How to include c header file in another header?

Question

I'm writing ac program using curses library, and want to create some structs reflecting my application UI.

Here's my app.c file

#include <stdlib.h>
#include <stdio.h>
#include "screen.h"

int main() {
    struct screen scr = {
        .win1 = {
            .title = "win1"
        },
        .win2 = {
            .title = "win2"
        }
    };
}

here's screen.h

#ifndef SCREEN_H
#define SCREEN_H

#include "window.h"

struct screen {
    struct window win1;
    struct window win2;

    struct window *focused;
};

#endif

and here's window.h

#ifndef WINDOW_H
#define WINDOW_H

#include "screen.h"

struct window {
    char *title;
    void (*handle_key_event)(struct screen*);
};

#endif

My window struct handle method must receive a reference to screen, to be able to change the focused window in some specific cases. But when I compile this, I get the warning

window.h:8:34: warning: its scope is only this definition or declaration, which is probably not what you want

which is because it doesn't see the screen declaration. How to fix this?

Answer 1

The warning is when the first reference to a struct is inside something else.

Put struct screen; above the declaration of struct window .

Circular dependencies of header files is a bad idea. Consider refactoring. You do not need the definition of a struct to declare pointers to it. The forward declaration will suffice.

Answer 2

This is about fundamental design, nothing else. To have two header files that mutually include each other simply doesn't make any sense, don't do this. #include is to be regarded as a one-way dependency. In program design, more complex objects depend on/consist of less complex ones.

For example a screen contains a window, so it should be the one doing #include "window.h" . While a window doesn't know a thing about screens, it should only concern itself with displaying a window. Cross-communication between the two modules might have to be in a third module.