ex17.c

#include <stdio.h>
#include <assert.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>

#define MAX_DATA 512
#define MAX_ROWS 100

struct Address{
	int id;
	int set;
	char name[MAX_DATA];
	char email[MAX_DATA];
};

struct Database{
	struct Address rows[MAX_ROWS];
};

struct Connection{
	FILE *file;
	struct Database *db;
};

void die(const char *message)
{
	if(errno){
		perror(message);
	} else {
		printf("ERROR: %s\n", message);
	}

	exit(1);
}

void Address_print(struct Address *addr)
{
	printf("%d %s %s\n",
			addr->id, addr->name, addr->email);
}

void Database_load(struct Connection *conn)
{
	int rc = fread(conn->db, sizeof(struct Database), 1, conn->file);
	if(rc != 1) die("Failed to load database");
}

struct Connection* Database_open(const char *filename, char mode)
{
	struct Connection *conn = malloc(sizeof(struct Connection));
	if(!conn) die("Memory error");

	conn->db = malloc(sizeof(struct Database));
	if(!conn->db) die("Memory error");

	if(mode == 'c'){
		conn->file = fopen(filename, "w");
	} else {
		conn->file = fopen(filename, "r+");

		if(conn->file){
			Database_load(conn);
		}
	}

	return conn;
}

void Database_close(struct Connection *conn)
{
	if(conn){	
		if(conn->file) fclose(conn->file);
		if(conn->db) free(conn->db);
		free(conn);
	}
}

void Database_write(struct Connection *conn){
	rewind(conn->file);

	int rc = fwrite(conn->db, sizeof(struct Database), 1, conn->file);
	if(rc != 1) die("Failed to write database.");

	rc = fflush(conn->file);
	if(rc == -1) die("Cannot flush database.");
}

void Database_create(struct Connection *conn){
	int i = 0;

	for(i = 0 ; i < MAX_ROWS ; i++){
		// make a prototype to initialize it
		struct Address addr = {.id = i , .set = 0};
		// then just assign it
		conn->db->rows[i] = addr;
	}
}

void Database_set(struct Connection *conn, 
		          int id, 
				  const char *name,
				  const char *email)
{
	struct Address *addr = &conn->db->rows[id];
	if(addr->set) die("Address already set, delete it first");

	addr->set = 1;
	// Warning: bug, read the "How to break it" and fix this
	char *res = strncpy(addr->name, name, MAX_DATA);
	if(!res) die("Name copy failed.");

	res = strncpy(addr->email, email, MAX_DATA);
	if(!res) die("Email copy failed.");
}

void Database_get(struct Connection *conn, int id)
{
	struct Address *addr = &conn->db->rows[id];
	if(addr->set){
		Address_print(addr);
	} else {
		die("ID is not set.");
	}
}

void Database_delete(struct Connection *conn, int id)
{
	struct Address addr = {.id = id, .set = 0};
	conn->db->rows[id] = addr;
}

void Database_list(struct Connection *conn)
{
	int i = 0;
	struct Database *db = conn->db;

	for(i = 0 ; i < MAX_ROWS ; i++){
		struct Address *cur = &db->rows[i];

		if(cur->set){
			Address_print(cur);
		}
	}
}

int main(int argc, char *argv[])
{
	if(argc < 3) die("USAGE: ex17 <dbfile> <action> [action params]");

	char *filename = argv[1];
	char action = argv[2][0];
	struct Connection *conn = Database_open(filename, action);
	int id = 0;

	if(argc > 3) id = atoi(argv[3]);
	if(id >= MAX_ROWS) die("There's not that many records.");

	switch(action){
		case 'c':
			Database_create(conn);
			Database_write(conn);
			break;

		case 'g':
			if(argc != 4) die("Need an id to get");
			Database_get(conn, id);
			break;

		case 's':
			if(argc != 6) die("Need an id, name and email to set");
			Database_set(conn, id, argv[4], argv[5]);
			Database_write(conn);
			break;

		case 'd':
			if(argc != 4) die("Need id to delete");

			Database_delete(conn, id);
			Database_write(conn);
			break;

		case 'l':
			Database_list(conn);
			break;

		default:
			die("Invalid action, only: c=create g=get s=set d=del l=list");
	}

	Database_close(conn);
}