★关于VC的全局变量/函数？？

[uoyevoli]

在工程中一个Cpp文件中定义的全局变量在另一个Cpp文件中不可见，为什么？

怎么定义整个工程都可见的全局变量/函数？

还有 extern 关键字怎么用？？？

[真糨糊]

例如全局函数为:BOOL IsGlobal()

在其他cpp中若要用这个函数许先申明:extern BOOL IsGlobal();

[csdnzhu]

把变量定义在stdafx.h中，

[uoyevoli]

如果我在定义时用
extren extern BOOL IsGlobal()
{
return FALSE;
}

这代表什么意思？

[真糨糊]

extern
extern declarator // used when variable or function has external linkage

extern string-literal declarator // used when linkage conventions of another
// language are being used for the declarator

extern string-literal { declarator-list } // used when linkage conventions of another
// language are being used for the declarators

The extern keyword declares a variable or function and specifies that it has external linkage (its name is visible from files other than the one in which it's defined). When modifying a variable, extern specifies that the variable has static duration (it is allocated when the program begins and deallocated when the program ends). The variable or function may be defined in another source file, or later in the same file. In C++, when used with a string, extern specifies that the linkage conventions of another language are being used for the declarator(s).

Declarations of variables and functions at file scope are external by default.

In C++, string-literal is the name of a language. The language specifier "C++" is the default. "C" is the only other language specifier currently supported by Microsoft C/C++. This allows you to use functions or variables defined in a C module.

All of the standard include files use the extern "C" syntax to allow the run-time library functions to be used in C++ programs.

For more information, see auto, register, static, const, and volatile.

Example

The following example declares the functions printf, getchar, and putchar with “C” linkage:

// Example of the extern keyword
extern "C" int printf( const char *, ... );

extern "C"
{
int getchar( void );
int putchar( int );
}

[litbox]

对于全局的变量 在一个地方申明 如 ONE.CPP 在另一个地方要用 如 TWO.CPP 那么TWO.CPP中要重新申明一下 关键字就是extern
one.cpp
int temp;
two.cpp
extern int temp;