basic DBCC SHOWCONTIG on the order details table in the Northwind database: DBCC SHOWCONTIG scanning 'Order Details' table... Table: 'Order Details' (325576198); index ID: 1, database ID:6 TABLE level scan performed. - Pages Scanned................................: 9 - Extents Scanned..............................: 6 - Extent Switches..............................: 5 - Avg. Pages per Extent........................: 1.5 - Scan Density [Best Count:Actual Count].......: 33.33% [2:6] - Logical Scan Fragmentation ..................: 0.00% - Extent Scan Fragmentation ...................: 16.67% - Avg. Bytes Free per Page.....................: 673.2 - Avg. Page Density (full).....................: 91.68% By default, DBCC SHOWCONTIG scans the page chain at the leaf level of the specified index and keeps track of the following values:  Average number of bytes free on each page (Avg. Bytes Free per Page)  Number of pages accessed (Pages scanned)  Number of extents accessed (Extents scanned)  Number of times a page had a lower page number than the previous page in the scan (This value for Out of order pages is not displayed, but is used for additional computations.)  Number of times a page in the scan was on a different extent than the previous page in the scan (Extent switches) SQL Server also keeps track of all the extents that have been accessed, and then it determines how many gaps are in the used extents. An extent is identified by the page number of its first page. So, if extents 8, 16, 24, 32, and 40 make up an index, there are no gaps. If the extents are 8, 16, 24, and 40, there is one gap. The value in DBCC SHOWCONTIG’s output called Extent Scan Fragmentation is computed by dividing the number of gaps by the number of extents, so in this example the Extent Scan Fragmentation is ¼, or 25 percent. A table using extents 8, 24, 40, and 56 has three gaps, and its Extent Scan Fragmentation is ¾, or 75 percent. The maximum number of gaps is the number of extents - 1, so Extent Scan Fragmentation can never be 100 percent. The value in DBCC SHOWCONTIG’s output called Logical Scan Fragmentation is computed by dividing the number of Out of order pages by the number of pages in the table. This value is meaningless in a heap. You can use either the Extent Scan Fragmentation value or the Logical Scan Fragmentation value to determine the general level of fragmentation in a table. The lower the value, the less fragmentation there is. Alternatively, you can use the value called Scan Density, which is computed by dividing the optimum number of extent switches by the actual number of extent switches. A high value means that there is little fragmentation. Scan Density is not valid if the table spans multiple files; therefore, it is less useful than the other values. SQL Server 2000 allows online defragmentation You can choose from several methods for removing fragmentation from an index. You could rebuild the index and have SQL Server allocate all new contiguous pages for you. To rebuild the index, you can use a simple DROP INDEX and CREATE INDEX combination, but in many cases using these commands is less than optimal. In particular, if the index is supporting a constraint, you cannot use the DROP INDEX command. Alternatively, you can use DBCC DBREINDEX, which can rebuild all the indexes on a table in one operation, or you can use the drop_existing clause along with CREATE INDEX. The drawback of these methods is that the table is unavailable while SQL Server is rebuilding the index. When you are rebuilding only nonclustered indexes, SQL Server takes a shared lock on the table, which means that users cannot make modifications, but other processes can SELECT from the table. Of course, those SELECT queries cannot take advantage of the index you are rebuilding, so they might not perform as well as they would otherwise. If you are rebuilding a clustered index, SQL Server takes an exclusive lock and does not allow access to the table, so your data is temporarily unavailable. SQL Server 2000 lets you defragment an index without completely rebuilding it. DBCC INDEXDEFRAG reorders the leaf-level pages into physical order as well as logical order, but using only the pages that are already allocated to the leaf level. This command does an in-place ordering, which is similar to a sorting technique called bubble sort (you might be familiar with this technique if you've studied and compared various sorting algorithms). In-place ordering can reduce logical fragmentation to 2 percent or less, making an ordered scan through the leaf level much faster. DBCC INDEXDEFRAG also compacts the pages of an index, based on the original fillfactor. The pages will not always end up with the original fillfactor, but SQL Server uses that value as a goal. The defragmentation process attempts to leave at least enough space for one average-size row on each page. In addition, if SQL Server cannot obtain a lock on a page during the compaction phase of DBCC INDEXDEFRAG, it skips the page and does not return to it. Any empty pages created as a result of compaction are removed. The algorithm SQL Server 2000 uses for DBCC INDEXDEFRAG finds the next physical page in a file belonging to the index's leaf level and the next logical page in the leaf level to swap it with. To find the next physical page, the algorithm scans the IAM pages belonging to that index. In a database spanning multiple files, in which a table or index has pages on more than one file, SQL Server handles pages on different files separately. SQL Server finds the next logical page by scanning the index's leaf level. After each page move, SQL Server drops all locks and saves the last key on the last page it moved. The next iteration of the algorithm uses the last key to find the next logical page. This process lets other users update the table and index while DBCC INDEXDEFRAG is running. Let us look at an example in which an index's leaf level consists of the following pages in the following logical order: 47 22 83 32 12 90 64 The first key is on page 47, and the last key is on page 64. SQL Server would have to scan the pages in this order to retrieve the data in sorted order. As its first step, DBCC INDEXDEFRAG would find the first physical page, 12, and the first logical page, 47. It would then swap the pages, using a temporary buffer as a holding area. After the first swap, the leaf level would look like this: 12 22 83 32 47 90 64 The next physical page is 22, which is also the next logical page, so no work would be necessary. DBCC INDEXDEFRAG would then swap the next physical page, 32, with the next logical page, 83: 12 22 32 83 47 90 64 After the next swap of 47 with 83, the leaf level would look like this: 12 22 32 47 83 90 64 Then, the defragmentation process would swap 64 with 83: 12 22 32 47 64 90 83 and 83 with 90: 12 22 32 47 64 83 90 At the end of the DBCC INDEXDEFRAG operation, the pages in the table or index are not contiguous, but their logical order matches their physical order. Now, if the pages were accessed from disk in sorted order, the head would need to move in only one direction. Keep in mind that DBCC INDEXDEFRAG uses only pages that are already part of the index's leaf level; it allocates no new pages. In addition, defragmenting a large table can take quite a while, and you will get a report every 5 minutes about the estimated percentage completed. However, except for the locks on the pages being switched, this command needs no additional locks. All the table's other pages and indexes are fully available for your applications to use during the defragmentation process. If you must completely rebuild an index because you want a new fillfactor, or if simple defragmentation is not enough because you want to remove all fragmentation from your indexes, another SQL Server 2000 improvement makes index rebuilding less of an imposition on the rest of the system. SQL Server 2000 lets you create an index in parallel—that is, using multiple processors—which drastically reduces the time necessary to perform the rebuild. The algorithm SQL Server 2000 uses, allows near-linear scaling with the number of processors you use for the rebuild, so four processors will take only one-fourth the time that one processor requires to rebuild an index. System availability increases because the length of time that a table is unavailable decreases. Note that only the SQL Server 2000 Enterprise Edition supports parallel index creation. Indexes on Views and Computed Columns Building an Index Gives the Data Physical Existence Normally, views are only logical and the rows comprising the view’s data are not generated until the view is accessed. The values for computed columns are typically not stored anywhere in the database; only the definition for the computation is stored and the computation is redone every time a computed column is accessed. The first index on a view must be a clustered index, so that the leaf level can hold all the actual rows that make up the view. Once that clustered index has been build, and the view’s data is now physical, additional (nonclustered) indexes can be built. An index on a computed column can be nonclustered, because all we need to store is the index key values. Common Prerequisites for Indexed Views and Indexes on Computed Columns In order for SQL Server to create use these special indexes, you must have the seven SET options correctly specified: ARITHABORT, CONCAT_NULL_YIELDS_NULL, QUOTED_IDENTIFIER, ANSI_NULLS, ANSI_PADDING, ANSI_WARNING must be all ON NUMERIC_ROUNDABORT must be OFF Only deterministic expressions can be used in the definition of Indexed Views or indexes on Computed Columns. See the BOL for the list of deterministic functions and expressions. Property functions are available to check if a column or view meets the requirements and is indexable. SELECT OBJECTPROPERTY (Object_id, ‘IsIndexable’) SELECT COLUMNPROPERTY (Object_id, column_name , ‘IsIndexable’ ) Schema Binding Guarantees That Object Definition Won’t Change A view can only be indexed if it has been built with schema binding. The SQL Server Optimizer Determines If the Indexed View Can Be Used The query must request a subset of the data contained in the view. The ability of the optimizer to use the indexed view even if the view is not directly referenced is available only in SQL Server 2000 Enterprise Edition. In Standard edition, you can create indexed views, and you can select directly from them, but the optimizer will not choose to use them if they are not directly referenced. Examples of Indexed Views: The best candidates for improvement by indexed views are queries performing aggregations and joins. We will explain how the useful indexed views may be created for these two major groups of queries. The considerations are valid also for queries and indexed views using both joins and aggregations. -- Example: USE Northwind -- Identify 5 products with overall biggest discount total. -- This may be expressed for example by two different queries: -- Q1. select TOP 5 ProductID, SUM(UnitPrice*Quantity)- SUM(UnitPrice*Quantity*(1.00-Discount)) Rebate from [order details] group by ProductID order by Rebate desc --Q2. select TOP 5 ProductID, SUM(UnitPrice*Quantity*Discount) Rebate from [order details] group by ProductID order by Rebate desc --The following indexed view will be used to execute Q1. create view Vdiscount1 with schemabinding as select SUM(UnitPrice*Quantity) SumPrice, SUM(UnitPrice*Quantity*(1.00-Discount)) SumDiscountPrice, COUNT_BIG(*) Count, ProductID from dbo.[order details] group By ProductID create unique clustered index VDiscountInd on Vdiscount1 (ProductID) However, it will not be used by the Q2 because the indexed view does not contain the SUM(UnitPrice*Quantity*Discount) aggregate. We can construct another indexed view create view Vdiscount2 with schemabinding as select SUM(UnitPrice*Quantity) SumPrice, SUM(UnitPrice*Quantity*(1.00-Discount)) SumDiscountPrice, SUM(UnitPrice*Quantity*Discount) SumDiscoutPrice2, COUNT_BIG(*) Count, ProductID from dbo.[order details] group By ProductID create unique clustered index VDiscountInd on Vdiscount2 (ProductID) This view may be used by both Q1 and Q2. Observe that the indexed view Vdiscount2 will have the same number of rows and only one more column compared to Vdiscount1, and it may be used by more queries. In general, try to design indexed views that may be used by more queries. The following query asking for the order with the largest total discount -- Q3. select TOP 3 OrderID, SUM(UnitPrice*Quantity*Discount) OrderRebate from dbo.[order details] group By OrderID Q3 can use neither of the Vdiscount views because the column OrderID is not included in the view definition. To address this variation of the discount analysis query we may create a different indexed view, similar to the query itself. An attempt to generalize the previous indexed view Vdiscount2 so that all three queries Q1, Q2, and Q3 can take advantage of a single indexed view would require a view with both OrderID and ProductID as grouping columns. Because the OrderID, ProductID combination is unique in the original order details table the resulting view would have as many rows as the original table and we would see no savings in using such view compared to using the original table. Consider the size of the resulting indexed view. In the case of pure aggregation, the indexed view may provide no significant performance gains if its size is close to the size of the original table. Complex aggregates (STDEV, VARIANCE, AVG) cannot participate in the index view definition. However, SQL Server may use an indexed view to execute a query containing AVG aggregate. Query containing STDEV or VARIANCE cannot use indexed view to pre-compute these values. The next example shows a query producing the average price for a particular product -- Q4. select ProductName, od.ProductID, AVG(od.UnitPrice*(1.00-Discount)) AvgPrice, SUM(od.Quantity) Units from [order details] od, Products p where od.ProductID=p.ProductID group by ProductName, od.ProductID This is an example of indexed view that will be considered by the SQL Server to answer the Q4 create view v3 with schemabinding as select od.ProductID, SUM(od.UnitPrice*(1.00-Discount)) Price, COUNT_BIG(*) Count, SUM(od.Quantity) Units from dbo.