separate compilation in C gives error if function is declared in header file

Question

I have a problem compiling separate module in C with gcc:

basically, i have my header, common.h:

#ifndef COMMON_M
    #include<stdio.h>
    #define COMMON_M
    void print_array(int *a,int n);
    void swap(int *v,int i,int j);
#endif

my functions.c with implementations of functions above:

#include "common.h"
void print_array(int *a,int n) {
    int i=0;
    for(;i<n;++i)
        printf( (i==n-1) ? "%d\n" : "%d ", a[i]);
}
void swap(int *v,int i,int j) {
    int t=v[i];
    v[i]=v[j];
    v[j]=t;
}

and my main:

#include "common.h"
void main() {
    int a[10]={6,2,0,12,4,3,7,-4,12,7};
    print_array(a,10);
    qsort_c(a,0,10);
    print_array(a,10);
}

if i try compiling funcionts.c as a module ( gcc -c functions.c ) i get this error:

error: redefinition of ‘swap’ error: redefinition of ‘print_array’

would anyone kindly help me understand why? I am declaring a function in common.h and defining it in functions.c! I don't see why this shouldn't work in theory.

Thanks in advance,

Are these the exact files you're trying to compile? It works fine for me (I just tried) with GCC 4.2 — Chris, Dec 03 '12 at 15:49
You don't get this error with the source you have shown. There must be something different, either the source or the compile or link step. — Olaf Dietsche, Dec 03 '12 at 15:50
@netcoder somehow I get a feeling he's mixing up compilation and linkage — Vyktor, Dec 03 '12 at 15:58
Try removing the variable names from the function declarations in your header, and also adding `extern` to the declarations. — twalberg, Dec 03 '12 at 16:04

score 0 · Answer 1 · answered Dec 03 '12 at 16:16

0

From the above code, what I am seeing is: You included common.h two times. One in myfunction.c and another in your file, where you have main().

answered Dec 03 '12 at 16:16

cipher

2,414
4
30
54

That should not be a problem, and is, in fact probably for the best as long as `main.c` and `myfunction.c` are compiled separately. That's obviously different if `main.c` `#include`s `myfunction.c`, but that doesn't seem to be the case here (although that would be the reason for the include guards...). – twalberg Dec 03 '12 at 16:50
@twalberg . Since the code worked fine on many of SO user's compiler and mine too, I just guessed if `main.c` `#include`s `myfunction.c` . Then it may have been an cause. If only the user could elaborate – cipher Dec 03 '12 at 16:56

separate compilation in C gives error if function is declared in header file

1 Answers1