C ++全局变量声明 [英] C++ Global variable declaration

问题描述

我想要做的只是在头文件中定义一个变量，并在两个不同的cpp文件中使用它，而无需重新定义每次包含该标题的变量

这是我的尝试：

Variables.h

  #ifndef VARIABLES_H //标题卫兵
 #define VARIABLES_H 
 
 static bool bShouldRegister; 
 
 #endif 
  

（我也试过extern但没有改变） p>

在cpp文件中，我给它一个值 :: bShouldRegister = true 或 bShouldRegister = true;

在我的另一个cpp文件中，我通过创建一个线程并检查其值循环检查它的值工作良好）

  while（true）
 {
 if（:: bShouldRegister）//或if （bShouldRegister）
 {
 MessageBox（NULL，Value Changed，Done，MB_OK | MB_ICONINFORMATION）; 
} 
睡眠（100）; 
} 
  

是的，MessageBox从不出现（bShouldRegister永远不会成真： / p>

解决方案

您必须使用 extern ，否则您有<$ c $

将此文件放在头文件（.h）中：

  extern bool bShouldRegister; 
  

一个实现文件（.cpp）：

  bool bShouldRegister; 
  

What I want to do is just to define a variable in a header file and use it on two different cpp files without redefinition that variable each time I include that header
Here is how I tried :

Variables.h

#ifndef VARIABLES_H // header guards
#define VARIABLES_H

static bool bShouldRegister;

#endif

(I also tried extern but nothing changed)

And in a cpp file I give it a value ::bShouldRegister = true or bShouldRegister = true;

In my another cpp file I check it's value by creating a thread and check its value in a loop (and yes my thread function works well)

 while (true)
 {
     if (::bShouldRegister) // Or if (bShouldRegister)
        {
            MessageBox(NULL,"Value Changed","Done",MB_OK|MB_ICONINFORMATION);
        }
  Sleep(100);
 }

And yes, that MessageBox never appears (bShouldRegister never gets true :/)

解决方案

You must use extern, otherwise you have separate bShouldRegister in each translation unit with probably different values.

Put this in a header file (.h):

extern bool bShouldRegister;

 

Put this just in one of implementation files (.cpp):

bool bShouldRegister;

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