Multi-File Programs

Multi-File Programs

Big programs split source into .c files and declarations into headers (.h).

Header file: mymath.h

#ifndef MYMATH_H
#define MYMATH_H
int square(int x);
#endif

Main program

#include "mymath.h"

int main() {
    printf("%d", square(5));
    return 0;
}

Separate .c for the implementation

int square(int x) { return x * x; }

Compile together

gcc main.c mymath.c -o app

Include guard

#ifndef MYMATH_H ... #endif prevents double inclusion.

TL;DR

• Headers hold declarations.
• .c files hold definitions.
• Include guards stop duplication.
• List all .c files when compiling.