[order details] od group by od.ProductID go create UNIQUE CLUSTERED index iv3 on v3 (ProductID) go Observe that the view definition does not contain the table Products. The indexed view does not need to contain all tables used in the query that uses the indexed view. In addition, the following query (same as above Q4 only with one additional search condition) will use the same indexed view. Observe that the added predicate references only columns from tables not present in the v3 view definition. -- Q5. select ProductName, od.ProductID, AVG(od.UnitPrice*(1.00-Discount)) AvgPrice, SUM(od.Quantity) Units from [order details] od, Products p where od.ProductID=p.ProductID and p.ProductName like '%tofu%' group by ProductName, od.ProductID The following query cannot use the indexed view because the added search condition od.UnitPrice>10 contains a column from the table in the view definition and the column is neither grouping column nor the predicate appears in the view definition. -- Q6. select ProductName, od.ProductID, AVG(od.UnitPrice*(1.00-Discount)) AvgPrice, SUM(od.Quantity) Units from [order details] od, Products p where od.ProductID=p.ProductID and od.UnitPrice>10 group by ProductName, od.ProductID To contrast the Q6 case, the following query will use the indexed view v3 since the added predicate is on the grouping column of the view v3. -- Q7. select ProductName, od.ProductID, AVG(od.UnitPrice*(1.00-Discount)) AvgPrice, SUM(od.Quantity) Units from [order details] od, Products p where od.ProductID=p.ProductID and od.ProductID in (1,2,13,41) group by ProductName, od.ProductID -- The previous query Q6 will use the following indexed view V4: create view V4 with schemabinding as select ProductName, od.ProductID, SUM(od.UnitPrice*(1.00-Discount)) AvgPrice, SUM(od.Quantity) Units, COUNT_BIG(*) Count from dbo.[order details] od, dbo.Products p where od.ProductID=p.ProductID and od.UnitPrice>10 group by ProductName, od.ProductID create unique clustered index VDiscountInd on V4 (ProductName, ProductID) The same index on the view V4 will be used also for a query where a join to the table Orders is added, for example -- Q8. select ProductName, od.ProductID, AVG(od.UnitPrice*(1.00-Discount)) AvgPrice, SUM(od.Quantity) Units from dbo.[order details] od, dbo.Products p, dbo.Orders o where od.ProductID=p.ProductID and o.OrderID=od.OrderID and od.UnitPrice>10 group by ProductName, od.ProductID We will show several modifications of the query Q8 and explain why such modifications cannot use the above view V4. -- Q8a. select ProductName, od.ProductID, AVG(od.UnitPrice*(1.00-Discount)) AvgPrice, SUM(od.Quantity) Units from dbo.[order details] od, dbo.Products p, dbo.Orders o where od.ProductID=p.ProductID and o.OrderID=od.OrderID and od.UnitPrice>25 group by ProductName, od.ProductID 8a cannot use the indexed view because of the where clause mismatch. Observe that table Orders does not participate in the indexed view V4 definition. In spite of that, adding a predicate on this table will disallow using the indexed view because the added predicate may eliminate additional rows participating in the aggregates as it is shown in Q8b. -- Q8b. select ProductName, od.ProductID, AVG(od.UnitPrice*(1.00-Discount)) AvgPrice, SUM(od.Quantity) Units from dbo.[order details] od, dbo.Products p, dbo.Orders o where od.ProductID=p.ProductID and o.OrderID=od.OrderID and od.UnitPrice>10 and o.OrderDate>'01/01/1998' group by ProductName, od.ProductID Locking and Indexes In General, You Should Let SQL Server Control the Locking within Indexes The stored procedure sp_indexoption lets you manually control the unit of locking within an index. It also lets you disallow page locks or row locks within an index. Since these options are available only for indexes, there is no way to control the locking within the data pages of a heap. (But remember that if a table has a clustered index, the data pages are part of the index and are affected by the sp_indexoption setting.) The index options are set for each table or index individually. Two options, Allow Rowlocks and AllowPageLocks, are both set to TRUE initially for every table and index. If both of these options are set to FALSE for a table, only full table locks are allowed. As described in Module 4, SQL Server determines at runtime whether to initially lock rows, pages, or the entire table. The locking of rows (or keys) is heavily favored. The type of locking chosen is based on the number of rows and pages to be scanned, the number of rows on a page, the isolation level in effect, the update activity going on, the number of users on the system needing memory for their own purposes, and so on. SAP databases frequently use sp_indexoption to reduce deadlocks Setting vs. Querying In SQL Server 2000, the procedure sp_indexoption should only be used for setting an index option. To query an option, use the INDEXPROPERTY function. Lesson 2: Concepts – Statistics Statistics are the most important tool that the SQL Server query optimizer has to determine the ideal execution plan for a query. Statistics that are out of date or nonexistent seriously jeopardize query performance. SQL Server 2000 computes and stores statistics in a completely different format that all earlier versions of SQL Server. One of the improvements is an increased ability to determine which values are out of the normal range in terms of the number of occurrences. The new statistics maintenance routines are particularly good at determining when a key value has a very unusual skew of data. What You Will Learn After completing this lesson, you will be able to:  Define terms related to statistics collected by SQL Server.  Describe how statistics are maintained by SQL Server.  Discuss the autostats feature of SQL Server.  Describe how statistics are used in query optimization. Recommended Reading  Statistics Used by the Query Optimizer in Microsoft SQL Server 2000 http://msdn.microsoft.com/library/techart/statquery.htm Definitions Cardinality The cardinality means how many unique values exist in the data. Density For each index and set of column statistics, SQL Server keeps track of details about the uniqueness (or density) of the data values encountered, which provides a measure of how selective the index is. A unique index, of course, has the lowest density —by definition, each index entry can point to only one row. A unique index has a density value of 1/number of rows in the table. Density values range from 0 through 1. Highly selective indexes have density values of 0.10 or lower. For example, a unique index on a table with 8345 rows has a density of 0.00012 (1/8345). If a nonunique nonclustered index has a density of 0.2165 on the same table, each index key can be expected to point to about 1807 rows (0.2165 × 8345). This is probably not selective enough to be more efficient than just scanning the table, so this index is probably not useful. Because driving the query from a nonclustered index means that the pages must be retrieved in index order, an estimated 1807 data page accesses (or logical reads) are needed if there is no clustered index on the table and the leaf level of the index contains the actual RID of the desired data row. The only time a data page doesn’t need to be reaccessed is when the occasional coincidence occurs in which two adjacent index entries happen to point to the same data page. In general, you can think of density as the average number of duplicates. We can also talk about the term ‘join density’, which applies to the average number of duplicates in the foreign key column. This would answer the question: in this one-to-many relationship, how many is ‘many’? Selectivity In general selectivity applies to a particular data value referenced in a WHERE clause. High selectivity means that only a small percentage of the rows satisfy the WHERE clause filter, and a low selectivity means that many rows will satisfy the filter. For example, in an employees table, the column employee_id is probably very selective, and the column gender is probably not very selective at all. Statistics Statistics are a histogram consisting of an even sampling of values for a column or for an index key (or the first column of the key for a composite index) based on the current data. The histogram is stored in the statblob field of the sysindexes table, which is of type image. (Remember that image data is actually stored in structures separate from the data row itself. The data row merely contains a pointer to the image data. For simplicity’s sake, we’ll talk about the index statistics as being stored in the image field called statblob.) To fully estimate the usefulness of an index, the optimizer also needs to know the number of pages in the table or index; this information is stored in the dpages column of sysindexes. During the second phase of query optimization, index selection, the query optimizer determines whether an index exists for a columns in your WHERE clause, assesses the index’s usefulness by determining the selectivity of the clause (that is, how many rows will be returned), and estimates the cost of finding the qualifying rows. Statistics for a single column index consist of one histogram and one density value. The multicolumn statistics for one set of columns in a composite index consist of one histogram for the first column in the index and density values for each prefix combination of columns (including the first column alone). The fact that density information is kept for all columns helps the optimizer decide how useful the index is for joins. Suppose, for example, that an index is composed of three key fields. The density on the first column might be 0.50, which is not too useful. However, as you look at more key columns in the index, the number of rows pointed to is fewer than (or in the worst case, the same as) the first column, so the density value goes down. If you are looking at both the first and second columns, the density might be 0.25, which is somewhat better. Moreover, if you examine three columns, the density might be 0.03, which is highly selective. It does not make sense to refer to the density of only the second column. The lead column density is always needed. Statistics Maintenance Statistics Information Tracks the Distribution of Key Values SQL Server statistics is basically a histogram that contains up to 200 values of a given key column. In addition to the histogram, the statblob field contains the following information:  The time of the last statistics collection  The number of rows used to produce the histogram and density information  The average key length  Densities for other combinations of columns In the statblob column, up to 200 sample values are stored; the range of key values between each sample value is called a step. The sample value is the endpoint of the range. Three values are stored along with each step: a value called EQ_ROWS, which is the number of rows that have a value equal to that sample value; a value called RANGE_ROWS, which specifies how many other values are inside the range (between two adjacent sample values); and the number of distinct values, or RANGE_DENSITY of the range. DBCC SHOW_STATISTICS The DBCC SHOW_STATISTICS output shows us the first two of these three values, but not the range density. The RANGE_DENSITY is instead used to compute two additional values:  DISTINCT_RANGE_ROWS—the number of distinct rows inside this range (not counting the RANGE_HI_KEY value itself. This is computed as 1/RANGE_DENSITY.  AVG_RANGE_ROWS—the average number of rows per distinct value, computed as RANGE_DENSITY * RANGE_ROWS. In addition to statistics on indexes, SQL Server can also keep track of statistics on columns with no indexes. Knowing the density, or the likelihood of a particular value occurring, can help the optimizer determine an optimum processing strategy, even if SQL Server can’t use an index to actually locate the values. Statistics on Columns Column statistics can be useful for two main purposes  When the SQL Server optimizer is determining the optimal join order, it frequently is best to have the smaller input processed first. By ‘input’ we mean table after all filters in the WHERE clause have been applied. Even if there is no useful index on a column in the WHERE clause, statistics could tell us that only a few rows will quality, and those the resulting input will be very small.  The SQL Server query optimizer can use column statistics on non-initial columns in a composite nonclustered index to determine if scanning the leaf level to obtain the bookmarks will be an efficient processing strategy. For example, in the member table in the credit database, the first name column is almost unique. Suppose we have a nonclustered index on (lastname, firstname), and we issue this query: select * from member where firstname = 'MPRO' In this case, statistics on the firstname column would indicate very few rows satisfying this condition, so the optimizer will choose to scan the nonclustered index, since it is smaller than the clustered index (the table). The small number of bookmarks will then be followed to retrieve the actual data. Manually Updating Statistics You can also manually force statistics to be updated in one of two ways. You can run the UPDATE STATISTICS command on a table or on one specific index or column statistics, or you can also execute the procedure sp_updatestats, which runs UPDATE STATISTICS against all user-defined tables in the current database. You can create statistics on unindexed columns using the CREATE STATISTICS command or by executing sp_createstats, which creates single-column statistics for all eligible columns for all user tables in the current database. This includes all columns except computed columns and columns of the ntext, text, or image datatypes, and columns that already have statistics or are the first column of an index. Autostats By Default SQL Server Will Update Statistics on Any Index or Column as Needed Every database is created with the database options auto create statistics and auto update statistics set to true, but you can turn either one off. You can also turn off automatic updating of statistics for a specific table in one of two ways:  UPDATE STATISTICS In addition to updating the statistics, the option WITH NORECOMPUTE indicates that the statistics should not be automatically recomputed in the future. Running UPDATE STATISTICS again without the WITH NORECOMPUTE option enables automatic updates.  