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Re: Help with returning data type

From: Janet Borschowa <borschow(at)roguewave(dot)com>
To: 'Rudinei Dias' <rudinei(at)unilasalle(dot)edu(dot)br>,pgsql-interfaces(at)postgresql(dot)org
Subject: Re: Help with returning data type
Date: 2005-02-17 00:50:26
Message-ID: D486606E7AD20947BDB7E56862E04C39BDC964@cvo1.cvo.roguewave.com (view raw or flat)
Thread:
Lists: pgsql-interfaces
Hi,
This isn't working because the char* you are getting back from PQgetvalue is
either 't' or 'f' and so atol() fails. Also, you should not being calling
PQclear on the PGresult until you are done with it and all the data it
returned via PQgetvalue:

        i = 0;
        bytea = PQgetvalue(res, i, 0);
        //PQclear(res); // don't call this here because you are using bytea
in the next call!
        strcpy(string, bytea);
        PQclear(res); // call it here!
        *var_len = strlen(string);
        return (unsigned char *) string;

One other point, the table's schema should not use the datatype "name" as
this is datatype is only for storage of internal catalog names. It would be
much better to use "varchar(64)".

========================
Janet Borschowa
Software Engineer, Database Products                       
Rogue Wave Software, a QUOVADX(tm) Division
(541) 753-1931   FAX: (541) 757-4630
mailto:borschow(at)roguewave(dot)com  http://www.roguewave.com 




-----Original Message-----
From: Rudinei Dias [mailto:rudinei(at)unilasalle(dot)edu(dot)br] 
Sent: Wednesday, February 16, 2005 5:07 AM
To: pgsql-interfaces(at)postgresql(dot)org
Subject: [INTERFACES] Help with returning data type


Help with returning data type

Hi.

I'm in trouble with data type returns using libpq (PQgetvalue)

see table definition
-  datname name NOT NULL,
-  encoding int4 NOT NULL,
-  datistemplate bool NOT NULL,
-  datallowconn bool NOT NULL,

I codify with this way in C

  static long long_ret;
  static u_long ulong_ret;
  static unsigned char string[SPRINT_MAX_LEN];
  static oid objid[MAX_OID_LEN];
  static struct counter64 c64;
  int i, index;
  char* bytea;

*       // 1 - THIS WORKS (retrieving varchar)
*
        strcpy(query_string, "SELECT datname FROM pg_database limit 1 
offset 0");
        res = PQexec(conn, query_string);                 
        if (PQresultStatus(res) != PGRES_TUPLES_OK){
            fprintf(stderr, "SELECT query failed [%s].\n", query_string);
            PQclear(res);
            return;
        }
        i = 0;
        bytea = PQgetvalue(res, i, 0);
        PQclear(res);
        strcpy(string, bytea);
        *var_len = strlen(string);
        return (unsigned char *) string;

*       // 2 - THIS WORKS (retrieving int4)
*
        strcpy(query_string, "SELECT encoding FROM pg_database limit 1 
offset 0");
        res = PQexec(conn, query_string);                 
        if (PQresultStatus(res) != PGRES_TUPLES_OK){
            fprintf(stderr, "SELECT query failed [%s].\n", query_string);
            PQclear(res);
            return;
        }
        i = 0;
        bytea = PQgetvalue(res, i, 0);
        index = atoi(bytea);
        PQclear(res);
        switch (index){
        case 0: strcpy(string, "SQL_ASCII"); break;
        case 1: strcpy(string, "EUC_JP"); break;
        ...
        case 33: strcpy(string, "GB18030"); break;
        }
        *var_len = strlen(string);
        return (unsigned char *) string;

*       // 3 - THIS **DONT **WORK (retrieving bool)
***      
        long_ret = 0;
        strcpy(query_string, "SELECT datistemplate FROM pg_database 
limit 1 offset 0");
        res = PQexec(conn, query_string);                 
        if (PQresultStatus(res) != PGRES_TUPLES_OK){
            fprintf(stderr, "SELECT query failed [%s].\n", query_string);
            PQclear(res);
            return;
        }
        i = 0;
        bytea = PQgetvalue(res, i, 0);
        long_ret = atol(bytea);
       
        return (unsigned char *) &long_ret;

How can I retrieve a bool data type (code 3)?
How can I return for a string C data type (return (unsigned char *) 
&long_ret;)
and the last question
although working, its correct list code 1 and list code 2?
anybody has code sample to share (mail me)?

thank you for any help, my deadline paper is near and has proposed the 
open source MIB for postgresql database!
thank you!

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