Обсуждение: troubles with getting data from tables

pgsql-interfaces@
I'm writing a backend for some ftp demon on C.  I want to make it possible 
to authorize server's clients via pgsql. And I have a such problem:

I have a function FCN_VALIDATE_LOGIN which checks if a given users name is ok.

It's looks like this (I've removed some  debug code) :

---cut 8<---

int
FCN_VALIDATE_LOGIN (const char *login)
{       PGresult *res;
       char *query;       query = malloc(256);
       sprintf(query, "SELECT * FROM users WHERE name=\'%s\';", login);
       res = PQexec(conn, query);
       if (!res || PQresultStatus(res) != PGRES_TUPLES_OK) {               fprintf(stderr, "%s\n",
PQresultErrorMessage(conn));              printf("Error\n");       }
 
       if (PQntuples(res) == 1) {               int uid_field_index;               unsigned int *uid;
               uid_field_index = PQfnumber(res, "uid");               uid = (int *) PQgetvalue(res, 0,
uid_field_index);

#ifdef DEBUG       fprintf(stderr, "uid_field_index = %i\n uid %i\n", uid_field_index, uid);
#endif       //      return uid;       } else { // Not such user               return -1;       }
       PQclear(res);
}

---cut 8<---


And I have a such table:

---cut 8<---

CREATE TABLE users (   name character varying NOT NULL,   passwd character varying,   home character varying,   groups
charactervarying NOT NULL,   rights character varying NOT NULL,   uid int4 NOT NULL,   ip_allowed character varying,
max_dl_speedinteger,   bytes_ul_total bigint,   bytes_dl_total bigint,   ratio integer,   flags character varying,
user_slotsinteger,   leech_slots integer
 
);

---cut 8<---

I have only one row in this table where uid is '1001'.

wzdftpd=# select uid from users;
uid
------
1001
(1 row)

But instead of '1001' "uid" value is '134820376'. Where I was wrong?

-Roman Bogorodskiy [Novel]

On Tue, Sep 23, 2003 at 08:17:50PM +0400, Roman Bogorodskiy wrote:
>         sprintf(query, "SELECT * FROM users WHERE name=\'%s\';", login);
>         if (PQntuples(res) == 1) {
>                 int uid_field_index;
>                 unsigned int *uid;
> 
>                 uid_field_index = PQfnumber(res, "uid");

First off, a question: why don't you just select the field you want, so
you know its index in the result set?  That'll probably transport less 
data, save you that PQfnumber() call, and make your code shorter and
more readable.


>                 uid = (int *) PQgetvalue(res, 0, uid_field_index);

> But instead of '1001' "uid" value is '134820376'. Where I was wrong?

The pointer you're getting is a pointer-to-char, i.e. a string.  Unless
you explicitly enabled the "binary tuples" option, what you're getting is
exactly that: a string.  But instead of parsing the string, you're
casting its base pointer to pointer-to-int!


Jeroen

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Jeroen wrote:

> First off, a question: why don't you just select the field you want,
> so you know its index in the result set?  That'll probably transport
> less data, save you that PQfnumber() call, and make your code shorter
> and more readable.

I'm new to libpq programming, so...

> The pointer you're getting is a pointer-to-char, i.e. a string. 
> Unless you explicitly enabled the "binary tuples" option, what you're
> getting is exactly that: a string.  But instead of parsing the string,
> you're casting its base pointer to pointer-to-int!

Thank you fo answer, it realy helped me. 

- -Roman Bogorodskiy [Novel]

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