1. #include <stdio.h>
2. #include <assert.h>
3. #include <stdlib.h>
4. #include <errno.h>
5. #include <string.h>
6. #define MAX_DATA 512
7. #define MAX_ROWS 100
8. struct Address {
9.  int id;
10.  int set;
11.  char name[MAX_DATA];
12.  char email[MAX_DATA];
13. };
14. struct Database {
15.  struct Address rows[MAX_ROWS];
16. };
17. struct Connection {
18.  FILE *file;
19.  struct Database *db;
20. };
21. void die(const char *message)
22. {
23.  if(errno) {
24.  perror(message);
25.  } else {
26.  printf("ERROR: %s\n", message);
27.  }
28.  exit(1);
29. }
30. void Address_print(struct Address *addr)
31. {
32.  printf("%d %s %s\n",
33.  addr->id, addr->name, addr->email);
34. }
35. void Database_load(struct Connection *conn)
36. {
37.  int rc = fread(conn->db, sizeof(struct Database), 1, conn->file);
38.  if(rc != 1) die("Failed to load database.");
39. }
40. struct Connection *Database_open(const char *filename, char mode)
41. {
42.  struct Connection *conn = malloc(sizeof(struct Connection));
43.  if(!conn) die("Memory error");
44.  conn->db = malloc(sizeof(struct Database));
45.  if(!conn->db) die("Memory error");
46.  if(mode == 'c') {
47.  conn->file = fopen(filename, "w");
48.  } else {
49.  conn->file = fopen(filename, "r+");
50.  if(conn->file) {
51.  Database_load(conn);
52.  }
53.  }
54.  if(!conn->file) die("Failed to open the file");
55.  return conn;
56. }
57. void Database_close(struct Connection *conn)
58. {
59.  if(conn) {
60.  if(conn->file) fclose(conn->file);
61.  if(conn->db) free(conn->db);
62.  free(conn);
63.  }
64. }
65. void Database_write(struct Connection *conn)
66. {
67.  rewind(conn->file);
68.  int rc = fwrite(conn->db, sizeof(struct Database), 1, conn->file);
69.  if(rc != 1) die("Failed to write database.");
70.  rc = fflush(conn->file);
71.  if(rc == -1) die("Cannot flush database.");
72. }
73. void Database_create(struct Connection *conn)
74. {
75.  int i = 0;
76.  for(i = 0; i < MAX_ROWS; i++) {
77.  // make a prototype to initialize it
78.  struct Address addr = {.id = i, .set = 0};
79.  // then just assign it
80.  conn->db->rows[i] = addr;
81.  }
82. }
83. void Database_set(struct Connection *conn, int id, const char *name, const cha
84. r *email)
85. {
86.  struct Address *addr = &conn->db->rows[id];
87.  if(addr->set) die("Already set, delete it first");
88.  addr->set = 1;
89.  // WARNING: bug, read the "How To Break It" and fix this
90.  char *res = strncpy(addr->name, name, MAX_DATA);
91.  // demonstrate the strncpy bug
92.  if(!res) die("Name copy failed");
93.  res = strncpy(addr->email, email, MAX_DATA);
94.  if(!res) die("Email copy failed");
95. }
96. void Database_get(struct Connection *conn, int id)
97. {
98.  struct Address *addr = &conn->db->rows[id];
99.  if(addr->set) {
100.  Address_print(addr);
101.  } else {
102.  die("ID is not set");
103.  }
104. }
105. void Database_delete(struct Connection *conn, int id)
106. {
107.  struct Address addr = {.id = id, .set = 0};
108.  conn->db->rows[id] = addr;
109. }
110. void Database_list(struct Connection *conn)
111. {
112.  int i = 0;
113.  struct Database *db = conn->db;
114.  for(i = 0; i < MAX_ROWS; i++) {
115.  struct Address *cur = &db->rows[i];
116.  if(cur->set) {
117.  Address_print(cur);
118.  }
119.  }
120. }
121. int main(int argc, char *argv[])
122. {
123.  if(argc < 3) die("USAGE: ex17 <dbfile> <action> [action params]");
124.  char *filename = argv[1];
125.  char action = argv[2][0];
126.  struct Connection *conn = Database_open(filename, action);
127.  int id = 0;
128.  if(argc > 3) id = atoi(argv[3]);
129.  if(id >= MAX_ROWS) die("There's not that many records.");
130.  switch(action) {
131.  case 'c':
132.  Database_create(conn);
133.  Database_write(conn);
134.  break;
135.  case 'g':
136.  if(argc != 4) die("Need an id to get");
137.  Database_get(conn, id);
138.  break;
139.  case 's':
140.  if(argc != 6) die("Need id, name, email to set");
141.  Database_set(conn, id, argv[4], argv[5]);
142.  Database_write(conn);
143.  break;
144.  case 'd':
145.  if(argc != 4) die("Need id to delete");
146.  Database_delete(conn, id);
147.  Database_write(conn);
148.  break;
149.  case 'l':
150.  Database_list(conn);
151.  break;
152.  default:
153.  die("Invalid action, only: c=create, g=get, s=set, d=del, l=list")
154. ;
155.  }
156.  Database_close(conn);
157.  return 0;
158. }