Generic array shuffle and unshuffle

genarrayshuffle.c

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

#define Shuffle(A, B, C) shuffle(A, B, 0, C, sizeof(*A))
#define Unshuffle(A, B, C) unshuffle(A, B, 0, C, sizeof(*A))

typedef struct
{
	int x;
	int y;
} Point;

void * shuffle(void * array, int seed, int index, int len, size_t size);
void * unshuffle(void * array, int seed, int index, int len, size_t size);
void swap(void * num1, void * num2, size_t size);
void printArray(void * array, int len, size_t size, void(*print)(void * item));
void printPoint(void * item);	

int main()
{
	Point array[4] = {{0, 1}, {2, 3}, {4, 5}, {6, 7}}; 
	Shuffle(array, 1, 4);
	printArray(array, 4, sizeof(Point), printPoint);
	puts("\n");
	Unshuffle(array, 1, 4);
	printArray(array, 4, sizeof(Point), printPoint);
	return 0;
}

void * shuffle(void * array, int seed, int index, int len, size_t size)
{
	int result;
	if(index == len)
		return array;
	srand(seed);
	result = rand();
	swap((array + index * size), (array + result%len * size), size);
	return shuffle(array, result, index + 1, len, size);
}

void * unshuffle(void * array, int seed, int index, int len, size_t size)
{
	int result;
	if(index == len)
		return array;
	srand(seed);
	result = rand();
	array = unshuffle(array, result, index + 1, len, size);
	swap((array + index * size), (array + result%len * size), size);
	return array;
}

void swap(void * a, void * b, size_t size)
{
	void * temp = malloc(size);
	memcpy(temp, a, size);
	memcpy(a, b, size);
	memcpy(b, temp, size);
	free(temp);
}

void printArray(void * array, int len, size_t size, void(*print)(void * item))
{
	int i;
	for(i = 0; i < len; i++)
		print((array + i * size));
}

void printPoint(void * item)
{
	Point * pitem = (Point*)item;
	printf("x = %d, y = %d\n", pitem->x, pitem->y);
}