Segmentation fault (core dumped) [closed] - c

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Closed 9 years ago.
I am new to C, I am learning structure now.
This tries to create an entire small program to manage a database.
#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)
{
addr->set = 1;
char *res = strncpy(addr->name, name, MAX_DATA);
addr->name[MAX_DATA] = '\n';
if(!res) die("Name copy failed");
res = strncpy(addr->email, email, MAX_DATA);
addr->email[MAX_DATA] = '\n';
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;
}
It should be like this:
$ make ex17
cc -Wall -g ex17.c -o ex17
$ ./ex17 db.dat c
$ ./ex17 db.dat s 1 someone someemail
$
$ ./ex17 db.dat l
1 someone someemail
But I get this Error message: Segmentation fault (core dumped).
$ make ex17
cc -Wall -g ex17.c -o ex17
$ ./ex17 db.dat c
$ ./ex17 db.dat s 1 someone someemail
Segmentation fault (core dumped)
I think I've got something wrong in "Database_set". I want to solve this problem but I can not. I want to know what I did wrong. Appreciate any help on this error.

Answer 1

In the line
void Database_set(struct Connection *conn, int id, const char *name, const char *email)
{
addr->set = 1;
Where did you define addr? I don't even understand how this compiles...
Presumably you need to keep a count of the number of valid records in your database, and point addr to the first unused record when you add a new one. This requires an update to your database structure as well as to the functions used for adding and deleting. Or you loop through the database to the first address that is not set. Either way, your function needs to declare addr and set it to something useful before using it as a pointer.
The following lines of code may help (these would be the first lines of the Database_set function):
struct Address *addr;
int ii=0;
while(conn->db->rows[ii].set) ii++;
addr = conn->db->rows + ii;
addr->set = 1;
addr->id = id;
You also need to make the changes shown by craig65535. There are quite possibly other problems with your code, but with these additions I can execute the instructions you gave in your question; it compiles, it runs, it doesn't complain. It's a start.
Oh - and it was able to list the database with the l command...

Answer 2

Assuming addr is of type struct Address *, this is totally wrong:
addr->name[MAX_DATA] = '\n';
addr->name only contains MAX_DATA bytes, so the maximum index you can write to is addr->name[MAX_DATA-1]. Also, you want that string to be null-terminated, so you want:
addr->name[MAX_DATA-2] = '\n';
addr->name[MAX_DATA-1] = '\0';
The same goes for addr->email.