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

int main(int argc, char *argv[])
{
	if (argc < 2) {
		errx(EXIT_FAILURE, "Missing filename argument\n");
	}

	int init = 0;
	FILE *fp = fopen(argv[1], "r+");

	if (!fp) {
		fp = fopen(argv[1], "w+");
		init = 1;
	}

	if (!fp) {
		err(EXIT_FAILURE, "Failed to open file\n");
	}

	int counter = 0;
	if (!init) {
		fread(&counter, sizeof(int), 1, fp);
	}

	counter++;

	rewind(fp);

	size_t wrote = fwrite(&counter, sizeof(int), 1, fp);
	fprintf(stderr, "Wrote %d (%lu bytes)\n", counter, wrote);

	fclose(fp);

	return 0;
}