c - Proper use of header files

Question

Coming up with errors for undefined references in main.c. This is because I have several files in this fashion:

main.c
{
    #include "somefile.h"
    somfunct() <--- undefined reference error
}

somefile.h
{
    somefunct() declaration
    ...
}

somefile.c
{
    #include "somefile.h"
    somefunct() definition
    ...
}

I am trying to use proper organization in that I use only declarations in the header files and define them in a separate file. After splitting up my code I get the undefined reference error because there is no link between somefile.h and somefile.c. Even though main.c includes the somefile.h header file, there is nothing in somefile.h that explicitly mentions somefile.c, so my functions are only partially defined. What is the proper way to take care of this problem? Many thanks. I hope this is clear let me know if not.

Answer 1

Here's a complete and working example of your goal.

main.c

#include "somefile.h"

int main() {
    somefunc();
    return 0;
}

somefile.h

#ifndef RHURAC_SOMEFILE_H
#define RHURAC_SOMEFILE_H

void somefunc();

#endif

somefile.c

#include <stdio.h>
#include "somefile.h"

void somefunc() {
    printf("hello
");
}

---

example build ( gcc )

gcc main.c somefile.c -o main

output

$ ./main 
hello