sp_autostats This procedure sets or unsets a flag for a table to indicate that statistics should or should not be updated automatically. You can also use this procedure with only the table name to find out whether the table is set to automatically have its index statistics updated. ' However, setting the database option auto update statistics to FALSE overrides any individual table settings. In other words, no automatic updating of statistics takes place. This is not a recommended practice unless thorough testing has shown you that you do not need the automatic updates or that the performance overhead is more than you can afford. Trace Flags Trace flag 205 – reports recompile due to autostats. Trace flag 8721 – writes information to the errorlog when AutoStats has been run. For more information, see the following Knowledge Base article: Q195565 “INF: How SQL Server 7.0 Autostats Work.” Statistics and Performance The Performance Penalty of NOT Having Up-To-Date Statistics Far Outweighs the Benefit of Avoiding Automatic Updating Autostats should be turned off only after thorough testing shows it to be necessary. Because autostats only forces a recompile after a certain number or percentage of rows has been changed, you do not have to make any adjustments for a read-only database. Lesson 3: Concepts – Query Optimization What You Will Learn After completing this lesson, you will be able to:  Describe the phases of query optimization.  Discuss how SQL Server estimates the selectivity of indexes and column and how this estimate is used in query optimization. Recommended Reading  Chapter 15: “The Query Processor”, Inside SQL Server 2000 by Kalen Delaney  Chapter 16: “Query Tuning”, Inside SQL Server 2000 by Kalen Delaney  Whitepaper about SQL Server Query Processor Architecture by Hal Berenson and Kalen Delaney http://msdn.microsoft.com/library/backgrnd/html/sqlquerproc.htm Phases of Query Optimization Query Optimization Involves several phases Trivial Plan Optimization Optimization itself goes through several steps. The first step is something called Trivial Plan Optimization. The whole idea of trivial plan optimization is that cost based optimization is a bit expensive to run. The optimizer can try a great many possible variations trying to find the cheapest plan. If SQL Server knows that there is only one really viable plan for a query, it could avoid a lot of work. A prime example is a query that consists of an INSERT with a VALUES clause. There is only one possible plan. Another example is a SELECT where all the columns are in a unique covering index, and that index is the only one that is useable. There is no other index that has that set of columns in it. These two examples are cases where SQL Server should just generate the plan and not try to find something better. The trivial plan optimizer finds the really obvious plans, which are typically very inexpensive. In fact, all the plans that get through the autoparameterization template result in plans that the trivial plan optimizer can find. Between those two mechanisms, the plans that are simple tend to be weeded out earlier in the process and do not pay a lot of the compilation cost. This is a good thing, because the number of potential plans in 7.0 went up astronomically as SQL Server added hash joins, merge joins and index intersections, to its list of processing techniques. Simplification and Statistics Loading If a plan is not found by the trivial plan optimizer, SQL Server can perform some simplifications, usually thought of as syntactic transformations of the query itself, looking for commutative properties and operations that can be rearranged. SQL Server can do constant folding, and other operations that do not require looking at the cost or analyzing what indexes are, but that can result in a more efficient query. SQL Server then loads up the metadata including the statistics information on the indexes, and then the optimizer goes through a series of phases of cost based optimization. Cost Based Optimization Phases The cost based optimizer is designed as a set of transformation rules that try various permutations of indexes and join strategies. Because of the number of potential plans in SQL Server 7.0 and SQL Server 2000, if the optimizer just ran through all the combinations and produced a plan, the optimization process would take a very long time to run. Therefore, optimization is broken up into phases. Each phase is a set of rules. After each phase is run, the cost of any resulting plan is examined, and if SQL Server determines that the plan is cheap enough, that plan is kept and executed. If the plan is not cheap enough, the optimizer runs the next phase, which is another set of rules. In the vast majority of cases, a good plan will be found in the preliminary phases. Typically, if the plan that a query would have had in SQL Server 6.5 is also the optimal plan in SQL Server 7.0 and SQL Server 2000, the plan will tend to be found either by the trivial plan optimizer or by the first phase of the cost based optimizer. The rules were intentionally organized to try to make that be true. The plan will probably consist of using a single index and using nested loops. However, every once in a while, because of lack of statistical information, or some other nuance, the optimizer will have to proceed with the later phases of optimization. Sometimes this is because there is a real possibility that the optimizer could find a better plan. When a plan is found, it becomes the optimizer’s output, and then SQL Server goes through all the caching mechanisms that we have already discussed in Module 5. Full Optimization At some point, the optimizer determines that it has gone through enough preliminary phases, and it reverts to a phase called full optimization. If the optimizer goes through all the preliminary phases, and still has not found a cheap plan, it examines the cost for the plan that it has so far. If the cost is above the threshold, the optimizer goes into a phase called full optimization. This threshold is configurable, as the configuration option ‘cost threshold for parallelism’. The full optimization phase assumes that this plan should be run this in parallel. If the machine is very busy, the plan will end up running it in serial, but the optimizer has a goal to produce a good parallel. If the cost is below the threshold (or a single processor machine), the full optimization phase just uses a brute force method to find a serial plan. Selectivity Estimation Selectivity Is One of The Most Important Pieces of Information One of the most import things the optimizer needs to know is the number of rows from any table that will meet all the conditions in the query. If there are no restrictions on a table, and all the rows will be needed, the optimizer can determine the number of rows from the sysindexes table. This number is not absolutely guaranteed to be accurate, but it is the number the optimizer uses. If there is a filter on the table in a WHERE clause, the optimizer needs statistics information. Indexes automatically maintain statistics, and the optimizer will use these values to determine the usefulness of the index. If there is no index on the column involved in the filter, then column statistics can be used or generated. Optimizing Search Arguments In General, the Filters in the WHERE Clause Determine Which Indexes Will Be Useful If an indexed column is referenced in a Search Argument (SARG), the optimizer will analyze the cost of using that index. A SARG has the form:  column value  value column  Operator must be one of =, >, >= <, <= The value can be a constant, an operation, or a variable. Some functions also will be treated as SARGs. These queries have SARGs, and a nonclustered index on firstname will be used in most cases: select * from member where firstname < 'AKKG' select * from member where firstname = substring('HAAKGALSFJA', 2,5) select * from member where firstname = 'AA' + 'KG' declare @name char(4) set @name = 'AKKG' select * from member where firstname < @name Not all functions can be used in SARGs. select * from charge where charge_amt < 2*2 select * from charge where charge_amt < sqrt(16) Compare these queries to ones using = instead of <. With =, the optimizer can use the density information to come up with a good row estimate, even if it’s not going to actually perform the function’s calculations. A filter with a variable is usually a SARG The issue is, can the optimizer come up with useful costing information? A filter with a variable is not a SARG if the variable is of a different datatype, and the column must be converted to the variable’s datatype For more information, see the following Knowledge Base article: Q198625 Enter Title of KB Article Here Use credit go CREATE TABLE [member2] ( [member_no] [smallint] NOT NULL , [lastname] [shortstring] NOT NULL , [firstname] [shortstring] NOT NULL , [middleinitial] [letter] NULL , [street] [shortstring] NOT NULL , [city] [shortstring] NOT NULL , [state_prov] [statecode] NOT NULL , [country] [countrycode] NOT NULL , [mail_code] [mailcode] NOT NULL ) GO insert into member2 select member_no, lastname, firstname, middleinitial, street, city, state_prov, country, mail_code from member alter table member2 add constraint pk_member2 primary key clustered (lastname, member_no, firstname, country) declare @id int set @id = 47 update member2 set city = city + ' City', state_prov = state_prov + ' State' where lastname = 'Barr' and member_no = @id and firstname = 'URQYJBFVRRPWKVW' and country = 'USA' These queries don’t have SARGs, and a table scan will be done: select * from member where substring(lastname, 1,2) = ‘BA’ Some non-SARGs can be converted select * from member where lastname like ‘ba%’ In some cases, you can rewrite your query to turn a non-SARG into a SARG; for example, you can rewrite the substring query above and the LIKE query that follows it. Join Order and Types of Joins Join Order and Strategy Is Determined By the Optimizer The execution plan output will display the join order from top to bottom; i.e. the table listed on top is the first one accessed in a join. You can override the optimizer’s join order decision in two ways:  OPTION (FORCE ORDER) applies to one query  SET FORCEPLAN ON applies to entire session, until set OFF If either of these options is used, the join order is determined by the order the tables are listed in the query’s FROM clause, and no optimizer on JOIN ORDER is done. Forcing the JOIN order may force a particular join strategy. For example, in most outer join operations, the outer table is processed first, and a nested loops join is done. However, if you force the inner table to be accessed first, a merge join will need to be done. Compare the query plan for this query with and without the FORCE ORDER hint: select * from titles right join publishers on titles.pub_id = publishers.pub_id -- OPTION (FORCE ORDER) Nested Loop Join A nested iteration is when the query optimizer constructs a set of nested loops, and the result set grows as it progresses through the rows. The query optimizer performs the following steps. 1. Finds a row from the first table. 2. Uses that row to scan the next table. 3. Uses the result of the previous table to scan the next table. Evaluating Join Combinations The query optimizer automatically evaluates at least four or more possible join combinations, even if those combinations are not specified in the join predicate. You do not have to add redundant clauses. The query optimizer balances the cost and uses statistics to determine the number of join combinations that it evaluates. Evaluating every possible join combination is inefficient and costly. Evaluating Cost of Query Performance When the query optimizer performs a nested join, you should be aware that certain costs are incurred. Nested loop joins are far superior to both merge joins and hash joins when executing small transactions, such as those affecting only a small set of rows. The query optimizer:  Uses nested loop joins if the outer input is quite small and the inner input is indexed and quite large.  Uses the smaller input as the outer table.  Requires that a useful index exist on the join predicate for the inner table.  Always uses a nested loop join strategy if the join operation uses an operator other than an equality operator. Merge Joins The columns of the join conditions are used as inputs to process a merge join. SQL Server performs the following steps when using a merge join strategy: 1. Gets the first input values from each input set. 2. Compares input values. 3. Performs a merge algorithm. • If the input values are equal, the rows are returned. • If the input values are not equal, the lower value is discarded, and the next input value from that input is used for the next comparison. 4. Repeats the process until all of the rows from one of the input sets have been processed. 5. Evaluates any remaining search conditions in the query and returns only rows that qualify. Note Only one pass per input is done. The merge join operation ends after all of the input values of one input have been evaluated. The remaining values from the other input are not processed. Requires That Joined Columns Are Sorted If you execute a query with join operations, and the joined columns are in sorted order, the query optimizer processes the query by using a merge join strategy. A merge join is very efficient because the columns are already sorted, and it requires fewer page I/O. Evaluates Sorted Values For the query optimizer to use the merge join, the inputs must be sorted. The query optimizer evaluates sorted values in the following order: 1. Uses an existing index tree (most typical). The query optimizer can use the index tree from a clustered index or a covered nonclustered index. 