Thanks Pavel for your elaborate answer. I think it was spot on. :-)

A couple of followup questions though. If I let FB allocate memory the
way you said, does the max length specified in the DECLARE control how
much memory FB allocates?

So, if I do this:

> -----
> procedure myUDF(InStr: PChar; var OutStr: PChar); cdecl; export;
> begin
> // check if OutStr<>nil - then FB has allocated the memory
> // processing
> ...
> end;
> -----
> DECLARE EXTERNAL FUNCTION myudffunc
> CSTRING(10), CSTRING(10)
> RETURNS PARAMETER 2
> ENTRY_POINT 'myUDF' MODULE_NAME 'myudfmodule';
> -----

Will myUDF cause buffer overruns if it writes more than 10 characters +
0 terminator into the OutStr buffer?

In that case, it would be tempting to declare with the maximum size
which I think I read is 32767:

-----
DECLARE EXTERNAL FUNCTION myudffunc
CSTRING(10), CSTRING(32767)
RETURNS PARAMETER 2
ENTRY_POINT 'myUDF' MODULE_NAME 'myudfmodule';
-----

But I assume this would impact performance since it has to allocate a
lot more memory on each call. Right? Would this impact be big? I mean,
the buffer would be released as soon as the value is returned to the
client in a dataset or written into a field, woudln't it? So it wouldn't
really waste more than one such buffer at a time. (Per concurrent query
that uses that UDF, that is.)

Thanks,
Kjell
--
--------------------------------------
Kjell Rilbe
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E-post: kjell.rilbe@...
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