問題描述

我想要做的只是在頭文件中定義一個變量，并在兩個不同的 cpp 文件中使用它，而無需在每次包含該頭文件時重新定義該變量
這是我嘗試的方法:

變量.h

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

(我也試過 extern 但沒有任何改變)

(I also tried extern but nothing changed)

在一個 cpp 文件中，我給它一個值 ::bShouldRegister = true 或 bShouldRegister = true;

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

在我的另一個 cpp 文件中，我通過創建一個線程并在循環中檢查它的值來檢查它的值(是的，我的線程功能運行良好)

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);
 }

是的，MessageBox 永遠不會出現(bShouldRegister 永遠不會為真:/)

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

推薦答案

必須使用 extern，否則每個翻譯單元中的 bShouldRegister 變量可能不同值.

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

把它放在一個頭文件(.h)中:

Put this in a header file (.h):

extern bool bShouldRegister;

把它放在一個實現文件 (.cpp) 中:

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

bool bShouldRegister;

這篇關于C++ 全局變量聲明的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！