link error: multiple definition of

link error: multiple definition of

[zhjin]

hi
  this is my code under redhat linux 8.0.

//a.h
#ifndef ah
#define ah
int i;
void add();
#endif 

//a.cpp
#include "a.h"
void add(){
  i++;
}

//c.cpp
#include "a.h"
int main(){
  i = 100;
  add();
  return 0;
}

g++ -c a.cpp     success
g++ c.cpp a.o 
error: a.o(.bss+0x0): multiple definition of 'i'
/tmp/cc0q7tmK.o(.bss+0x0): first defined here
collect2: ld returned 1 exit status.

can someone help me to solve problem? 
thanks.

Re: link error: multiple definition of

[Mike Stump]

On Wednesday, October 16, 2002, at 10:05 PM, zhjin wrote:
> this is my code under redhat linux 8.0.
>
> //a.h
> #ifndef ah
> #define ah
> int i;
> void add();
> #endif
>
> //a.cpp
> #include "a.h"
> void add(){
>   i++;
> }
>
> //c.cpp
> #include "a.h"
> int main(){
>   i = 100;
>   add();
>   return 0;
> }
>
> g++ -c a.cpp     success
> g++ c.cpp a.o
> error: a.o(.bss+0x0): multiple definition of 'i'
> /tmp/cc0q7tmK.o(.bss+0x0): first defined here
> collect2: ld returned 1 exit status.
>
> can someone help me to solve problem?

This is the wrong list for help in programming in C++.  I'd recommend a 
book on C++.  In C++ you are allowed to define some things once.  
Definitions for these things go in .c files.  You can declare them as 
many times as you want.

extern int i;

is a declaration that i will exist, and it is an int.

int i;

is a definition of i.