Creating your own header file in C

foo.h

#ifndef FOO_H_   /* Include guard */#define FOO_H_int foo(int x);  /* An example function declaration */#endif // FOO_H_

foo.c

#include "foo.h"  /* Include the header (not strictly necessary here) */int foo(int x)    /* Function definition */{    return x + 5;}

main.c

#include <stdio.h>#include "foo.h"  /* Include the header here, to obtain the function declaration */int main(void){    int y = foo(3);  /* Use the function here */    printf("%d\n", y);    return 0;}

To compile using GCC

gcc -o my_app main.c foo.c

#ifndef MY_HEADER_H# define MY_HEADER_H//put your function headers here#endif

MY_HEADER_H serves as a double-inclusion guard.

For the function declaration, you only need to define the signature, that is, without parameter names, like this:

int foo(char*);

If you really want to, you can also include the parameter's identifier, but it's not necessary because the identifier would only be used in a function's body (implementation), which in case of a header (parameter signature), it's missing.

This declares the function foo which accepts a char* and returns an int.

In your source file, you would have:

#include "my_header.h"int foo(char* name) {   //do stuff   return 0;}

myfile.h

#ifndef _myfile_h#define _myfile_hvoid function();#endif

myfile.c

#include "myfile.h"void function() {}