first working version of ex17.c

ex17.c

@@ -0,0 +1,198 @@
+#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);
+        }
+    }
+
+    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, 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'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 id, name, 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);
+
+    return 0;
+}