converting datum to numeric

Hello

2013/6/25 Szymon Guz <mabewlun@gmail.com>:

Hi,
I've got a couple of questions.

I was using numeric_out like this:

DatumGetCString(DirectFunctionCall1(numeric_out, d));

Why do I have to use DirectFunctionCall1 instead of calling numeric_out?

numeric_out functions doesn't use C calling convention - it use own
convention for support NULL values and some other informations.
DirectFunctionCall1 is simple function that transform C like call to
PostgreSQL call. You can do it directly, but you have to prepare
necessary structures.

I was suggested to use numeric_send instead of numeric_out, however when
changing the function names in the above example, the whole expression
returns 8. Always 8. I check with:

char *x = DatumGetCString(DirectFunctionCall1(numeric_send, d));
PLy_elog(NOTICE, x).

"send" functions are used for binary protocol - so it is nonsense.

And my main question: is there any documentation about those internal
functions, which use and when etc?

source code :( and http://www.postgresql.org/docs/9.2/static/xfunc-c.html

src/backend/utils/atd/* is very useful and contains lot of materials for study

some examples of usage you can find in contrib examples

http://www.postgresql.org/docs/9.2/static/extend.html

Regards

Pavel

thanks
Szymon

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On 25 June 2013 08:51, Pavel Stehule <pavel.stehule@gmail.com> wrote:

Hello

2013/6/25 Szymon Guz <mabewlun@gmail.com>:

Hi,
I've got a couple of questions.

I was using numeric_out like this:

DatumGetCString(DirectFunctionCall1(numeric_out, d));

Why do I have to use DirectFunctionCall1 instead of calling numeric_out?

numeric_out functions doesn't use C calling convention - it use own
convention for support NULL values and some other informations.
DirectFunctionCall1 is simple function that transform C like call to
PostgreSQL call. You can do it directly, but you have to prepare
necessary structures.

I was suggested to use numeric_send instead of numeric_out, however when
changing the function names in the above example, the whole expression
returns 8. Always 8. I check with:

char *x = DatumGetCString(DirectFunctionCall1(numeric_send, d));
PLy_elog(NOTICE, x).

"send" functions are used for binary protocol - so it is nonsense.

Hi,
thanks for the information. So I will leave speeding it up for this moment.

thanks,
Szymon