Newbie problem with from database in C - Mailing list pgsql-interfaces

From clarkhorse@clarktx.com
Subject Newbie problem with from database in C
Date
Msg-id W5749323096104921211159632@webmail12
Whole thread Raw
Responses Re: Newbie problem with from database in C  ("Jonah H. Harris" <jonah.harris@gmail.com>)
List pgsql-interfaces
I have been trying to use use libpq interface to get data from PostgreSQL to a C variable.  I started reading through the book PostgreSQL 2nd Edition by Korry and Susan Douglas and ran into a snag as soon as I started trying to read numbers into variables.
I started with int32 datatypes which they used in their example, then tried int and int4 then int 16 and int2 which is what they used in there example

by table testing has the data types
idno integer
runname character varying (5)

That is all I put into it for testing.

characters are fine so far.  I have placed the code I am using below. 
Would appreciate it if someone could tell me what is wrong or provide me with a reference on how to do this properly.

The code below is marked as '/////Debug' so I could find it and make changes trying to figure out what is going on


Thanks,

--------------------------------------------------------------------------------------------

/*
** File: client3d.c
*/

#include <stdlib.h>
#include <string.h>
#include <stdarg.h>


#include <libpq-fe.h>
#include <postgres.h>
#include <utils/date.h>

#define MAX_PRINT_LEN   40

static bool status_ok( PGresult * result )
{
    ExecStatusType  status = PQresultStatus( result );

    if( status == PGRES_TUPLES_OK || status == PGRES_COMMAND_OK )
        return( TRUE );
  else
      return( FALSE );
}

static PGresult * exec_sql( PGconn * conn, bool destroy_result, const char * text, ... )
{
    char        buf[2048];
    va_list     args;
    PGresult *  result;

    va_start( args, text );
    vsnprintf( buf, sizeof( buf ), text, args );

    result = PQexec( conn, buf );

    if( destroy_result == TRUE )
    {
        if( status_ok( result ) == FALSE )
        {
            fprintf( stderr, "%s\n%s\n", buf, PQresultErrorMessage( result ));
            exit( -1 );
        }

        PQclear( result );
        return( NULL );
    }
    else
        return( result );
}


static char separator[MAX_PRINT_LEN+1];

void print_result_set( PGresult * result )
{
  int          col;
  int          row;
  int        * sizes;

/*
**  Compute the size for each column
*/
  sizes = (int *)calloc( PQnfields( result ), sizeof( int ));

  for( col = 0; col < PQnfields( result ); col++ )
  {
    int len = 0;

    for( row = 0; row < PQntuples( result ); row++ )
    {
      if( PQgetisnull( result, row, col ))
        len = 0;
      else
        len = PQgetlength( result, row, col );

      if( len > sizes[col] )
        sizes[col] = len;
    }
    if(( len = strlen( PQfname( result, col ))) > sizes[col] )
      sizes[col] = len;

    if( sizes[col] > MAX_PRINT_LEN )
      sizes[col] = MAX_PRINT_LEN;
  }

/*
**  Print the field names.
*/
  for( col = 0; col < PQnfields( result ); col++ )
  {
    printf( "%-*s ", sizes[col], PQfname( result, col ));
  }

  printf( "\n" );

/*
**  Print the separator line
*/
  memset( separator, '-', MAX_PRINT_LEN );

  for( col = 0; col < PQnfields( result ); col++ )
  {
    printf( "%*.*s ", sizes[col], sizes[col], separator );
  }

  printf( "\n" );

/*
**  Now loop through each of the tuples returned by
**  our query and print the results.
*/
  for( row = 0; row < PQntuples( result ); row++ )
  {
    for( col = 0; col < PQnfields( result ); col++ )
    {
      if( PQgetisnull( result, row, col ))
        printf( "%*s", sizes[col], "" );
      else
        printf( "%*s ", sizes[col], PQgetvalue( result, row, col ));
    }
    printf( "\n" );

  }
  printf( "(%d rows)\n", PQntuples( result ));
  free( sizes );
}
/////////////Debug
//////////This is the function that prints out the data
void print_binary_result_set( PGresult * result )
{
  int           row;
  int32         * idno;
  char          * runname;

  for( row = 0; row < PQntuples( result ); row++ )
  {
      idno      = (int32 *)PQgetvalue( result, row,0);
      runname     = (char *)PQgetvalue( result, row,1);
      printf( "%d %8.8s  \n",* idno , runname);
  }
}

void process_query( PGconn * connection, const char * query_text )
{
  PGresult      *       result;

#if 0
  if(( result = PQexec( connection, query_text )) == NULL )
  {
    printf( "%s\n", PQ:errorMessage( connection ));
    return;
  }
#else

  exec_sql( connection, TRUE, "BEGIN TRANSACTION" );
 //////////////Debug
 exec_sql( connection, TRUE, "DECLARE mycursor BINARY CURSOR FOR SELECT * FROM testing" );
  result = exec_sql( connection, FALSE, "FETCH ALL FROM mycursor" );

#endif
  if( PQresultStatus( result ) == PGRES_TUPLES_OK )
  {
      if( PQbinaryTuples( result ))
        print_binary_result_set( result );
      else
        print_result_set( result );
  }
  else if( PQresultStatus( result ) == PGRES_COMMAND_OK )
  {
    printf( "%s", PQcmdStatus( result ));

    if( strlen( PQcmdTuples( result )))
      printf( " - %s rows\n", PQcmdTuples( result ));
    else
      printf( "\n" );
  }
  else
  {
      printf( "%s\n", PQresultErrorMessage( result ));
  }

  PQclear( result );

  exec_sql( connection, TRUE, "END TRANSACTION" );

}

int main( int argc, char * argv[] )
{
  PGconn * connection;

  if( argc != 2 )
  {
    printf( "usage  : %s \"connection-string\"\n", argv[0] );
    printf( "example: %s \"user=myname password=cows\"\n", argv[0]);
    exit( 1 );
  }

  if(( connection = PQconnectdb( argv[1] )) == NULL )
  {
    printf( "Fatal error - unable to allocate connection\n" );
    exit( 1 );
  }

  if( PQstatus( connection ) != CONNECTION_OK )
    printf( "%s\n", PQerrorMessage( connection ));
  else

/////Debug
    process_query( connection, "SELECT * FROM testing" );

  PQfinish( connection );

  exit( 0 );
}









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