Playing with binary read/write

lcthw/.ex17play.argv

@@ -0,0 +1 @@
+ex17play.bin

lcthw/ex17play.c

@@ -0,0 +1,38 @@
+#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;
+}