Re: Extracting data from BYTEA column to binary file using libpq

On Tue, Sep 14, 2010 at 6:01 PM, Julia Jacobson <julia(dot)jacobson(at)arcor(dot)de> wrote:
> Hello everybody out there using PostgreSQL,
>
> What is the problem with the following C++ code for the extraction of data
> from a BYTEA column to a binary file?
>
> #include <stdlib.h>
> #include <stdio.h>
> #include <iostream>
> #include <fstream>
> #include "libpq-fe.h"
> using namespace std;
>
> main ()
> {
>  PGconn *conn;
>  conn = PQconnectdb("hostaddr='databaseserver.com' port='5432'
> dbname='test_db' user='test_user' password='secret'");
>  int size;
>  const char* contents;
>  PGresult* res;
>  res = PQexecParams(conn,
>  "SELECT filecontent FROM pictures WHERE picture_id='3'",
>  0, NULL,NULL,NULL,NULL,
>  1);
>
>  if (res && PQresultStatus(res)==PGRES_TUPLES_OK)
>  {
>    size = PQgetlength(res, 0, 0);
>    contents = PQgetvalue(res, 0, 0);
>  }
>  ofstream myFile ("picture.jpg", ios::out | ios::binary);
>  myFile.write (contents);
>  myFile.close();
> }
>
> Thanks in advance,
> Julia
>
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Hi,

In addition to what Daniel Verite said, I think you should use numeric
IP address instead of the host name, or consider replacing 'hostaddr'
with 'host' if you plan to use host names.
'hostaddr' is meant to be used when you want to avoid the name resolution step.

conn = PQconnectdb("host='databaseserver.com' port='5432'
dbname='test_db' user='test_user' password='secret'");

regards,

diego