2. Leverages sort operations that the GROUP BY, ORDER BY, and CUBE clauses use. The sorting operation only has to be performed once. 3. Performs its own sort operation in which a SORT operator is displayed when graphically viewing the execution plan. The query optimizer does this very rarely. Performance Considerations Consider the following facts about the query optimizer's use of the merge join:  SQL Server performs a merge join for all types of join operations (except cross join or full join operations), including UNION operations.  A merge join operation may be a one-to-one, one-to-many, or many-to-many operation. If the merge join is a many-to-many operation, SQL Server uses a temporary table to store the rows. If duplicate values from each input exist, one of the inputs rewinds to the start of the duplicates as each duplicate value from the other input is processed.  Query performance for a merge join is very fast, but the cost can be high if the query optimizer must perform its own sort operation. If the data volume is large and the desired data can be obtained presorted from existing Balanced-Tree (B-Tree) indexes, merge join is often the fastest join algorithm.  A merge join is typically used if the two join inputs have a large amount of data and are sorted on their join columns (for example, if the join inputs were obtained by scanning sorted indexes).  Merge join operations can only be performed with an equality operator in the join predicate. Hashing is a strategy for dividing data into equal sets of a manageable size based on a given property or characteristic. The grouped data can then be used to determine whether a particular data item matches an existing value. Note Duplicate data or ranges of data are not useful for hash joins because the data is not organized together or in order. When a Hash Join Is Used The query optimizer uses a hash join option when it estimates that it is more efficient than processing queries by using a nested loop or merge join. It typically uses a hash join when an index does not exist or when existing indexes are not useful. Assigns a Build and Probe Input The query optimizer assigns a build and probe input. If the query optimizer incorrectly assigns the build and probe input (this may occur because of imprecise density estimates), it reverses them dynamically. The ability to change input roles dynamically is called role reversal. Build input consists of the column values from a table with the lowest number of rows. Build input creates a hash table in memory to store these values. The hash bucket is a storage place in the hash table in which each row of the build input is inserted. Rows from one of the join tables are placed into the hash bucket where the hash key value of the row matches the hash key value of the bucket. Hash buckets are stored as a linked list and only contain the columns that are needed for the query. A hash table contains hash buckets. The hash table is created from the build input. Probe input consists of the column values from the table with the most rows. Probe input is what the build input checks to find a match in the hash buckets. Note The query optimizer uses column or index statistics to help determine which input is the smaller of the two. Processing a Hash Join The following list is a simplified description of how the query optimizer processes a hash join. It is not intended to be comprehensive because the algorithm is very complex. SQL Server: 1. Reads the probe input. Each probe input is processed one row at a time. 2. Performs the hash algorithm against each probe input and generates a hash key value. 3. Finds the hash bucket that matches the hash key value. 4. Accesses the hash bucket and looks for the matching row. 5. Returns the row if a match is found. Performance Considerations Consider the following facts about the hash joins that the query optimizer uses:  Similar to merge joins, a hash join is very efficient, because it uses hash buckets, which are like a dynamic index but with less overhead for combining rows.  Hash joins can be performed for all types of join operations (except cross join operations), including UNION and DIFFERENCE operations.  A hash operator can remove duplicates and group data, such as SUM (salary) GROUP BY department. The query optimizer uses only one input for both the build and probe roles.  If join inputs are large and are of similar size, the performance of a hash join operation is similar to a merge join with prior sorting. However, if the size of the join inputs is significantly different, the performance of a hash join is often much faster.  Hash joins can process large, unsorted, non-indexed inputs efficiently. Hash joins are useful in complex queries because the intermediate results: • Are not indexed (unless explicitly saved to disk and then indexed). • Are often not sorted for the next operation in the execution plan.  The query optimizer can identify incorrect estimates and make corrections dynamically to process the query more efficiently.  A hash join reduces the need for database denormalization. Denormalization is typically used to achieve better performance by reducing join operations despite redundancy, such as inconsistent updates. Hash joins give you the option to vertically partition your data as part of your physical database design. Vertical partitioning represents groups of columns from a single table in separate files or indexes. Subquery Performance Joins Are Not Inherently Better Than Subqueries Here is an example showing three different ways to update a table, using a second table for lookup purposes. The first uses a JOIN with the update, the second uses a regular introduced with IN, and the third uses a correlated subquery. All three yield nearly identical performance. Note Note that performance comparisons cannot just be made based on I/Os. With HASHING and MERGING techniques, the number of reads may be the same for two queries, yet one may take a lot longer and use more memory resources. Also, always be sure to monitor statistics time. Suppose you want to add a 5 percent discount to order items in the Order Details table for which the supplier is Exotic Liquids, whose supplierid is 1. -- JOIN solution BEGIN TRAN UPDATE OD SET discount = discount + 0.05 FROM [Order Details] AS OD JOIN Products AS P ON OD.productid = P.productid WHERE supplierid = 1 ROLLBACK TRAN -- Regular subquery solution BEGIN TRAN UPDATE [Order Details] SET discount = discount + 0.05 WHERE productid IN (SELECT productid FROM Products WHERE supplierid = 1) ROLLBACK TRAN -- Correlated Subquery Solution BEGIN TRAN UPDATE [Order Details] SET discount = discount + 0.05 WHERE EXISTS(SELECT supplierid FROM Products WHERE [Order Details].productid = Products.productid AND supplierid = 1) ROLLBACK TRAN Internally, Your Join May Be Rewritten SQL Server’s query processor had many different ways of resolving your JOIN expressions. Subqueries may be converted to a JOIN with an implied distinct, which may result in a logical operator of SEMI JOIN. Compare the plans of the first two queries: USE credit select member_no from member where member_no in (select member_no from charge) select distinct m.member_no from member m join charge c on m.member_no = c.member_no The second query uses a HASH MATCH as the final step to remove the duplicates. The first query only had to do a semi join. For these queries, although the I/O values are the same, the first query (with the subquery) runs much faster (almost twice as fast). Another similar looking join is

[PHP] ;;;;;;;;;;;;;;;;;;; ; About php.ini ; ;;;;;;;;;;;;;;;;;;; ; PHP's initialization file, generally called php.ini, is responsible for ; configuring many of the aspects of PHP's behavior. ; PHP attempts to find and load this configuration from a number of locations. ; The following is a summary of its search order: ; 1. SAPI module specific location. ; 2. The PHPRC environment variable. (As of PHP 5.2.0) ; 3. A number of predefined registry keys on Windows (As of PHP 5.2.0) ; 4. Current working directory (except CLI) ; 5. The web server's directory (for SAPI modules), or directory of PHP ; (otherwise in Windows) ; 6. The directory from the --with-config-file-path compile time option, or the ; Windows directory (C:\windows or C:\winnt) ; See the PHP docs for more specific information. ; http://php.net/configuration.file ; The syntax of the file is extremely simple. Whitespace and lines ; beginning with a semicolon are silently ignored (as you probably guessed). ; Section headers (e.g. [Foo]) are also silently ignored, even though ; they might mean something in the future. ; Directives following the section heading [PATH=/www/mysite] only ; apply to PHP files in the /www/mysite directory. Directives ; following the section heading [HOST=www.example.com] only apply to ; PHP files served from www.example.com. Directives set in these ; special sections cannot be overridden by user-defined INI files or ; at runtime. Currently, [PATH=] and [HOST=] sections only work under ; CGI/FastCGI. ; http://php.net/ini.sections ; Directives are specified using the following syntax: ; directive = value ; Directive names are *case sensitive* - foo=bar is different from FOO=bar. ; Directives are variables used to configure PHP or PHP extensions. ; There is no name validation. If PHP can't find an expected ; directive because it is not set or is mistyped, a default value will be used. ; The value can be a string, a number, a PHP constant (e.g. E_ALL or M_PI), one ; of the INI constants (On, Off, True, False, Yes, No and None) or an expression ; (e.g. E_ALL & ~E_NOTICE), a quoted string ("bar"), or a reference to a ; previously set variable or directive (e.g. ${foo}) ; Expressions in the INI file are limited to bitwise operators and parentheses: ; | bitwise OR ; ^ bitwise XOR ; & bitwise AND ; ~ bitwise NOT ; ! boolean NOT ; Boolean flags can be turned on using the values 1, On, True or Yes. ; They can be turned off using the values 0, Off, False or No. ; An empty string can be denoted by simply not writing anything after the equal ; sign, or by using the None keyword: ; foo = ; sets foo to an empty string ; foo = None ; sets foo to an empty string ; foo = "None" ; sets foo to the string 'None' ; If you use constants in your value, and these constants belong to a ; dynamically loaded extension (either a PHP extension or a Zend extension), ; you may only use these constants *after* the line that loads the extension. ;;;;;;;;;;;;;;;;;;; ; About this file ; ;;;;;;;;;;;;;;;;;;; ; PHP comes packaged with two INI files. One that is recommended to be used ; in production environments and one that is recommended to be used in ; development environments. ; php.ini-production contains settings which hold security, performance and ; best practices at its core. But please be aware, these settings may break ; compatibility with older or less security conscience applications. We ; recommending using the production ini in production and testing environments. ; php.ini-development is very similar to its production variant, except it's ; much more verbose when it comes to errors. We recommending using the ; development version only in development environments as errors shown to ; application users can inadvertently leak otherwise secure information. ; This is php.ini-development INI file. ;;;;;;;;;;;;;;;;;;; ; Quick Reference ; ;;;;;;;;;;;;;;;;;;; ; The following are all the settings which are different in either the production ; or development versions of the INIs with respect to PHP's default behavior. ; Please see the actual settings later in the document for more details as to why ; we recommend these changes in PHP's behavior. ; display_errors ; Default Value: On ; Development Value: On ; Production Value: Off ; display_startup_errors ; Default Value: Off ; Development Value: On ; Production Value: Off ; error_reporting ; Default Value: E_ALL & ~E_NOTICE & ~E_STRICT & ~E_DEPRECATED ; Development Value: E_ALL ; Production Value: E_ALL & ~E_DEPRECATED & ~E_STRICT ; html_errors ; Default Value: On ; Development Value: On ; Production value: On ; log_errors ; Default Value: Off ; Development Value: On ; Production Value: On ; max_input_time ; Default Value: -1 (Unlimited) ; Development Value: 60 (60 seconds) ; Production Value: 60 (60 seconds) ; output_buffering ; Default Value: Off ; Development Value: 4096 ; Production Value: 4096 ; register_argc_argv ; Default Value: On ; Development Value: Off ; Production Value: Off ; request_order ; Default Value: None ; Development Value: "GP" ; Production Value: "GP" ; session.gc_divisor ; Default Value: 100 ; Development Value: 1000 ; Production Value: 1000 ; session.hash_bits_per_character ; Default Value: 4 ; Development Value: 5 ; Production Value: 5 ; short_open_tag ; Default Value: On ; Development Value: Off ; Production Value: Off ; track_errors ; Default Value: Off ; Development Value: On ; Production Value: Off ; url_rewriter.tags ; Default Value: "a=href,area=href,frame=src,form=,fieldset=" ; Development Value: "a=href,area=href,frame=src,input=src,form=fakeentry" ; Production Value: "a=href,area=href,frame=src,input=src,form=fakeentry" ; variables_order ; Default Value: "EGPCS" ; Development Value: "GPCS" ; Production Value: "GPCS" ;;;;;;;;;;;;;;;;;;;; ; php.ini Options ; ;;;;;;;;;;;;;;;;;;;; ; Name for user-defined php.ini (.htaccess) files. Default is ".user.ini" ;user_ini.filename = ".user.ini" ; To disable this feature set this option to empty value ;user_ini.filename = ; TTL for user-defined php.ini files (time-to-live) in seconds. Default is 300 seconds (5 minutes) ;user_ini.cache_ttl = 300 ;;;;;;;;;;;;;;;;;;;; ; Language Options ; ;;;;;;;;;;;;;;;;;;;; ; Enable the PHP scripting language engine under Apache. ; http://php.net/engine engine = On ; This directive determines whether or not PHP will recognize code between ; tags as PHP source which should be processed as such. It is ; generally recommended that should be used and that this feature ; should be disabled, as enabling it may result in issues when generating XML ; documents, however this remains supported for backward compatibility reasons. ; Note that this directive does not control the tags. ; http://php.net/asp-tags asp_tags = Off ; The number of significant digits displayed in floating point numbers. ; http://php.net/precision precision = 14 ; Output buffering is a mechanism for controlling how much output data ; (excluding headers and cookies) PHP should