You can use extern keyword for it. If you have already declared some global variable in a .cpp file and want to access the same in another cpp file, better go for extern declarations. In the file where you want to access that variable, add the following statement.

You have declared a global variable in Header.CPP
// Header.CPP
int global_int;

// your code...
Add extern declarations in Other CPP files whereever you want to access.
// Main.CPP
extern int global_int;
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