一个类型指针去减1，这是什么语法???

liuzu2016 2012-07-01 01:09:20

CMapPtrToPtr源码中的

struct __POSITION
{
};

typedef __POSITION* POSITION;

#define BEFORE_START_POSITION ((POSITION)-1L) //看到没有，一个类型指针去减1，这是什么语法???

_AFXCOLL_INLINE POSITION CMapPtrToPtr::GetStartPosition() const
{ return (m_nCount == 0) ? NULL : BEFORE_START_POSITION; } //BEFORE_START_POSITION; 看到这个宏了吧

是否是我查看源码错了，。还是什么原因??

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liuzu2016 2012-07-01

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明白了，就是定义值，作为参考

类似NULL

c中的(void*)0

[Quote=引用 4 楼的回复:]
C/C++ code
(int*)-1
[/Quote]

yulinlang 2012-07-01

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(int*)-1

liuzu2016 2012-07-01

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类比一下啊

int* -1

这种语法对吗？？

[Quote=引用 2 楼的回复:]
这个是强制类型转换，把-1转换为__POSITION*
[/Quote]

yulinlang 2012-07-01

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这个是强制类型转换，把-1转换为__POSITION*

liuzu2016 2012-07-01

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The C programming Language 第二版英文版內容列表 Table of Contents Preface.......................................................... Preface to the first edition..................................... Introduction..................................................... Chapter 1 - A Tutorial Introduction.............................. 1.1 Getting Started................................ 1.2 Variables and Arithmetic Expressions........... 1.3 The for statement.............................. 1.4 Symbolic Constants............................. 1.5 Character Input and Output..................... 1.5.1 File Copying.......................... 1.5.2 Character Counting.................... 1.5.3 Line Counting......................... 1.5.4 Word Counting......................... 1.6 Arrays......................................... 1.7 Functions...................................... 1.8 Arguments - Call by Value...................... 1.9 Character Arrays............................... 1.10 External Variables and Scope.................. Chapter 2 - Types, Operators and Expressions..................... 2.1 Variable Names................................. 2.2 Data Types and Sizes........................... 2.3 Constants...................................... 2.4 Declarations................................... 2.5 Arithmetic Operators........................... 2.6 Relational and Logical Operators............... 2.7 Type Conversions............................... 2.8 Increment and Decrement Operators.............. 2.9 Bitwise Operators.............................. 2.10 Assignment Operators and Expressions.......... 2.11 Conditional Expressions....................... 2.12 Precedence and Order of Evaluation............ Chapter 3 - Control Flow......................................... 3.1 Statements and Blocks.......................... 3.2 If-Else........................................ 3.3 Else-If........................................ 3.4 Switch......................................... 3.5 Loops - While and For.......................... 3.6 Loops - Do-While............................... 3.7 Break and Continue............................. 3.8 Goto and labels................................ Chapter 4 - Functions and Program Structure...................... 4.1 Basics of Functions............................ 4.2 Functions Returning Non-integers............... 4.3 External Variables............................. 4.4 Scope Rules.................................... 4.5 Header Files................................... 4.6 Static Variables................................ 4.7 Register Variables.............................. 4.8 Block Structure................................. 4.9 Initialization.................................. 4.10 Recursion...................................... 4.11 The C Preprocessor............................. 4.11.1 File Inclusion........................ 4.11.2 Macro Substitution.................... 4.11.3 Conditional Inclusion................. Chapter 5 - Pointers and Arrays.................................. 5.1 Pointers and Addresses......................... 5.2 Pointers and Function Arguments................ 5.3 Pointers and Arrays............................ 5.4 Address Arithmetic............................. 5.5 Character Pointers and Functions............... 5.6 Pointer Arrays; Pointers to Pointers........... 5.7 Multi-dimensional Arrays....................... 5.8 Initialization of Pointer Arrays............... 5.9 Pointers vs. Multi-dimensional Arrays.......... 5.10 Command-line Arguments........................ 5.11 Pointers to Functions......................... 5.12 Complicated Declarations...................... Chapter 6 - Structures........................................... 6.1 Basics of Structures........................... 6.2 Structures and Functions....................... 6.3 Arrays of Structures........................... 6.4 Pointers to Structures......................... 6.5 Self-referential Structures.................... 6.6 Table Lookup................................... 6.7 Typedef........................................ 6.8 Unions......................................... 6.9 Bit-fields..................................... Chapter 7 - Input and Output..................................... 7.1 Standard Input and Output....................... 7.2 Formatted Output - printf....................... 7.3 Variable-length Argument Lists.................. 7.4 Formatted Input - Scanf......................... 7.5 File Access..................................... 7.6 Error Handling - Stderr and Exit................ 7.7 Line Input and Output........................... 7.8 Miscellaneous Functions......................... 7.8.1 String Operations...................... 7.8.2 Character Class Testing and Conversion. 7.8.3 Ungetc................................. 7.8.4 Command Execution...................... 7.8.5 Storage Management..................... 7.8.6 Mathematical Functions................. 7.8.7 Random Number generation............... Chapter 8 - The UNIX System Interface............................ 8.1 File Descriptors............................... 8.2 Low Level I/O - Read and Write................. 8.3 Open, Creat, Close, Unlink..................... 8.4 Random Access - Lseek.......................... 8.5 Example - An implementation of Fopen and Getc.. 8.6 Example - Listing Directories.................. 8.7 Example - A Storage Allocator.................. Appendix A - Reference Manual.................................... A.1 Introduction................................... A.2 Lexical Conventions............................ A.2.1 Tokens................................ A.2.2 Comments.............................. A.2.3 Identifiers........................... A.2.4 Keywords.............................. A.2.5 Constants............................. A.2.6 String Literals....................... A.3 Syntax Notation................................ A.4 Meaning of Identifiers......................... A.4.1 Storage Class......................... A.4.2 Basic Types........................... A.4.3 Derived types......................... A.4.4 Type Qualifiers....................... A.5 Objects and Lvalues............................ A.6 Conversions.................................... A.6.1 Integral Promotion.................... A.6.2 Integral Conversions.................. A.6.3 Integer and Floating.................. A.6.4 Floating Types........................ A.6.5 Arithmetic Conversions................ A.6.6 Pointers and Integers................. A.6.7 Void.................................. A.6.8 Pointers to Void...................... A.7 Expressions.................................... A.7.1 Pointer Conversion.................... A.7.2 Primary Expressions................... A.7.3 Postfix Expressions................... A.7.4 Unary Operators....................... A.7.5 Casts................................. A.7.6 Multiplicative Operators.............. A.7.7 Additive Operators.................... A.7.8 Shift Operators....................... A.7.9 Relational Operators.................. A.7.10 Equality Operators................... A.7.11 Bitwise AND Operator................. A.7.12 Bitwise Exclusive OR Operator........ A.7.13 Bitwise Inclusive OR Operator........ A.7.14 Logical AND Operator................. A.7.15 Logical OR Operator.................. A.7.16 Conditional Operator................. A.7.17 Assignment Expressions............... A.7.18 Comma Operator.......................... A.7.19 Constant Expressions.................... A.8 Declarations..................................... A.8.1 Storage Class Specifiers................. A.8.2 Type Specifiers.......................... A.8.3 Structure and Union Declarations......... A.8.4 Enumerations............................. A.8.5 Declarators.............................. A.8.6 Meaning of Declarators................... A.8.7 Initialization........................... A.8.8 Type names............................... A.8.9 Typedef.................................. A.8.10 Type Equivalence........................ A.9 Statements....................................... A.9.1 Labeled Statements....................... A.9.2 Expression Statement..................... A.9.3 Compound Statement....................... A.9.4 Selection Statements..................... A.9.5 Iteration Statements..................... A.9.6 Jump statements.......................... A.10 External Declarations........................... A.10.1 Function Definitions.................... A.10.2 External Declarations................... A.11 Scope and Linkage............................... A.11.1 Lexical Scope........................... A.11.2 Linkage................................. A.12 Preprocessing................................... A.12.1 Trigraph Sequences...................... A.12.2 Line Splicing........................... A.12.3 Macro Definition and Expansion.......... A.12.4 File Inclusion.......................... A.12.5 Conditional Compilation................. A.12.6 Line Control............................ A.12.7 Error Generation........................ A.12.8 Pragmas................................. A.12.9 Null directive.......................... A.12.10 Predefined names....................... A.13 Grammar......................................... Appendix B - Standard Library.................................... B.1.1 File Operations................................ B.1.2 Formatted Output......................... B.1.3 Formatted Input.......................... B.1.4 Character Input and Output Functions..... B.1.5 Direct Input and Output Functions........ B.1.6 File Positioning Functions............... B.1.7 Error Functions.......................... B.2 Character Class Tests: ................. B.3 String Functions: ..................... B.4 Mathematical Functions: ................. B.5 Utility Functions: ....................