keep internally before pushing that ; data to the client. If your application's output exceeds this setting, PHP ; will send that data in chunks of roughly the size you specify. ; Turning on this setting and managing its maximum buffer size can yield some ; interesting side-effects depending on your application and web server. ; You may be able to send headers and cookies after you've already sent output ; through print or echo. You also may see performance benefits if your server is ; emitting less packets due to buffered output versus PHP streaming the output ; as it gets it. On production servers, 4096 bytes is a good setting for performance ; reasons. ; Note: Output buffering can also be controlled via Output Buffering Control ; functions. ; Possible Values: ; On = Enabled and buffer is unlimited. (Use with caution) ; Off = Disabled ; Integer = Enables the buffer and sets its maximum size in bytes. ; Note: This directive is hardcoded to Off for the CLI SAPI ; Default Value: Off ; Development Value: 4096 ; Production Value: 4096 ; http://php.net/output-buffering output_buffering = 4096 ; You can redirect all of the output of your scripts to a function. For ; example, if you set output_handler to "mb_output_handler", character ; encoding will be transparently converted to the specified encoding. ; Setting any output handler automatically turns on output buffering. ; Note: People who wrote portable scripts should not depend on this ini ; directive. Instead, explicitly set the output handler using ob_start(). ; Using this ini directive may cause problems unless you know what script ; is doing. ; Note: You cannot use both "mb_output_handler" with "ob_iconv_handler" ; and you cannot use both "ob_gzhandler" and "zlib.output_compression". ; Note: output_handler must be empty if this is set 'On' !!!! ; Instead you must use zlib.output_handler. ; http://php.net/output-handler ;output_handler = ; Transparent output compression using the zlib library ; Valid values for this option are 'off', 'on', or a specific buffer size ; to be used for compression (default is 4KB) ; Note: Resulting chunk size may vary due to nature of compression. PHP ; outputs chunks that are few hundreds bytes each as a result of ; compression. If you prefer a larger chunk size for better ; performance, enable output_buffering in addition. ; Note: You need to use zlib.output_handler instead of the standard ; output_handler, or otherwise the output will be corrupted. ; http://php.net/zlib.output-compression zlib.output_compression = Off ; http://php.net/zlib.output-compression-level ;zlib.output_compression_level = -1 ; You cannot specify additional output handlers if zlib.output_compression ; is activated here. This setting does the same as output_handler but in ; a different order. ; http://php.net/zlib.output-handler ;zlib.output_handler = ; Implicit flush tells PHP to tell the output layer to flush itself ; automatically after every output block. This is equivalent to calling the ; PHP function flush() after each and every call to print() or echo() and each ; and every HTML block. Turning this option on has serious performance ; implications and is generally recommended for debugging purposes only. ; http://php.net/implicit-flush ; Note: This directive is hardcoded to On for the CLI SAPI implicit_flush = Off ; The unserialize callback function will be called (with the undefined class' ; name as parameter), if the unserializer finds an undefined class ; which should be instantiated. A warning appears if the specified function is ; not defined, or if the function doesn't include/implement the missing class. ; So only set this entry, if you really want to implement such a ; callback-function. unserialize_callback_func = ; When floats & doubles are serialized store serialize_precision significant ; digits after the floating point. The default value ensures that when floats ; are decoded with unserialize, the data will remain the same. serialize_precision = 17 ; open_basedir, if set, limits all file operations to the defined directory ; and below. This directive makes most sense if used in a per-directory ; or per-virtualhost web server configuration file. This directive is ; *NOT* affected by whether Safe Mode is turned On or Off. ; http://php.net/open-basedir ;open_basedir = ; This directive allows you to disable certain functions for security reasons. ; It receives a comma-delimited list of function names. This directive is ; *NOT* affected by whether Safe Mode is turned On or Off. ; http://php.net/disable-functions disable_functions = ; This directive allows you to disable certain classes for security reasons. ; It receives a comma-delimited list of class names. This directive is ; *NOT* affected by whether Safe Mode is turned On or Off. ; http://php.net/disable-classes disable_classes = ; Colors for Syntax Highlighting mode. Anything that's acceptable in ; would work. ; http://php.net/syntax-highlighting ;highlight.string = #DD0000 ;highlight.comment = #FF9900 ;highlight.keyword = #007700 ;highlight.default = #0000BB ;highlight.html = #000000 ; If enabled, the request will be allowed to complete even if the user aborts ; the request. Consider enabling it if executing long requests, which may end up ; being interrupted by the user or a browser timing out. PHP's default behavior ; is to disable this feature. ; http://php.net/ignore-user-abort ;ignore_user_abort = On ; Determines the size of the realpath cache to be used by PHP. This value should ; be increased on systems where PHP opens many files to reflect the quantity of ; the file operations performed. ; http://php.net/realpath-cache-size ;realpath_cache_size = 16k ; Duration of time, in seconds for which to cache realpath information for a given ; file or directory. For systems with rarely changing files, consider increasing this ; value. ; http://php.net/realpath-cache-ttl ;realpath_cache_ttl = 120 ; Enables or disables the circular reference collector. ; http://php.net/zend.enable-gc zend.enable_gc = On ; If enabled, scripts may be written in encodings that are incompatible with ; the scanner. CP936, Big5, CP949 and Shift_JIS are the examples of such ; encodings. To use this feature, mbstring extension must be enabled. ; Default: Off ;zend.multibyte = Off ; Allows to set the default encoding for the scripts. This value will be used ; unless "declare(encoding=...)" directive appears at the top of the script. ; Only affects if zend.multibyte is set. ; Default: "" ;zend.script_encoding = ;;;;;;;;;;;;;;;;; ; Miscellaneous ; ;;;;;;;;;;;;;;;;; ; Decides whether PHP may expose the fact that it is installed on the server ; (e.g. by adding its signature to the Web server header). It is no security ; threat in any way, but it makes it possible to determine whether you use PHP ; on your server or not. ; http://php.net/expose-php expose_php = On ;;;;;;;;;;;;;;;;;;; ; Resource Limits ; ;;;;;;;;;;;;;;;;;;; ; Maximum execution time of each script, in seconds ; http://php.net/max-execution-time ; Note: This directive is hardcoded to 0 for the CLI SAPI max_execution_time = 30 ; Maximum amount of time each script may spend parsing request data. It's a good ; idea to limit this time on productions servers in order to eliminate unexpectedly ; long running scripts. ; Note: This directive is hardcoded to -1 for the CLI SAPI ; Default Value: -1 (Unlimited) ; Development Value: 60 (60 seconds) ; Production Value: 60 (60 seconds) ; http://php.net/max-input-time max_input_time = 60 ; Maximum input variable nesting level ; http://php.net/max-input-nesting-level ;max_input_nesting_level = 64 ; How many GET/POST/COOKIE input variables may be accepted ; max_input_vars = 1000 ; Maximum amount of memory a script may consume (128MB) ; http://php.net/memory-limit memory_limit = 128M ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ; Error handling and logging ; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ; This directive informs PHP of which errors, warnings and notices you would like ; it to take action for. The recommended way of setting values for this ; directive is through the use of the error level constants and bitwise ; operators. The error level constants are below here for convenience as well as ; some common settings and their meanings. ; By default, PHP is set to take action on all errors, notices and warnings EXCEPT ; those related to E_NOTICE and E_STRICT, which together cover best practices and ; recommended coding standards in PHP. For performance reasons, this is the ; recommend error reporting setting. Your production server shouldn't be wasting ; resources complaining about best practices and coding standards. That's what ; development servers and development settings are for. ; Note: The php.ini-development file has this setting as E_ALL. This ; means it pretty much reports everything which is exactly what you want during ; development and early testing. ; ; Error Level Constants: ; E_ALL - All errors and warnings (includes E_STRICT as of PHP 5.4.0) ; E_ERROR - fatal run-time errors ; E_RECOVERABLE_ERROR - almost fatal run-time errors ; E_WARNING - run-time warnings (non-fatal errors) ; E_PARSE - compile-time parse errors ; E_NOTICE - run-time notices (these are warnings which often result ; from a bug in your code, but it's possible that it was ; intentional (e.g., using an uninitialized variable and ; relying on the fact it's automatically initialized to an ; empty string) ; E_STRICT - run-time notices, enable to have PHP suggest changes ; to your code which will ensure the best interoperability ; and forward compatibility of your code ; E_CORE_ERROR - fatal errors that occur during PHP's initial startup ; E_CORE_WARNING - warnings (non-fatal errors) that occur during PHP's ; initial startup ; E_COMPILE_ERROR - fatal compile-time errors ; E_COMPILE_WARNING - compile-time warnings (non-fatal errors) ; E_USER_ERROR - user-generated error message ; E_USER_WARNING - user-generated warning message ; E_USER_NOTICE - user-generated notice message ; E_DEPRECATED - warn about code that will not work in future versions ; of PHP ; E_USER_DEPRECATED - user-generated deprecation warnings ; ; Common Values: ; E_ALL (Show all errors, warnings and notices including coding standards.) ; E_ALL & ~E_NOTICE (Show all errors, except for notices) ; E_ALL & ~E_NOTICE & ~E_STRICT (Show all errors, except for notices and coding standards warnings.) ; E_COMPILE_ERROR|E_RECOVERABLE_ERROR|E_ERROR|E_CORE_ERROR (Show only errors) ; Default Value: E_ALL & ~E_NOTICE & ~E_STRICT & ~E_DEPRECATED ; Development Value: E_ALL ; Production Value: E_ALL & ~E_DEPRECATED & ~E_STRICT ; http://php.net/error-reporting error_reporting = E_ALL ; This directive controls whether or not and where PHP will output errors, ; notices and warnings too. Error output is very useful during development, but ; it could be very dangerous in production environments. Depending on the code ; which is triggering the error, sensitive information could potentially leak ; out of your application such as database usernames and passwords or worse. ; It's recommended that errors be logged on production servers rather than ; having the errors sent to STDOUT. ; Possible Values: ; Off = Do not display any errors ; stderr = Display errors to STDERR (affects only CGI/CLI binaries!) ; On or stdout = Display errors to STDOUT ; Default Value: On ; Development Value: On ; Production Value: Off ; http://php.net/display-errors display_errors = On ; The display of errors which occur during PHP's startup sequence are handled ; separately from display_errors. PHP's default behavior is to suppress those ; errors from clients. Turning the display of startup errors on can be useful in ; debugging configuration problems. But, it's strongly recommended that you ; leave this setting off on production servers. ; Default Value: Off ; Development Value: On ; Production Value: Off ; http://php.net/display-startup-errors display_startup_errors = On ; Besides displaying errors, PHP can also log errors to locations such as a ; server-specific log, STDERR, or a location specified by the error_log ; directive found below. While errors should not be displayed on productions ; servers they should still be monitored and logging is a great way to do that. ; Default Value: Off ; Development Value: On ; Production Value: On ; http://php.net/log-errors log_errors = On ; Set maximum length of log_errors. In error_log information about the source is ; added. The default is 1024 and 0 allows to not apply any maximum length at all. ; http://php.net/log-errors-max-len log_errors_max_len = 1024 ; Do not log repeated messages. Repeated errors must occur in same file on same ; line unless ignore_repeated_source is set true. ; http://php.net/ignore-repeated-errors ignore_repeated_errors = Off ; Ignore source of message when ignoring repeated messages. When this setting ; is On you will not log errors with repeated messages from different files or ; source lines. ; http://php.net/ignore-repeated-source ignore_repeated_source = Off ; If this parameter is set to Off, then memory leaks will not be shown (on ; stdout or in the log). This has only effect in a debug compile, and if ; error reporting includes E_WARNING in the allowed list ; http://php.net/report-memleaks report_memleaks = On ; This setting is on by default. ;report_zend_debug = 0 ; Store the last error/warning message in $php_errormsg (boolean). Setting this value ; to On can assist in debugging and is appropriate for development servers. It should ; however be disabled on production servers. ; Default Value: Off ; Development Value: On ; Production Value: Off ; http://php.net/track-errors track_errors = On ; Turn off normal error reporting and emit XML-RPC error XML ; http://php.net/xmlrpc-errors ;xmlrpc_errors = 0 ; An XML-RPC faultCode ;xmlrpc_error_number = 0 ; When PHP displays or logs an error, it has the capability of formatting the ; error message as HTML for easier reading. This directive controls whether ; the error message is formatted as HTML or not. ; Note: This directive is hardcoded to Off for the CLI SAPI ; Default Value: On ; Development Value: On ; Production value: On ; http://php.net/html-errors html_errors = On ; If html_errors is set to On *and* docref_root is not empty, then