Created
February 12, 2015 15:59
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Simple CRUD in C to understand how one connect to DATABASE
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#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 ("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); | |
// demonstrate the strncpy bug | |
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 is 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 id, name, email to set"); | |
Database_set(conn, id, argv[4], argv[5]); | |
Database_write(conn); | |
break; | |
case 'd': | |
if(argc != 4) die("Need an 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); | |
return 0; | |
} |
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