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

int main(int argc, char *argv[]){
	if (argc != 4){
		fprintf(stderr, "%c <file_name> <32-bit in Hex> <Offset in Hex>", argv[0]);
		exit(1);
	}
	off_t offset;
	ssize_t nb_write;
	int nb, n;
	int fdin;
	fdin = open(argv[1],O_WRONLY);
	if (fdin == -1){
		perror("File can't be opened");
		exit(2);
	}
	offset = (off_t) strtol (argv[3], NULL, 16);
	nb = (int) strtol(argv[2], NULL, 16);
	n = lseek(fdin, offset * sizeof(int), SEEK_SET);
	nb_write=write(fdin, &nb, sizeof(int));
	printf("%x", nb);
	return EXIT_SUCCESS;
}