PHP ; produces clickable error messages that direct to a page describing the error ; or function causing the error in detail. ; You can download a copy of the PHP manual from http://php.net/docs ; and change docref_root to the base URL of your local copy including the ; leading '/'. You must also specify the file extension being used including ; the dot. PHP's default behavior is to leave these settings empty, in which ; case no links to documentation are generated. ; Note: Never use this feature for production boxes. ; http://php.net/docref-root ; Examples ;docref_root = "/phpmanual/" ; http://php.net/docref-ext ;docref_ext = .html ; String to output before an error message. PHP's default behavior is to leave ; this setting blank. ; http://php.net/error-prepend-string ; Example: ;error_prepend_string = "" ; String to output after an error message. PHP's default behavior is to leave ; this setting blank. ; http://php.net/error-append-string ; Example: ;error_append_string = "" ; Log errors to specified file. PHP's default behavior is to leave this value ; empty. ; http://php.net/error-log ; Example: ;error_log = php_errors.log ; Log errors to syslog (Event Log on Windows). ;error_log = syslog ;windows.show_crt_warning ; Default value: 0 ; Development value: 0 ; Production value: 0 ;;;;;;;;;;;;;;;;; ; Data Handling ; ;;;;;;;;;;;;;;;;; ; The separator used in PHP generated URLs to separate arguments. ; PHP's default setting is "&". ; http://php.net/arg-separator.output ; Example: ;arg_separator.output = "&" ; List of separator(s) used by PHP to parse input URLs into variables. ; PHP's default setting is "&". ; NOTE: Every character in this directive is considered as separator! ; http://php.net/arg-separator.input ; Example: ;arg_separator.input = ";&" ; This directive determines which super global arrays are registered when PHP ; starts up. G,P,C,E & S are abbreviations for the following respective super ; globals: GET, POST, COOKIE, ENV and SERVER. There is a performance penalty ; paid for the registration of these arrays and because ENV is not as commonly ; used as the others, ENV is not recommended on productions servers. You ; can still get access to the environment variables through getenv() should you ; need to. ; Default Value: "EGPCS" ; Development Value: "GPCS" ; Production Value: "GPCS"; ; http://php.net/variables-order variables_order = "GPCS" ; This directive determines which super global data (G,P,C,E & S) should ; be registered into the super global array REQUEST. If so, it also determines ; the order in which that data is registered. The values for this directive are ; specified in the same manner as the variables_order directive, EXCEPT one. ; Leaving this value empty will cause PHP to use the value set in the ; variables_order directive. It does not mean it will leave the super globals ; array REQUEST empty. ; Default Value: None ; Development Value: "GP" ; Production Value: "GP" ; http://php.net/request-order request_order = "GP" ; This directive determines whether PHP registers $argv & $argc each time it ; runs. $argv contains an array of all the arguments passed to PHP when a script ; is invoked. $argc contains an integer representing the number of arguments ; that were passed when the script was invoked. These arrays are extremely ; useful when running scripts from the command line. When this directive is ; enabled, registering these variables consumes CPU cycles and memory each time ; a script is executed. For performance reasons, this feature should be disabled ; on production servers. ; Note: This directive is hardcoded to On for the CLI SAPI ; Default Value: On ; Development Value: Off ; Production Value: Off ; http://php.net/register-argc-argv register_argc_argv = Off ; When enabled, the ENV, REQUEST and SERVER variables are created when they're ; first used (Just In Time) instead of when the script starts. If these ; variables are not used within a script, having this directive on will result ; in a performance gain. The PHP directive register_argc_argv must be disabled ; for this directive to have any affect. ; http://php.net/auto-globals-jit auto_globals_jit = On ; Whether PHP will read the POST data. ; This option is enabled by default. ; Most likely, you won't want to disable this option globally. It causes $_POST ; and $_FILES to always be empty; the only way you will be able to read the ; POST data will be through the php://input stream wrapper. This can be useful ; to proxy requests or to process the POST data in a memory efficient fashion. ; http://php.net/enable-post-data-reading ;enable_post_data_reading = Off ; Maximum size of POST data that PHP will accept. ; Its value may be 0 to disable the limit. It is ignored if POST data reading ; is disabled through enable_post_data_reading. ; http://php.net/post-max-size post_max_size = 8M ; Automatically add files before PHP document. ; http://php.net/auto-prepend-file auto_prepend_file = ; Automatically add files after PHP document. ; http://php.net/auto-append-file auto_append_file = ; By default, PHP will output a character encoding using ; the Content-type: header. To disable sending of the charset, simply ; set it to be empty. ; ; PHP's built-in default is text/html ; http://php.net/default-mimetype default_mimetype = "text/html" ; PHP's default character set is set to empty. ; http://php.net/default-charset ;default_charset = "UTF-8" ; Always populate the $HTTP_RAW_POST_DATA variable. PHP's default behavior is ; to disable this feature. If post reading is disabled through ; enable_post_data_reading, $HTTP_RAW_POST_DATA is *NOT* populated. ; http://php.net/always-populate-raw-post-data ;always_populate_raw_post_data = On ;;;;;;;;;;;;;;;;;;;;;;;;; ; Paths and Directories ; ;;;;;;;;;;;;;;;;;;;;;;;;; ; UNIX: "/path1:/path2" ;include_path = ".:/php/includes" ; ; Windows: "\path1;\path2" ;include_path = ".;c:\php\includes" ; ; PHP's default setting for include_path is ".;/path/to/php/pear" ; http://php.net/include-path ; The root of the PHP pages, used only if nonempty. ; if PHP was not compiled with FORCE_REDIRECT, you SHOULD set doc_root ; if you are running php as a CGI under any web server (other than IIS) ; see documentation for security issues. The alternate is to use the ; cgi.force_redirect configuration below ; http://php.net/doc-root doc_root = ; The directory under which PHP opens the script using /~username used only ; if nonempty. ; http://php.net/user-dir user_dir = ; Directory in which the loadable extensions (modules) reside. ; http://php.net/extension-dir ; extension_dir = "./" ; On windows: ; extension_dir = "ext" ; Whether or not to enable the dl() function. The dl() function does NOT work ; properly in multithreaded servers, such as IIS or Zeus, and is automatically ; disabled on them. ; http://php.net/enable-dl enable_dl = Off ; cgi.force_redirect is necessary to provide security running PHP as a CGI under ; most web servers. Left undefined, PHP turns this on by default. You can ; turn it off here AT YOUR OWN RISK ; **You CAN safely turn this off for IIS, in fact, you MUST.** ; http://php.net/cgi.force-redirect ;cgi.force_redirect = 1 ; if cgi.nph is enabled it will force cgi to always sent Status: 200 with ; every request. PHP's default behavior is to disable this feature. ;cgi.nph = 1 ; if cgi.force_redirect is turned on, and you are not running under Apache or Netscape ; (iPlanet) web servers, you MAY need to set an environment variable name that PHP ; will look for to know it is OK to continue execution. Setting this variable MAY ; cause security issues, KNOW WHAT YOU ARE DOING FIRST. ; http://php.net/cgi.redirect-status-env ;cgi.redirect_status_env = ; cgi.fix_pathinfo provides *real* PATH_INFO/PATH_TRANSLATED support for CGI. PHP's ; previous behaviour was to set PATH_TRANSLATED to SCRIPT_FILENAME, and to not grok ; what PATH_INFO is. For more information on PATH_INFO, see the cgi specs. Setting ; this to 1 will cause PHP CGI to fix its paths to conform to the spec. A setting ; of zero causes PHP to behave as before. Default is 1. You should fix your scripts ; to use SCRIPT_FILENAME rather than PATH_TRANSLATED. ; http://php.net/cgi.fix-pathinfo ;cgi.fix_pathinfo=1 ; FastCGI under IIS (on WINNT based OS) supports the ability to impersonate ; security tokens of the calling client. This allows IIS to define the ; security context that the request runs under. mod_fastcgi under Apache ; does not currently support this feature (03/17/2002) ; Set to 1 if running under IIS. Default is zero. ; http://php.net/fastcgi.impersonate ;fastcgi.impersonate = 1 ; Disable logging through FastCGI connection. PHP's default behavior is to enable ; this feature. ;fastcgi.logging = 0 ; cgi.rfc2616_headers configuration option tells PHP what type of headers to ; use when sending HTTP response code. If it's set 0 PHP sends Status: header that ; is supported by Apache. When this option is set to 1 PHP will send ; RFC2616 compliant header. ; Default is zero. ; http://php.net/cgi.rfc2616-headers ;cgi.rfc2616_headers = 0 ;;;;;;;;;;;;;;;; ; File Uploads ; ;;;;;;;;;;;;;;;; ; Whether to allow HTTP file uploads. ; http://php.net/file-uploads file_uploads = On ; Temporary directory for HTTP uploaded files (will use system default if not ; specified). ; http://php.net/upload-tmp-dir ;upload_tmp_dir = ; Maximum allowed size for uploaded files. ; http://php.net/upload-max-filesize upload_max_filesize = 2M ; Maximum number of files that can be uploaded via a single request max_file_uploads = 20 ;;;;;;;;;;;;;;;;;; ; Fopen wrappers ; ;;;;;;;;;;;;;;;;;; ; Whether to allow the treatment of URLs (like http:// or ftp://) as files. ; http://php.net/allow-url-fopen allow_url_fopen = On ; Whether to allow include/require to open URLs (like http:// or ftp://) as files. ; http://php.net/allow-url-include allow_url_include = Off ; Define the anonymous ftp password (your email address). PHP's default setting ; for this is empty. ; http://php.net/from ;from="john@doe.com" ; Define the User-Agent string. PHP's default setting for this is empty. ; http://php.net/user-agent ;user_agent="PHP" ; Default timeout for socket based streams (seconds) ; http://php.net/default-socket-timeout default_socket_timeout = 60 ; If your scripts have to deal with files from Macintosh systems, ; or you are running on a Mac and need to deal with files from ; unix or win32 systems, setting this flag will cause PHP to ; automatically detect the EOL character in those files so that ; fgets() and file() will work regardless of the source of the file. ; http://php.net/auto-detect-line-endings ;auto_detect_line_endings = Off ;;;;;;;;;;;;;;;;;;;;;; ; Dynamic Extensions ; ;;;;;;;;;;;;;;;;;;;;;; ; If you wish to have an extension loaded automatically, use the following ; syntax: ; ; extension=modulename.extension ; ; For example, on Windows: ; ; extension=msql.dll ; ; ... or under UNIX: ; ; extension=msql.so ; ; ... or with a path: ; ; extension=/path/to/extension/msql.so ; ; If you only provide the name of the extension, PHP will look for it in its ; default extension directory. ; ; Windows Extensions ; Note that ODBC support is built in, so no dll is needed for it. ; Note that many DLL files are located in the extensions/ (PHP 4) ext/ (PHP 5) ; extension folders as well as the separate PECL DLL download (PHP 5). ; Be sure to appropriately set the extension_dir directive. ; ;extension=php_bz2.dll ;extension=php_curl.dll ;extension=php_fileinfo.dll ;extension=php_gd2.dll ;extension=php_gettext.dll ;extension=php_gmp.dll ;extension=php_intl.dll ;extension=php_imap.dll ;extension=php_interbase.dll ;extension=php_ldap.dll ;extension=php_mbstring.dll ;extension=php_exif.dll ; Must be after mbstring as it depends on it ;extension=php_mysql.dll ;extension=php_mysqli.dll ;extension=php_oci8.dll ; Use with Oracle 10gR2 Instant Client ;extension=php_oci8_11g.dll ; Use with Oracle 11gR2 Instant Client ;extension=php_openssl.dll ;extension=php_pdo_firebird.dll ;extension=php_pdo_mysql.dll ;extension=php_pdo_oci.dll ;extension=php_pdo_odbc.dll ;extension=php_pdo_pgsql.dll ;extension=php_pdo_sqlite.dll ;extension=php_pgsql.dll ;extension=php_pspell.dll ;extension=php_shmop.dll ; The MIBS data available in the PHP distribution must be installed. ; See http://www.php.net/manual/en/snmp.installation.php ;extension=php_snmp.dll ;extension=php_soap.dll ;extension=php_sockets.dll ;extension=php_sqlite3.dll ;extension=php_sybase_ct.dll ;extension=php_tidy.dll ;extension=php_xmlrpc.dll ;extension=php_xsl.dll ;;;;;;;;;;;;;;;;;;; ; Module Settings ; ;;;;;;;;;;;;;;;;;;; [CLI Server] ; Whether the CLI web server uses ANSI color coding in its terminal output. cli_server.color = On [Date] ; Defines the default timezone used by the date functions ; http://php.net/date.timezone ;date.timezone = ; http://php.net/date.default-latitude ;date.default_latitude = 31.7667 ; http://php.net/date.default-longitude ;date.default_longitude = 35.2333 ; http://php.net/date.sunrise-zenith ;date.sunrise_zenith = 90.583333 ; http://php.net/date.sunset-zenith ;date.sunset_zenith = 90.583333 [filter] ; http://php.net/filter.default ;filter.default = unsafe_raw ; http://php.net/filter.default-flags ;filter.default_flags = [iconv] ;iconv.input_encoding = ISO-8859-1 ;iconv.internal_encoding = ISO-8859-1 ;iconv.output_encoding = ISO-8859-1 [intl] ;intl.default_locale = ; This directive allows you to produce PHP errors when some error ; happens within intl functions. The value is the level of the error produced. ; Default is 0, which does not produce any errors. ;intl.error_level = E_WARNING [sqlite] ; http://php.net/sqlite.assoc-case ;sqlite.assoc_case = 0 [sqlite3] ;sqlite3.extension_dir = [Pcre] ;PCRE library backtracking limit. ; http://php.net/pcre.backtrack-limit ;pcre.backtrack_limit=100000 ;PCRE library recursion limit. ;Please note that if you set this value to a high number you may consume all ;the available process stack and eventually crash PHP (due to reaching the ;stack size limit imposed by the Operating System). ; http://php.net/pcre.recursion-limit ;pcre.recursion_limit=100000 [Pdo] ; Whether to pool ODBC connections. Can be one of "strict", "relaxed" or "off" ; http://php.net/pdo-odbc.connection-pooling ;pdo_odbc.connection_pooling=strict ;pdo_odbc.db2_instance_name [Pdo_mysql] ; If mysqlnd is used: Number of cache slots for the internal result set cache ; http://php.net/pdo_mysql.cache_size pdo_mysql.cache_size = 2000 ; Default socket name for local MySQL connects. If empty, uses the built-in ; MySQL defaults. ; http://php.net/pdo_mysql.default-socket pdo_mysql.default_socket= [Phar] ; http://php.net/phar.readonly ;phar.readonly = On ; http://php.net/phar.require-hash ;phar.require_hash = On ;phar.cache_list = [mail function] ; For Win32 only. ; http://php.net/smtp SMTP = localhost ; http://php.net/smtp-port smtp_port = 25 ; For Win32 only. ; http://php.net/sendmail-from ;sendmail_from = me@example.com ; For Unix only. You may supply arguments as well (default: "sendmail -t -i"). ; http://php.net/sendmail-path ;sendmail_path = ; Force the addition of the specified parameters to be passed as extra parameters ; to the sendmail binary. These parameters will always replace the value of ; the 5th parameter to mail(), even in safe mode. ;mail.force_extra_parameters = ; Add X-PHP-Originating-Script: that will include uid of the script followed by the filename mail.add_x_header = On ; The path to a log file that will log all mail() calls. Log entries include ; the full path of the script, line number, To address and headers. ;mail.log = ; Log mail to syslog (Event Log on Windows). ;mail.log = syslog [SQL] ; http://php.net/sql.safe-mode sql.safe_mode = Off [ODBC] ; http://php.net/odbc.default-db ;odbc.default_db = Not yet implemented ; http://php.net/odbc.default-user ;odbc.default_user = Not yet implemented ; http://php.net/odbc.default-pw ;odbc.default_pw = Not yet implemented ; Controls the ODBC cursor model. ; Default: SQL_CURSOR_STATIC (default). ;odbc.default_cursortype ; Allow or prevent persistent links. ; http://php.net/odbc.allow-persistent odbc.allow_persistent = On ; Check that a connection is still valid before reuse. ; http://php.net/odbc.check-persistent odbc.check_persistent = On ; Maximum number of persistent links. -1 means no limit. ; http://php.net/odbc.max-persistent odbc.max_persistent = -1 ; Maximum number of links (persistent + non-persistent). -1 means no limit. ; http://php.net/odbc.max-links odbc.max_links = -1 ; Handling of LONG fields. Returns number of bytes to variables. 0 means ; passthru. ; http://php.net/odbc.defaultlrl odbc.defaultlrl = 4096 ; Handling of binary data. 0 means passthru, 1 return as is, 2 convert to char. ; See the documentation on odbc_binmode and odbc_longreadlen for an explanation ; of odbc.defaultlrl and odbc.defaultbinmode ; http://php.net/odbc.defaultbinmode odbc.defaultbinmode = 1 ;birdstep.max_links = -1 [Interbase] ; Allow or prevent persistent links. ibase.allow_persistent = 1 ; Maximum number of persistent links. -1 means no limit. ibase.max_persistent = -1 ; Maximum number of links (persistent + non-persistent). -1 means no limit. ibase.max_links = -1 ; Default database name for ibase_connect(). ;ibase.default_db = ; Default username for ibase_connect(). ;ibase.default_user = ; Default password for ibase_connect(). ;ibase.default_password = ; Default charset for ibase_connect(). ;ibase.default_charset = ; Default timestamp format. ibase.timestampformat = "%Y-%m-%d %H:%M:%S" ; Default date format. ibase.dateformat = "%Y-%m-%d" ; Default time format. ibase.timeformat = "%H:%M:%S" [MySQL] ; Allow accessing, from PHP's perspective, local files with LOAD DATA statements ; http://php.net/mysql.allow_local_infile mysql.allow_local_infile = On ; Allow or prevent persistent links. ; http://php.net/mysql.allow-persistent mysql.allow_persistent = On ; If mysqlnd is used: Number of cache slots for the internal result set cache ; http://php.net/mysql.cache_size mysql.cache_size = 2000 ; Maximum number of persistent links. -1 means no limit. ; http://php.net/mysql.max-persistent mysql.max_persistent = -1 ; Maximum number of links (persistent + non-persistent). -1 means no limit. ; http://php.net/mysql.max-links mysql.max_links = -1 ; Default port number for mysql_connect(). If unset, mysql_connect() will use ; the $MYSQL_TCP_PORT or the mysql-tcp entry in /etc/services or the ; compile-time value defined MYSQL_PORT (in that order). Win32 will only look ; at MYSQL_PORT. ; http://php.net/mysql.default-port mysql.default_port = ; Default socket name for local MySQL connects. If empty, uses the built-in ; MySQL defaults. ; http://php.net/mysql.default-socket mysql.default_socket = ; Default host for mysql_connect() (doesn't apply in safe mode). ; http://php.net/mysql.default-host mysql.default_host = ; Default user for mysql_connect() (doesn't apply in safe mode). ; http://php.net/mysql.default-user mysql.default_user = ; Default password for mysql_connect() (doesn't apply in safe mode). ; Note that this is generally a *bad* idea to store passwords in this file. ; *Any* user with PHP access can run 'echo get_cfg_var("mysql.default_password") ; and reveal this password! And of course, any users with read access to this ; file will be able to reveal the password as well. ; http://php.net/mysql.default-password mysql.default_password = ; Maximum time (in seconds) for connect timeout. -1 means no limit ; http://php.net/mysql.connect-timeout mysql.connect_timeout = 60 ; Trace mode. When trace_mode is active (=On), warnings for table/index scans and ; SQL-Errors will be displayed. ; http://php.net/mysql.trace-mode mysql.trace_mode = Off [MySQLi] ; Maximum number of persistent links. -1 means no limit. ; http://php.net/mysqli.max-persistent mysqli.max_persistent = -1 ; Allow accessing, from PHP's perspective, local files with LOAD DATA statements ; http://php.net/mysqli.allow_local_infile ;mysqli.allow_local_infile = On ; Allow or prevent persistent links. ; http://php.net/mysqli.allow-persistent mysqli.allow_persistent = On ; Maximum number of links. -1 means no limit. ; http://php.net/mysqli.max-links mysqli.max_links = -1 ; If mysqlnd is used: Number of cache slots for the internal result set cache ; http://php.net/mysqli.cache_size mysqli.cache_size = 2000 ; Default port number for mysqli_connect(). If unset, mysqli_connect() will use ; the $MYSQL_TCP_PORT or the mysql-tcp entry in /etc/services or the ; compile-time value defined MYSQL_PORT (in that order). Win32 will only look ; at MYSQL_PORT. ; http://php.net/mysqli.default-port mysqli.default_port = 3306 ; Default socket name for local MySQL connects. If empty, uses the built-in ; MySQL defaults. ; http://php.net/mysqli.default-socket mysqli.default_socket = ; Default host for mysql_connect() (doesn't apply in safe mode). ; http://php.net/mysqli.default-host mysqli.default_host = ; Default user for mysql_connect() (doesn't apply in safe mode). ; http://php.net/mysqli.default-user mysqli.default_user = ; Default password for mysqli_connect() (doesn't apply in safe mode). ; Note that this is generally a *bad* idea to store passwords in this file. ; *Any* user with PHP access can run 'echo get_cfg_var("mysqli.default_pw") ; and reveal this password! And of course, any users with read access to this ; file will be able to reveal the password as well. ; http://php.net/mysqli.default-pw mysqli.default_pw = ; Allow or prevent reconnect mysqli.reconnect = Off [mysqlnd] ; Enable / Disable collection of general statistics by mysqlnd which can be ; used to tune and monitor MySQL operations. ; http://php.net/mysqlnd.collect_statistics mysqlnd.collect_statistics = On ; Enable / Disable collection of memory usage statistics by mysqlnd which can be ; used to tune and monitor MySQL operations. ; http://php.net/mysqlnd.collect_memory_statistics mysqlnd.collect_memory_statistics = On ; Size of a pre-allocated buffer used when sending commands to MySQL in bytes. ; http://php.net/mysqlnd.net_cmd_buffer_size ;mysqlnd.net_cmd_buffer_size = 2048 ; Size of a pre-allocated buffer used for reading data sent by the server in ; bytes. ; http://php.net/mysqlnd.net_read_buffer_size ;mysqlnd.net_read_buffer_size = 32768 [OCI8] ; Connection: Enables privileged connections using external ; credentials (OCI_SYSOPER, OCI_SYSDBA) ; http://php.net/oci8.privileged-connect ;oci8.privileged_connect = Off ; Connection: The maximum number of persistent OCI8 connections per ; process. Using -1 means no limit. ; http://php.net/oci8.max-persistent ;oci8.max_persistent = -1 ; Connection: The maximum number of seconds a process is allowed to ; maintain an idle persistent connection. Using -1 means idle ; persistent connections will be maintained forever. ; http://php.net/oci8.persistent-timeout ;oci8.persistent_timeout = -1 ; Connection: The number of seconds that must pass before issuing a ; ping during oci_pconnect() to check the connection validity. When ; set to 0, each oci_pconnect() will cause a ping. Using -1 disables ; pings completely. ; http://php.net/oci8.ping-interval ;oci8.ping_interval = 60 ; Connection: Set this to a user chosen connection class to be used ; for all pooled server requests with Oracle 11g Database Resident ; Connection Pooling (DRCP). To use DRCP, this value should be set to ; the same string for all web servers running the same application, ; the database pool must be configured, and the connection string must ; specify to use a pooled server. ;oci8.connection_class = ; High Availability: Using On lets PHP receive Fast Application ; Notification (FAN) events generated when a database node fails. The ; database must also be configured to post FAN events. ;oci8.events = Off ; Tuning: This option enables statement caching, and specifies how ; many statements to cache. Using 0 disables statement caching. ; http://php.net/oci8.statement-cache-size ;oci8.statement_cache_size = 20 ; Tuning: Enables statement prefetching and sets the default number of ; rows that will be fetched automatically after statement execution. ; http://php.net/oci8.default-prefetch ;oci8.default_prefetch = 100 ; Compatibility. Using On means oci_close() will not close ; oci_connect() and oci_new_connect() connections. ; http://php.net/oci8.old-oci-close-semantics ;oci8.old_oci_close_semantics = Off [PostgreSQL] ; Allow or prevent persistent links. ; http://php.net/pgsql.allow-persistent pgsql.allow_persistent = On ; Detect broken persistent links always with pg_pconnect(). ; Auto reset feature requires a little overheads. ; http://php.net/pgsql.auto-reset-persistent pgsql.auto_reset_persistent = Off ; Maximum number of persistent links. -1 means no limit. ; http://php.net/pgsql.max-persistent pgsql.max_persistent = -1 ; Maximum number of links (persistent+non persistent). -1 means no limit. ; http://php.net/pgsql.max-links pgsql.max_links = -1 ; Ignore PostgreSQL backends Notice message or not. ; Notice message logging require a little overheads. ; http://php.net/pgsql.ignore-notice pgsql.ignore_notice = 0 ; Log PostgreSQL backends Notice message or not. ; Unless pgsql.ignore_notice=0, module cannot log notice message. ; http://php.net/pgsql.log-notice pgsql.log_notice = 0 [Sybase-CT] ; Allow or prevent persistent links. ; http://php.net/sybct.allow-persistent sybct.allow_persistent = On ; Maximum number of persistent links. -1 means no limit. ; http://php.net/sybct.max-persistent sybct.max_persistent = -1 ; Maximum number of links (persistent + non-persistent). -1 means no limit. ; http://php.net/sybct.max-links sybct.max_links = -1 ; Minimum server message severity to display. ; http://php.net/sybct.min-server-severity sybct.min_server_severity = 10 ; Minimum client message severity to display. ; http://php.net/sybct.min-client-severity sybct.min_client_severity = 10 ; Set per-context timeout ; http://php.net/sybct.timeout ;sybct.timeout= ;sybct.packet_size ; The maximum time in seconds to wait for a connection attempt to succeed before returning failure. ; Default: one minute ;sybct.login_timeout= ; The name of the host you claim to be connecting from, for display by sp_who. ; Default: none ;sybct.hostname= ; Allows you to define how often deadlocks are to be retried. -1 means "forever". ; Default: 0 ;sybct.deadlock_retry_count= [bcmath] ; Number of decimal digits for all bcmath functions. ; http://php.net/bcmath.scale bcmath.scale = 0 [browscap] ; http://php.net/browscap ;browscap = extra/browscap.ini [Session] ; Handler used to store/retrieve data. ; http://php.net/session.save-handler session.save_handler = files ; Argument passed to save_handler. In the case of files, this is the path ; where data files are stored. Note: Windows users have to change this ; variable in order to use PHP's session functions. ; ; The path can be defined as: ; ; session.save_path = "N;/path" ; ; where N is an integer. Instead of storing all the session files in ; /path, what this will do is use subdirectories N-levels deep, and ; store the session data in those directories. This is useful if you ; or your OS have problems with lots of files in one directory, and is ; a more efficient layout for servers that handle lots of sessions. ; ; NOTE 1: PHP will not create this directory structure automatically. ; You can use the script in the ext/session dir for that purpose. ; NOTE 2: See the section on garbage collection below if you choose to ; use subdirectories for session storage ; ; The file storage module creates files using mode 600 by default. ; You can change that by using ; ; session.save_path = "N;MODE;/path" ; ; where MODE is the octal representation of the mode. Note that this ; does not overwrite the process's umask. ; http://php.net/session.save-path ;session.save_path = "/tmp" ; Whether to use cookies. ; http://php.net/session.use-cookies session.use_cookies = 1 ; http://php.net/session.cookie-secure ;session.cookie_secure = ; This option forces PHP to fetch and use a cookie for storing and maintaining ; the session id. We encourage this operation as it's very helpful in combating ; session hijacking when not specifying and managing your own session id. It is ; not the end all be all of session hijacking defense, but it's a good start. ; http://php.net/session.use-only-cookies session.use_only_cookies = 1 ; Name of the session (used as cookie name). ; http://php.net/session.name session.name = PHPSESSID ; Initialize session on request startup. ; http://php.net/session.auto-start session.auto_start = 0 ; Lifetime in seconds of cookie or, if 0, until browser is restarted. ; http://php.net/session.cookie-lifetime