Question

I need to include file_1.c into main.c. In file_1.c, I currently have multiple functions. If I want to call these functions in main.c, what do I need to do? I have #include”file_1.c” in my main program.

Answer 1

Use standard approach by making header file

#include"file_1.h"

you will have to compile this "file_1.c" together with main.c and make one executable
because function calls are need in run time.

Try this :

create a header file file_1.h

#ifndef _FILE_H
#define _FILE_H

void foo(int );
#endif

give all the declaraion of function and struct definitions (if any) or any global variables

then in file_1.c will contain actual defintion of function

//file_1.c

    #include "file_1.h"
    #include <stdio.h>
    void foo(int x)
    {
      printf("%d\t",x);
    }

//main.c
    #include "file_1.h"

    int main()
    {
    int x=10;
    foo(x);
    return 0;
    }

include header file file_1.h in both (main.c and file_1.c) the c files

In gcc

gcc -Wall main.c file_1.c -o myexe.out