Thread: Creating HeapTuple from char and date values

Creating HeapTuple from char and date values

From

Amin

Date:

07 December 2022, 05:06:31

Hi All,

I am trying to create HeapTuple data structure.

First, I create a tuple descriptor:
     TupleDesc *td=CreateTemplateTupleDesc(colCount);
Then, for each variable, I do:
      TupleDescInitEntry(*td,v->varattno,NULL,v->vartype,v->vartypmod,0);
Then, I assign values:
      if int32: values[v->varattno-1]=Int8GetDatum(myValue);
Similarly for float.
Finally, I create the HeapTuple:
      HeapTuple tuple=heap_form_tuple(td,values,isnull);

Everything works fine with int and float. But I don't know how to handle chars.
Let's say we have a character(10) column. One problem is v->vartypmod will be set to 14. Shouldn't it be 10?
Second, how should I assign values? Is values[v->varattno-1]=CStringGetDatum(myValue); correct? Should I set the last parameter to TupleDescInitEntry? Why am I getting "invalid memory alloc request size" or segfault with different configurations?

Re: Creating HeapTuple from char and date values

From

Ashutosh Bapat

Date:

08 December 2022, 16:15:52

On Thu, Dec 8, 2022 at 12:56 AM Amin <amin.fallahi@gmail.com> wrote:
>
> Hi All,
>
> I am trying to create HeapTuple data structure.
> First, I create a tuple descriptor:
>      TupleDesc *td=CreateTemplateTupleDesc(colCount);
> Then, for each variable, I do:
>       TupleDescInitEntry(*td,v->varattno,NULL,v->vartype,v->vartypmod,0);
> Then, I assign values:
>       if int32: values[v->varattno-1]=Int8GetDatum(myValue);
> Similarly for float.
> Finally, I create the HeapTuple:
>       HeapTuple tuple=heap_form_tuple(td,values,isnull);
>
> Everything works fine with int and float. But I don't know how to handle chars.
> Let's say we have a character(10) column. One problem is v->vartypmod will be set to 14. Shouldn't it be 10?

I think the 4 extra bytes is varlena header - not sure. but typmod in
this case indicates the length of binary representation. 14 looks
correct.

> Second, how should I assign values? Is values[v->varattno-1]=CStringGetDatum(myValue); correct? Should I set the last
parameterto TupleDescInitEntry? Why am I getting "invalid memory alloc request size" or segfault with different
configurations?

is myValue a char *?
I think you need to use CStringGetTextDatum instead of CStringGetDatum.

-- 
Best Wishes,
Ashutosh Bapat