Shahriyar Shahriyar - 3 months ago 18
C++ Question

C++ Global variable declaration



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 :/)

Answer

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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