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

#define NUM_OF_GBYTES 8

/* if verbose is enabled forks are done for printing additional informations */
#define VERBOSE 0

#if VERBOSE
/* forking is not always possible if memory is low */
#define sys(cmd) if(system(cmd) == -1) printf("%s failed\n", cmd);
#else
#define sys(cmd) ;
#endif

#define MEMFREE "free -h"

int main(void)
{
	char *p[NUM_OF_GBYTES];
	int i;

	printf("memory usage:\n");
	sys(MEMFREE);
	printf("\n\n");

	for (i = 0; i < NUM_OF_GBYTES; i++) {
		p[i] = malloc(1024 * 1024 * 1024);
		printf("allocated 1GB: %p\n", p[i]);
		sys(MEMFREE);
	}

	printf("\n\n");

	for (i = 0; i < NUM_OF_GBYTES; i++) {
		if (p[i]) {
			printf("memsetting 1GB: %p\n", p[i]);
			sys("date +%s.%N");
			memset(p[i], 1, 1024 * 1024 * 1024);
			sys("date +%s.%N");
			sys(MEMFREE);
		}
	}

	printf("\n\n");

	for (i = 0; i < NUM_OF_GBYTES; i++) {
		if (p[i]) {
			printf("free 1GB: %p\n", p[i]);
			free(p[i]);
			sys(MEMFREE);
		}
	}
	return 0;
}