Re: Convert Datum* to char*

On 01/06/2014 03:09 PM, Masterprojekt Naumann1 wrote:
> I want to read an attribute value from a TupleTableSlot. When I try to
> convert an attribute of SQL type varchar from Datum* to char* with the help
> of the method TextDatumGetCString(...), sometimes there is a segmentation
> fault. The segmentation fault comes from the method
> TextDatumGetCString(...), which is defined in utils/builtins.h.
> Unfortunately, the fault is not always reproducible. I debugged the code
> and figured out that the value of result->tts_values[i] sometimes is
> random. It may be uninitialized memory. In other cases, the variable value
> is NULL. Then, I can just skip the conversion from Datum* to char*, so that
> there is no segmentation fault. I attached a patch with the code. The
> relevant line is:
> char *value = TextDatumGetCString(result->tts_values[i]);
> The SQL-Query is a simple "SELECT * from ..." on the TPC-H table customer.
> About every third execution leads to a segmentation fault.

Maybe the field is NULL? By convention, we normally set the Datum to 0
on an SQL NULL, but you're supposed to check tts_isnull first, and
ignore tts_values[x] when tts_isnull[x] is true.

- Heikki