Re: [GENERAL] PQgetvalue weirdness

On Thu, 10 Sep 1998, Chris Johnson wrote:

> I usually use pg_result... here is a snipped of some C I have used:
>
> <<<>>>
>   for (i = 0; i < PQntuples(res); i++)
>     {
>       dbName = PQgetvalue(res, i, 0);
> <<<>>>
>
> It works perfectly on the Linux, IRIX and Digital Unix (OSF/1)... Assuming
> all the regression tests worked when you installed, and that you are
> linking your program with the proper libpq, I guess the next step is to
> see more of the code and to know exactly how you compiled it.

I'm running Linux (RH4.2, 2.0.34) , latest version of pg (6.3.2?) and
linking AFAIK with
the correct libpq.a - I only have the one copy on my system so it should
be correct. The code is below. Everything else works but for the
getvalue()


dbresult is just a list-type structure with char* and dbresult* members.
dbconn is pre-initialised in another function.

Note: code has been stripped of non-essential stuff.

/* This function returns a _single_ column value from a table
 * The return value is a list to allow multiple results
 * When you've finished with the returned list, call db_freevalue(list)
 */
dbresult * db_getvalue(char * table, char * column, char * where_clause)
{
  dbresult        *values, *v;
  char            query[1024]; /* max is 8192 */
  PGresult        *result;
  ExecStatusType    status;
  int            tuples;
  int            count = 0;

  if (!table || !column) return NULL;


  sprintf(query, "SELECT %s FROM %s", column, table);


  if (where_clause) sprintf(query, "%s %s", query, where_clause);


  result = PQexec(dbconn, query);


  if ((status = PQresultStatus(result)) != PGRES_TUPLES_OK) {

    char temp[1024];
    sprintf(temp, "SELECT returned %s\n  Query was: %s",
            PGerror[status], query);
/*    logerr("DB", temp); */

    return NULL;
  }



  tuples = PQntuples(result);

  values = malloc(sizeof(dbresult));
  v = values;


  count = 0;


  PQprintTuples(result, stderr, 1, 1, 0);
  while (count <= tuples) {

/*
    v->data = malloc(PQgetlength(result, count, 1));
*/
    v->data = malloc(256);
    v->next = NULL;


    strcpy(v->data, PQgetvalue(result, count, 1));

    if (--count > 0) {
      v->next = malloc(sizeof(dbresult));
      v = v->next;
    }
  }

  PQclear(result);
  return values;


}


Simon.


>
> Chris
>
> --
> A language that doesn't affect the way you think about programming is
> not worth knowing.
>
> On Thu, 10 Sep 1998, Simon Drabble wrote:
>
> >
> >
> > On Thu, 10 Sep 1998, Chris Johnson wrote:
> >
> > > Postgres numbers the rows and fields starting at 0 - your call to get the
> > > first row and column would be PQgetvalue(result, 0, 0)
> > >
> > > Chris
> >
> > Thanks for your reply, but..
> >
> > If I have a zero for the field number (last parameter) I get a seg fault
> > immediately - gdb shows it to be in PQgetvalue().
> >
> > If I have a row number of zero (second param) I get the same error as
> > below (if the column number is >0 )
> >
> >
> > Simon.
> >
> >
> >
> >
> > >
> > > On Thu, 10 Sep 1998, Simon Drabble wrote:
> > >
> > > >
> > > > I'm executing a (simple) query using libpq, and this is the error I get
> > > > from PQgetvalue(result, 1, 1):
> > > >
> > > > PQgetvalue: There is no field 1 in the query results.  The highest
> > > > numbered field is 0.
> > > >
> > > > I get a similar error if I call getlength().
> > > >
> > > > There _is_ data there - PQprintTuples() prints everything correctly.
> > > >
> > > >
> > > > Can anyone shed any light?  PQtrace() doesn't reveal anything useful..
> > > >
> > > >
> > > > Simon.
> > > >
> > > >
> > > > --
> > > >                            ...oooOOOooo...
> > > >    Simon Drabble                     mailto:madlather@syspac.com
> > > >    http://fiddletrudge.dyn.ml.org/
> > > >    KreatAPayj           --        ~simon/KreatAPayj/login.html
> > > >    LizardCam            --        LizardCam/LizardCam.html
> > > >    Linux Knowledge Base --        ~simon/LinuxKB/index.html
> > > >
> > > >
> > > >
> > >
> >
> > --
> >                            ...oooOOOooo...
> >    Simon Drabble                     mailto:madlather@syspac.com
> >    http://fiddletrudge.dyn.ml.org/
> >    KreatAPayj           --        ~simon/KreatAPayj/login.html
> >    LizardCam            --        LizardCam/LizardCam.html
> >    Linux Knowledge Base --        ~simon/LinuxKB/index.html
> >
> >
>

--
                           ...oooOOOooo...
   Simon Drabble                     mailto:madlather@syspac.com
   http://fiddletrudge.dyn.ml.org/
   KreatAPayj           --        ~simon/KreatAPayj/login.html
   LizardCam            --        LizardCam/LizardCam.html
   Linux Knowledge Base --        ~simon/LinuxKB/index.html