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Re: C-Function: Returning Rows

From: Carel Combrink <s25291930(at)tuks(dot)co(dot)za>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: PostgreSQL Novice List <pgsql-novice(at)postgresql(dot)org>
Subject: Re: C-Function: Returning Rows
Date: 2010-05-10 15:49:34
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Lists: pgsql-novice
Quoting Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:

> Carel Combrink <s25291930(at)tuks(dot)co(dot)za> writes:
>> in my function I have the following:
>>      TupleDesc tup_descriptor;
>>      Datum dat_values[2];
>>      HeapTuple heap_tuple;
>>      bool *pNulls;
>>      get_call_result_type(fcinfo, NULL, &tup_descriptor);
>>      BlessTupleDesc(tup_descriptor);
>>      dat_values[0] = Int32GetDatum(50);
>>      dat_values[1] = Int32GetDatum(20);
>>      iTup_Length = tup_descriptor->natts;
>>      pNulls = palloc(iTup_Length * sizeof(bool));
>>      heap_tuple = heap_form_tuple(tup_descriptor, dat_values, pNulls);
>>      PG_RETURN_DATUM(HeapTupleGetDatum(heap_tuple));
>> Am I doing something wrong in my function that would have this affect?
> Failing to initialize the values of pNulls[], no doubt.
> It would also be a good idea to check for a failure result from
> get_call_result_type.
> BTW, what's the rationale for using a fixed-length Datum array and
> a variable-length nulls array?  Usually people handle both of those
> the same way.
> 			regards, tom lane

I've added a line to initialize the values like follow:

    malloc(pNulls, false, iTup_Length * sizeof(bool));

and it works perfectly each time.

As for checking the failure result: I did not put it in my email but  
actually I am checking to see if it is not "TYPEFUNC_COMPOSITE".

I did use a fixed-length nulls array but somewhere in my  
testing/frustration I mixed the two (I played with various options).

I noted, if using fixed-length nulls array I should set the array to  
false also otherwise the same is experienced. Is this supposed to  
happen this way? Is there documentation on this, I tried googling the  
function with no success?

Thank you Tom,
Carel Combrink

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