Check if a new memory page is zero filled

check_zero_filled_mmap.c

#include <sys/mman.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>

#define PAGESIZE sysconf(_SC_PAGE_SIZE)

int main() {
	uint8_t* ptr = (uint8_t*) mmap(NULL, PAGESIZE, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
	if (ptr == MAP_FAILED) {
		perror("error while allocating memory page");
		return EXIT_FAILURE;
	}

	unsigned int a = 0;
	for (size_t i=0; i < PAGESIZE; i++) {
		if (ptr[i] != 0) {
			printf("Byte %lu is not null: %x\n", i, ptr[i]);
			a = 1;
		}
	}

	munmap(ptr, PAGESIZE);

	if (a == 0) {
		printf("All bytes are zero!\n");
		return EXIT_SUCCESS;
	} else {
		return EXIT_FAILURE;
	}
}