Re: Weird problems with C extension and bytea as input type

On Tue, Mar 22, 2011 at 16:07, Merlin Moncure <mmoncure(at)gmail(dot)com> wrote:
> On Tue, Mar 22, 2011 at 8:22 AM, Adrian Schreyer <ams214(at)cam(dot)ac(dot)uk> wrote:
>> Hi,
>>
>> I have a weird problem with my custom functions (written in C,C++)
>> that use bytea as input type (cstring works fine). The functions will
>> work as expected if they are the only function that uses the bytea
>> column in a query; as soon as there is a second function using the
>> same column, the C function will return one of the following: an empty
>> cstring, a substring of the bytea or the correct cstring. Based on
>> these symptoms I assume there is something fundamental that I do wrong
>> (or that is missing) with handling the bytea pointer.
>>
>> In one specific example, the bytea contains a binary file format that
>> the function converts into a string format. I convert the bytea to a
>> C++ string with string(VARDATA(b), VARSIZE(b)-VARHDRSZ).
>>
>> bytea *b = PG_GETARG_BYTEA_P(0);
>> char *ism;
>>
>> ism = function(b);
>>
>> PG_RETURN_CSTRING(ism);
>
> your problem is probably inside 'function' -- are you properly copying
> the data out of the bytea struct?.  also, are you really sure you want
> to be returning cstring type, not text?
>
> merlin
>

yes, the function in the C++ toolkit I use takes a std::string as
input. So far I have used string(VARDATA(oeb), VARSIZE(oeb)-VARHDRSZ)
to convert it. I want to change both input and output to text later on
once this is working. I suspect I will get similar problems with
pg_getarg_text_p() or any other struct. I think you are right, I am
not coping the data out of the struct correctly; all my functions that
use VARDATA() have these problems. What would be the proper way?

Cheers,

Adrian