c++ multiple definitions of a variable

Question

I have 4 files (2 headers, and 2 code files). FileA.cpp, FileA.h, FileB.cpp, FileB.h

FileA.cpp:

#include "FileA.h"  int main() {     hello();     return 0; }  void hello() {     //code here } 

FileA.h:

#ifndef FILEA_H_ #define FILEA_H_ #include "FileB.h" void hello();  #endif /* FILEA_H_ */ 

FileB.cpp:

#include "FileB.h"  void world() {     //more code; } 

FileB.h:

#ifndef FILEB_H_ #define FILEB_H_  int wat; void world();   #endif /* FILEB_H_ */ 

when I try to compile(with eclipse), I get " multiple definition of `wat' " And I don't know why, it seems as it should work just fine.

Answer 1

I'm not going to include all of the details, but you define a global variable, wat twice in your compilation uint.

To fix, use the following:

FileB.h

extern int wat; 

FileB.cpp

int wat = 0; 

This (extern) tells the compile that the variable wat exists somewhere, and that it needs to find it on it's own (in this case, it's in FileB.cpp)