Object-Oriented Programming in C, src: https://embedded2015.hackpad.com/Object-Oriented-Programming-in-C-Xz4AOssZPCj

object.c

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

/* forward declaration */
typedef struct object Object;
typedef int (*func_t)(Object *);

struct object {
        int a, b;
        func_t add, sub;
};
static int add_impl(Object *self) { return self->a + self->b; }
static int sub_impl(Object *self) { return self->a - self->b; }

int init_object(Object **self)
{
        if (NULL == (*self = malloc(sizeof(Object)))) return -1;
        (*self)->a = 0; (*self)->b = 0;
        (*self)->add = add_impl; (*self)->sub = sub_impl;
        return 0;
}

int main(int argc, char *argv[])
{
        Object *o = NULL;
        init_object(&o);
        o->a = 9922; o->b = 5566;
        printf("add = %d, sub = %d\n", o->add(o), o->sub(o));
        return 0;
}

OOP 是一種態度

http://ubuntuforums.org/archive/index.php/t-141536.html

int (*func_t)(int);

creates a variable named func_t that can hold an address of a function that takes one int as an argument and returns an int.

Reference
codeproject: Inheritance and Polymorphism in C
Learn C the hard way: Simple Object System