●指针也是一种数据类型，指针变量也是一种变量●指针变量指向谁，就把谁的地址赋值给指针变量●类型变量;类型 * 指针变量 = &变量;& 叫取地址，返回操作数的内存地址叫解引用，指操作指针所指向的变量的值在定义变量时，* 号表示所声明的变量为指针类型指针变量要保存某个变量的地址，指针变量的类型比这个变量的类型多一个*在指针使用时，* 号表示操作指针所指向的内存空间示例代码：// 定义一个int类型的变量，同时赋值为10int a = 10;

目录到底什么是指针呢？指针指针地址和指针类型指针取值指针变量初始化指针运算符多重指针指针运算到底什么是指针呢？内存就是一系列有序列号的存储单元，变量就是编译器为内存地址分配的昵称，那么指针是什么呢？指针就是一个指向另一个内存地址变量的值指针指向变量的内存地址，指针就像该变量值的内存地址一样我们来看一个代码片段 func main() { ...

title: C语言[指针] date: 2020-03-31 12:40:36 author: JF blog: https://www.huqifa.com/ summary: 为什么会有指针？这门技术解决了什么问题？ tags: - C语言 - 指针 categories: - C语言 C语言指针学习 1. 为什么会有指针？这门技术解决了什么问题？转载：https://blog.csd...

指针也一样，定义了不赋初值，其保存的地址就会是随机地址，即指向内存中随机的数据，这很危险，说不定指向的是系统运行所必须的一个很重要的数据，如果通过指针修改指向的数据，可能系统就崩溃了（虽然并不会这样，系统的文件一般会有保护的，没那么容易修改），所以为了避免悲剧，指针必须赋初值。地址不能被保存到普通变量中，这时候就到指针变量出场了，指针变量这种变量是专门用来保存地址的，指针变量也可简称为指针。a、b 本身的值没变，变的只是指针 p、q 指向的数据，p 指针指向最大的数，q 指向最小的数。

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