Object Encapsulation in ANSI C

class.c

#include <malloc.h>
#include "class.h"
 
/* This is the actual implementation of the class.
 * Because this file isn't included by main.c
 * code in main.c can not access foo except through
 * the functions declared in class.h.
 */
struct my_class_s {
	int foo;
};

void set_foo(my_class *this, int n) {
	this->foo = n;
}

int get_foo(my_class *this) {
	return this->foo;
}

my_class * new_object() {
	return malloc(sizeof(my_class));
}

void free_object(my_class *this) {
	free(this);
}

class.h

/* This is a very simple example class with encapsulation
 * in ANSI C.  It provides encapsulation by only declaring the
 * struct for the class in this header file and defining the "class"
 * only in the source file itself.  This means that source files that
 * include this file don't know about the actual contents of the struct
 * and therefore can not access any members of an object.
 *
 * I wrote this after reading C++ FQA Lite 7.5[1] which hinted at this.
 *
 * [1] http://yosefk.com/c++fqa/class.html#fqa-7.5
 */
#ifndef	MY_CLASS_H
#define MY_CLASS_H

/* Our declaration of the class my_class */
struct my_class_s;
typedef struct my_class_s my_class;

/* This constructor returns a pointer to a new object of the class
 * my_class or it returns NULL if it fails. free_object destroys it.
 */
my_class *new_object();
void free_object(my_class *this);

/* These methods are used for setting and getting the value of the
 * foo member of my_class objects.
 */
void set_foo(my_class *this, int n);
int get_foo(my_class *this);

#endif

main.c

/* This is a simple example of using encapsulation in ANSI C.
 * Check the comments in class.h for more details.
 */
#include <stdio.h>
#include "class.h"

int main() {
	my_class *obj = new_object();
	assert(obj != NULL);
	set_foo(obj, 123);

	printf("%d\n", get_foo(obj));

	free_object(obj);
	return 0;
}