Global Variable within Multiple Files

Question

I have two source files that need to access a common variable. What is the best way to do this? e.g.:

source1.cpp:

int global;  int function();  int main() {     global=42;     function();     return 0; } 

source2.cpp:

int function() {     if(global==42)         return 42;     return 0; } 

Should the declaration of the variable global be static, extern, or should it be in a header file included by both files, etc?

Answer 1

The global variable should be declared extern in a header file included by both source files, and then defined in only one of those source files:

common.h

extern int global; 

source1.cpp

#include "common.h"  int global;  int function();   int main() {     global=42;     function();     return 0; } 

source2.cpp

#include "common.h"  int function() {     if(global==42)         return 42;     return 0; }