从另一个文件访问C ++中的extern变量 [英] Access extern variable in C++ from another file

问题描述

我在一个cpp文件中有一个全局变量，在其中给它分配一个值。现在，为了能够在另一个cpp文件中使用它，我将其声明为 extern ，并且此文件具有使用它的多个功能，因此我在全局范围内进行操作。现在可以在一个函数中访问此变量的值，而不能在另一个函数中访问。除了在头文件中使用它以外，其他任何建议都是很好的，因为我浪费了4天时间。

I have a global variable in one of the cpp files, where I am assigning a value to it. Now in order to be able to use it in another cpp file, I am declaring it as extern and this file has multiple functions that use it so I am doing this globally. Now the value of this variable can be accessed in one of the functions and not in the other one. Any suggestions except using it in a header file would be good because I wasted 4 days playing with that.

推荐答案

对不起，我m忽略了对答案的要求，该答案建议使用头文件以外的任何内容。这是标题的用途，当您正确使用它们时...仔细阅读：

Sorry, I'm ignoring the request for answers suggesting anything other than the use of header files. This is what headers are for, when you use them correctly... Read carefully:

global.h

#ifndef MY_GLOBALS_H
#define MY_GLOBALS_H

// This is a declaration of your variable, which tells the linker this value
// is found elsewhere.  Anyone who wishes to use it must include global.h,
// either directly or indirectly.
extern int myglobalint;

#endif

global.cpp

#include "global.h"

// This is the definition of your variable.  It can only happen in one place.
// You must include global.h so that the compiler matches it to the correct
// one, and doesn't implicitly convert it to static.
int myglobalint = 0;

user.cpp

// Anyone who uses the global value must include the appropriate header.
#include "global.h"

void SomeFunction()
{
    // Now you can access the variable.
    int temp = myglobalint;
}

现在，在编译和链接项目时，您必须：

Now, when you compile and link your project, you must:

1. 将每个源（.cpp）文件编译为目标文件；


2. 链接所有目标文件以创建目标文件可执行文件/库/等等。

使用我上面给出的语法，您应该既没有编译错误也没有链接错误。

Using the syntax I have given above, you should have neither compile nor link errors.

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