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, //Num of elements read from filestream
					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 allocation error");}

	conn->db = malloc(sizeof(struct Database));
	if (!conn->db) {
		die("Memmory allocation error");}

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

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

	if (!conn->file) {
		die("Failed to open the file");}

	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, //Num of elems to write
					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++) {
        struct Address addr = {.id = i, .set = 0};
		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("Row already set, delete first");}

	addr->set = 1;
	
	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 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("ID too high");}
	
	switch(action) {
		case 'c':
			Database_create(conn);
			Database_write(conn);
			break;
		case 'g':
			if (argc != 4) {
				die("Action 'get' requires an ID");}

			Database_get(conn,id);
			break; 
		case 's':
			if (argc != 6) {
				die("Action 'set' needs id, name and email");}
			
			Database_set(conn, id, argv[4], argv[5]);
			Database_write(conn);
			break;
		case 'd':
			if (argc != 4) {
				die("Action 'delet' requires an ID");}

			Database_delete(conn,id);
			Database_write(conn);
			break;
		case 'l':
			Database_list(conn);
			break;
		default:
			die("Invalid action specified, options are: c(reate), g(et), s(et), d(elete), l(ist)");}
	Database_close(conn);

	return 0;
}