Question

Could you please solve my problem? looking at the code, it is self explanatory:

a.h:

#include"c.h"
void a()
{
    printf("I am in a\n");
}

c.h:

#include<stdio.h>
void a();
void b();

main.c:

#include"c.h"

main()
{
    a();

}

and gcc main.c will give me:

/tmp/ccuaiUEA.o: In function `main':
main.c:(.text+0x7): undefined reference to `a'
collect2: ld returned 1 exit status

Can you please help me in a way that file extensions (.h and .c) remain unchanged?

Answer 1

You need to rename a.h to c.c and then build and run like this:

$ gcc -Wall main.c c.c -o main
$ ./main

Explanation: your a.h is a source file, not a header, so it need to have a .c suffix, not .h. Its corresponding header is c.h so by convention it should be named c.c. When you build your executable you need to compile and link both main.c and c.c source files, which is why they are both included in the gcc command line.