Simple example demonstrating function pointers and how different functions could be assigned to instances of the same struct

dynamic_function_assignment.c

#include <stdio.h>

/**
 * Example demonstrating function pointers in a struct that can be
 * assigned on a per-type basis (inspired by Quake 3 source's g_local.h's gentity_s type)
 */
 
typedef struct gscreen_s gscreen_t;
typedef struct ggame_s ggame_t;
 
struct ggame_s {
	int 	width;
 	int 	height;
};
 
struct gscreen_s {
 	int id; // A normal struct property
 	
 	void (*draw)(gscreen_t* theScreen, float delta); 	// A function pointer that can be assigned and called,
 			     										// where draw is the name, int is the return type, and delta is a param.
};

void ScreenDraw_Main(gscreen_t* theScreen, float delta) {
	printf("Drawing #%d with delta %f\n", theScreen->id, delta);
}

int main(void) {
	// Typical struct usage
	gscreen_t mainScreen;
	mainScreen.id = 10;
	mainScreen.draw = ScreenDraw_Main;
	
	printf("Main Screen ID: %d\n", mainScreen.id);
	mainScreen.draw(&mainScreen, 1.25f);
	
	return 0;
}