Why this header file include create issue?

Question

I have main.c,test.c,test.h and font.h files when i try to print the buffer in font.h in main.c. Its creating compilation timer error. Anything wrong I am done? Please help.

error:

tmp/ccnygNfe.o:(.data+0x0): multiple definition of `c'

/tmp/ccGk8E1o.o:(.data+0x0): first defined here

collect2: error: ld returned 1 exit status

/* Main.c*/


#include <stdio.h>
#include "font.h"
#include "test.h"

int main()
{
    printf("c=%s",c);

    return 0;
}


/*test.c*/

#ifndef _test_
#define _test_

#include "test.h"
#include "font.h"

int add(int a, int b)
{
    return (a+b);
}

#endif

/*test.h*/
extern void add(int a, int b);

/*font.h*/
#ifndef _font_
#define _font_

char c[10]="saji";
extern char c[10];
#endif

not sir. What changes that I want to make for accessing buffer in font.h? — Jonson, Jan 28 '21 at 04:00

KennetsuR · Answer 1 · 2021-01-28T04:39:02.973

2

declare variable in header file, initialize variable in source file.

font.h

extern char c[10];

font.c

char c[10] = "saji\0";

there is some problem in your test.c. function signature is void, but return int.

edited Jan 28 '21 at 04:39

answered Jan 28 '21 at 01:58

KennetsuR

704
8
17

1

Great answer -- but you can futher tidy it up, as you should not need the #ifndef in the header file when it only have the extern decl – Soren Jan 28 '21 at 04:04

score 1 · Answer 2 · answered Jan 28 '21 at 01:51

In your font.h, you are declaring char c twice:

char c[10]="saji";
extern char c[10];

Move extern char c[10]; into main.c / main.h. The declaration should go into the font.h, and the extern should go into the file where you are using the variable referenced with extern.

Why this header file include create issue?

2 Answers2