session.cookie_lifetime = 0 ; The path for which the cookie is valid. ; http://php.net/session.cookie-path session.cookie_path = / ; The domain for which the cookie is valid. ; http://php.net/session.cookie-domain session.cookie_domain = ; Whether or not to add the httpOnly flag to the cookie, which makes it inaccessible to browser scripting languages such as JavaScript. ; http://php.net/session.cookie-httponly session.cookie_httponly = ; Handler used to serialize data. php is the standard serializer of PHP. ; http://php.net/session.serialize-handler session.serialize_handler = php ; Defines the probability that the 'garbage collection' process is started ; on every session initialization. The probability is calculated by using ; gc_probability/gc_divisor. Where session.gc_probability is the numerator ; and gc_divisor is the denominator in the equation. Setting this value to 1 ; when the session.gc_divisor value is 100 will give you approximately a 1% chance ; the gc will run on any give request. ; Default Value: 1 ; Development Value: 1 ; Production Value: 1 ; http://php.net/session.gc-probability session.gc_probability = 1 ; Defines the probability that the 'garbage collection' process is started on every ; session initialization. The probability is calculated by using the following equation: ; gc_probability/gc_divisor. Where session.gc_probability is the numerator and ; session.gc_divisor is the denominator in the equation. Setting this value to 1 ; when the session.gc_divisor value is 100 will give you approximately a 1% chance ; the gc will run on any give request. Increasing this value to 1000 will give you ; a 0.1% chance the gc will run on any give request. For high volume production servers, ; this is a more efficient approach. ; Default Value: 100 ; Development Value: 1000 ; Production Value: 1000 ; http://php.net/session.gc-divisor session.gc_divisor = 1000 ; After this number of seconds, stored data will be seen as 'garbage' and ; cleaned up by the garbage collection process. ; http://php.net/session.gc-maxlifetime session.gc_maxlifetime = 1440 ; NOTE: If you are using the subdirectory option for storing session files ; (see session.save_path above), then garbage collection does *not* ; happen automatically. You will need to do your own garbage ; collection through a shell script, cron entry, or some other method. ; For example, the following script would is the equivalent of ; setting session.gc_maxlifetime to 1440 (1440 seconds = 24 minutes): ; find /path/to/sessions -cmin +24 -type f | xargs rm ; Check HTTP Referer to invalidate externally stored URLs containing ids. ; HTTP_REFERER has to contain this substring for the session to be ; considered as valid. ; http://php.net/session.referer-check session.referer_check = ; How many bytes to read from the file. ; http://php.net/session.entropy-length ;session.entropy_length = 32 ; Specified here to create the session id. ; http://php.net/session.entropy-file ; Defaults to /dev/urandom ; On systems that don't have /dev/urandom but do have /dev/arandom, this will default to /dev/arandom ; If neither are found at compile time, the default is no entropy file. ; On windows, setting the entropy_length setting will activate the ; Windows random source (using the CryptoAPI) ;session.entropy_file = /dev/urandom ; Set to {nocache,private,public,} to determine HTTP caching aspects ; or leave this empty to avoid sending anti-caching headers. ; http://php.net/session.cache-limiter session.cache_limiter = nocache ; Document expires after n minutes. ; http://php.net/session.cache-expire session.cache_expire = 180 ; trans sid support is disabled by default. ; Use of trans sid may risk your users security. ; Use this option with caution. ; - User may send URL contains active session ID ; to other person via. email/irc/etc. ; - URL that contains active session ID may be stored ; in publicly accessible computer. ; - User may access your site with the same session ID ; always using URL stored in browser's history or bookmarks. ; http://php.net/session.use-trans-sid session.use_trans_sid = 0 ; Select a hash function for use in generating session ids. ; Possible Values ; 0 (MD5 128 bits) ; 1 (SHA-1 160 bits) ; This option may also be set to the name of any hash function supported by ; the hash extension. A list of available hashes is returned by the hash_algos() ; function. ; http://php.net/session.hash-function session.hash_function = 0 ; Define how many bits are stored in each character when converting ; the binary hash data to something readable. ; Possible values: ; 4 (4 bits: 0-9, a-f) ; 5 (5 bits: 0-9, a-v) ; 6 (6 bits: 0-9, a-z, A-Z, "-", ",") ; Default Value: 4 ; Development Value: 5 ; Production Value: 5 ; http://php.net/session.hash-bits-per-character session.hash_bits_per_character = 5 ; The URL rewriter will look for URLs in a defined set of HTML tags. ; form/fieldset are special; if you include them here, the rewriter will ; add a hidden field with the info which is otherwise appended ; to URLs. If you want XHTML conformity, remove the form entry. ; Note that all valid entries require a "=", even if no value follows. ; Default Value: "a=href,area=href,frame=src,form=,fieldset=" ; Development Value: "a=href,area=href,frame=src,input=src,form=fakeentry" ; Production Value: "a=href,area=href,frame=src,input=src,form=fakeentry" ; http://php.net/url-rewriter.tags url_rewriter.tags = "a=href,area=href,frame=src,input=src,form=fakeentry" ; Enable upload progress tracking in $_SESSION ; Default Value: On ; Development Value: On ; Production Value: On ; http://php.net/session.upload-progress.enabled ;session.upload_progress.enabled = On ; Cleanup the progress information as soon as all POST data has been read ; (i.e. upload completed). ; Default Value: On ; Development Value: On ; Production Value: On ; http://php.net/session.upload-progress.cleanup ;session.upload_progress.cleanup = On ; A prefix used for the upload progress key in $_SESSION ; Default Value: "upload_progress_" ; Development Value: "upload_progress_" ; Production Value: "upload_progress_" ; http://php.net/session.upload-progress.prefix ;session.upload_progress.prefix = "upload_progress_" ; The index name (concatenated with the prefix) in $_SESSION ; containing the upload progress information ; Default Value: "PHP_SESSION_UPLOAD_PROGRESS" ; Development Value: "PHP_SESSION_UPLOAD_PROGRESS" ; Production Value: "PHP_SESSION_UPLOAD_PROGRESS" ; http://php.net/session.upload-progress.name ;session.upload_progress.name = "PHP_SESSION_UPLOAD_PROGRESS" ; How frequently the upload progress should be updated. ; Given either in percentages (per-file), or in bytes ; Default Value: "1%" ; Development Value: "1%" ; Production Value: "1%" ; http://php.net/session.upload-progress.freq ;session.upload_progress.freq = "1%" ; The minimum delay between updates, in seconds ; Default Value: 1 ; Development Value: 1 ; Production Value: 1 ; http://php.net/session.upload-progress.min-freq ;session.upload_progress.min_freq = "1" [MSSQL] ; Allow or prevent persistent links. mssql.allow_persistent = On ; Maximum number of persistent links. -1 means no limit. mssql.max_persistent = -1 ; Maximum number of links (persistent+non persistent). -1 means no limit. mssql.max_links = -1 ; Minimum error severity to display. mssql.min_error_severity = 10 ; Minimum message severity to display. mssql.min_message_severity = 10 ; Compatibility mode with old versions of PHP 3.0. mssql.compatability_mode = Off ; Connect timeout ;mssql.connect_timeout = 5 ; Query timeout ;mssql.timeout = 60 ; Valid range 0 - 2147483647. Default = 4096. ;mssql.textlimit = 4096 ; Valid range 0 - 2147483647. Default = 4096. ;mssql.textsize = 4096 ; Limits the number of records in each batch. 0 = all records in one batch. ;mssql.batchsize = 0 ; Specify how datetime and datetim4 columns are returned ; On => Returns data converted to SQL server settings ; Off => Returns values as YYYY-MM-DD hh:mm:ss ;mssql.datetimeconvert = On ; Use NT authentication when connecting to the server mssql.secure_connection = Off ; Specify max number of processes. -1 = library default ; msdlib defaults to 25 ; FreeTDS defaults to 4096 ;mssql.max_procs = -1 ; Specify client character set. ; If empty or not set the client charset from freetds.conf is used ; This is only used when compiled with FreeTDS ;mssql.charset = "ISO-8859-1" [Assertion] ; Assert(expr); active by default. ; http://php.net/assert.active ;assert.active = On ; Issue a PHP warning for each failed assertion. ; http://php.net/assert.warning ;assert.warning = On ; Don't bail out by default. ; http://php.net/assert.bail ;assert.bail = Off ; User-function to be called if an assertion fails. ; http://php.net/assert.callback ;assert.callback = 0 ; Eval the expression with current error_reporting(). Set to true if you want ; error_reporting(0) around the eval(). ; http://php.net/assert.quiet-eval ;assert.quiet_eval = 0 [COM] ; path to a file containing GUIDs, IIDs or filenames of files with TypeLibs ; http://php.net/com.typelib-file ;com.typelib_file = ; allow Distributed-COM calls ; http://php.net/com.allow-dcom ;com.allow_dcom = true ; autoregister constants of a components typlib on com_load() ; http://php.net/com.autoregister-typelib ;com.autoregister_typelib = true ; register constants casesensitive ; http://php.net/com.autoregister-casesensitive ;com.autoregister_casesensitive = false ; show warnings on duplicate constant registrations ; http://php.net/com.autoregister-verbose ;com.autoregister_verbose = true ; The default character set code-page to use when passing strings to and from COM objects. ; Default: system ANSI code page ;com.code_page= [mbstring] ; language for internal character representation. ; http://php.net/mbstring.language ;mbstring.language = Japanese ; internal/script encoding. ; Some encoding cannot work as internal encoding. ; (e.g. SJIS, BIG5, ISO-2022-*) ; http://php.net/mbstring.internal-encoding ;mbstring.internal_encoding = EUC-JP ; http input encoding. ; http://php.net/mbstring.http-input ;mbstring.http_input = auto ; http output encoding. mb_output_handler must be ; registered as output buffer to function ; http://php.net/mbstring.http-output ;mbstring.http_output = SJIS ; enable automatic encoding translation according to ; mbstring.internal_encoding setting. Input chars are ; converted to internal encoding by setting this to On. ; Note: Do _not_ use automatic encoding translation for ; portable libs/applications. ; http://php.net/mbstring.encoding-translation ;mbstring.encoding_translation = Off ; automatic encoding detection order. ; auto means ; http://php.net/mbstring.detect-order ;mbstring.detect_order = auto ; substitute_character used when character cannot be converted ; one from another ; http://php.net/mbstring.substitute-character ;mbstring.substitute_character = none; ; overload(replace) single byte functions by mbstring functions. ; mail(), ereg(), etc are overloaded by mb_send_mail(), mb_ereg(), ; etc. Possible values are 0,1,2,4 or combination of them. ; For example, 7 for overload everything. ; 0: No overload ; 1: Overload mail() function ; 2: Overload str*() functions ; 4: Overload ereg*() functions ; http://php.net/mbstring.func-overload ;mbstring.func_overload = 0 ; enable strict encoding detection. ;mbstring.strict_detection = Off ; This directive specifies the regex pattern of content types for which mb_output_handler() ; is activated. ; Default: mbstring.http_output_conv_mimetype=^(text/|application/xhtml\+xml) ;mbstring.http_output_conv_mimetype= [gd] ; Tell the jpeg decode to ignore warnings and try to create ; a gd image. The warning will then be displayed as notices ; disabled by default ; http://php.net/gd.jpeg-ignore-warning ;gd.jpeg_ignore_warning = 0 [exif] ; Exif UNICODE user comments are handled as UCS-2BE/UCS-2LE and JIS as JIS. ; With mbstring support this will automatically be converted into the encoding ; given by corresponding encode setting. When empty mbstring.internal_encoding ; is used. For the decode settings you can distinguish between motorola and ; intel byte order. A decode setting cannot be empty. ; http://php.net/exif.encode-unicode ;exif.encode_unicode = ISO-8859-15 ; http://php.net/exif.decode-unicode-motorola ;exif.decode_unicode_motorola = UCS-2BE ; http://php.net/exif.decode-unicode-intel ;exif.decode_unicode_intel = UCS-2LE ; http://php.net/exif.encode-jis ;exif.encode_jis = ; http://php.net/exif.decode-jis-motorola ;exif.decode_jis_motorola = JIS ; http://php.net/exif.decode-jis-intel ;exif.decode_jis_intel = JIS [Tidy] ; The path to a default tidy configuration file to use when using tidy ; http://php.net/tidy.default-config ;tidy.default_config = /usr/local/lib/php/default.tcfg ; Should tidy clean and repair output automatically? ; WARNING: Do not use this option if you are generating non-html content ; such as dynamic images ; http://php.net/tidy.clean-output tidy.clean_output = Off [soap] ; Enables or disables WSDL caching feature. ; http://php.net/soap.wsdl-cache-enabled soap.wsdl_cache_enabled=1 ; Sets the directory name where SOAP extension will put cache files. ; http://php.net/soap.wsdl-cache-dir soap.wsdl_cache_dir="/tmp" ; (time to live) Sets the number of second while cached file will be used ; instead of original one. ; http://php.net/soap.wsdl-cache-ttl soap.wsdl_cache_ttl=86400 ; Sets the size of the cache limit. (Max. number of WSDL files to cache) soap.wsdl_cache_limit = 5 [sysvshm] ; A default size of the shared memory segment ;sysvshm.init_mem = 10000 [ldap] ; Sets the maximum number of open links or -1 for unlimited. ldap.max_links = -1 [mcrypt] ; For more information about mcrypt settings see http://php.net/mcrypt-module-open ; Directory where to load mcrypt algorithms ; Default: Compiled in into libmcrypt (usually /usr/local/lib/libmcrypt) ;mcrypt.algorithms_dir= ; Directory where to load mcrypt modes ; Default: Compiled in into libmcrypt (usually /usr/local/lib/libmcrypt) ;mcrypt.modes_dir= [dba] ;dba.default_handler= [curl] ; A default value for the CURLOPT_CAINFO option. This is required to be an ; absolute path. ;curl.cainfo = ; Local Variables: ; tab-width: 4 ; End:

format指定类型“unsigned int”，但参数的类型为“char*”

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