C + + multi-file variable resolution _c language

Do not define a variable in the header file, declare the variable in the header file. The definition is placed in the corresponding source file. Other places can only use extern declarations.

For example:

1 declare an int variable in header file A.h:

extern int IX;

2 defining variables in the source file A.cpp

#include "A.h"

int ix=1;

3 declaring multiple file variables in main

#include "A.h"

extern int IX;

It is also possible for you to use IX without declaring it here, as it is already defined in the source file and contains the header file in the source file of main. The declaration simply states that there is already a variable, except that it is in other files and you can use its name.