Playing with binary IO

lcthw/.ex17play.argv

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

lcthw/ex17play.c

@@ -0,0 +1,109 @@
+#include <err.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+
+#define NAME_SIZE 64
+
+struct State {
+	int counter;
+	time_t updated_at;
+	char name[NAME_SIZE];
+	size_t history_entries;
+};
+
+static char *names[] = {
+	"boingo",
+	"barko",
+	"flip",
+	"dingles",
+	"zebra",
+	"horus",
+	"blendy",
+	"kitems",
+	"horple",
+	NULL,
+};
+
+char *random_name()
+{
+	int i = 0;
+	int mod = 0;
+	for (i = 0; names[i] != NULL; i++) {
+		mod = i;
+	}
+
+	return names[random() % mod];
+}
+
+void tick(FILE *fp, int init)
+{
+	struct State *state = malloc(sizeof(struct State));
+	if (!state) {
+		err(EXIT_FAILURE, "Memory error making State");
+	}
+
+	if (init == 0) {
+		size_t read = fread(state, sizeof(struct State), 1, fp);
+
+		fprintf(
+			stderr,
+			"Read %d \"%s\" (%lu byte(s)) from %lu\n",
+			state->counter, state->name, sizeof(struct State) * read, state->updated_at
+		);
+	}
+
+	time_t history[state->history_entries];
+	size_t histories_read = fread(&history, sizeof(time_t), state->history_entries, fp);
+
+	state->counter++;
+	state->updated_at = time(0);
+	strncpy(state->name, random_name(), NAME_SIZE);
+	state->history_entries++;
+
+	rewind(fp);
+
+	size_t wrote = fwrite(state, sizeof(struct State), 1, fp);
+	fwrite(history, sizeof(time_t), sizeof(history) / sizeof(time_t), fp);
+	fwrite(&state->updated_at, sizeof(time_t), 1, fp);
+
+	fprintf(
+		stderr,
+		"Wrote %d \"%s\" (%lu byte(s)) at %lu (history length=%lu)\n",
+		state->counter, state->name, sizeof(struct State) * wrote, state->updated_at,
+		state->history_entries
+	);
+}
+
+int main(int argc, char *argv[])
+{
+	if (argc < 2) {
+		errx(EXIT_FAILURE, "Missing filename argument");
+	}
+
+	int random_seed = time(0);
+	const char *random_seed_str = getenv("RANDOM_SEED");
+	if (random_seed_str) {
+		random_seed = atoi(random_seed_str);
+	}
+
+	srandom(random_seed);
+
+	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");
+	}
+
+	tick(fp, init);
+	fclose(fp);
+
+	return 0;
+}