String returned by your UDF must be allocated using this function

function ib_util_malloc(size: LongWord): Pointer; external 'ib_util.dll';

and you have to instruct Firebird to release the memory using FREE_IT keyword:

... RETURNS CSTRING(100) FREE_IT ...


Ivan
http://www.volny.cz/iprenosil/interbase/

----- Original Message -----
From: "Martin Dew" <martin.dew@...>
To: <firebird-support@yahoogroups.com>
Sent: Wednesday, January 05, 2005 2:17 PM
Subject: [firebird-support] UDF Assistance


>
> I basically have some VARCHAR(8192) fields which I only want to return a
> maximum of 100 characters from them (large Data to fetch on some
> queries) ..
>
> I have written a UDF in Delphi ( library and Unit file below ) to do
> this through a function called OWL_STRLEFT100.
>
> I have declared it using;
>
> declare external function OWL_STRLEFT100
> CSTRING(8192) CHARACTER SET NONE,
> integer
> returns
> CSTRING(100) CHARACTER SET NONE
> entry_point 'OWL_STRLEFT100' module_name 'OwlUDFs.dll';
>
>
> however, when I try to run it say for example;
>
> select OWL_STRLEFT100(symptoms,1) from sp_patlogview
>
> It crashes the connection (error message "Connection lost to database").
>
> I am assuming I have done something wrong here, could anyone help me out
> and point out the errors of my ways ?
>
> Thanks in advance.
> Martin
>
> -----
>
> library OwlUDFs;
>
> { Important note about DLL memory management: ShareMem must be the
> first unit in your library's USES clause AND your project's (select
> Project-View Source) USES clause if your DLL exports any procedures or
> functions that pass strings as parameters or function results. This
> applies to all strings passed to and from your DLL--even those that
> are nested in records and classes. ShareMem is the interface unit to
> the BORLNDMM.DLL shared memory manager, which must be deployed along
> with your DLL. To avoid using BORLNDMM.DLL, pass string information
> using PChar or ShortString parameters. }
>
> uses
> SysUtils,
> Classes,
> OwlUDF in 'OwlUDF.pas';
>
> {$R *.RES}
>
> exports
> OWL_STRLEFT100;
>
> begin
> end.
>
>
> -----
>
>
> unit OwlUDF;
>
> interface
>
> function OWL_STRLEFT100(var sz: PChar; var cnt: Integer): PChar;
> cdecl; export;
>
> implementation
>
> function OWL_STRLEFT100(var sz: PChar; var cnt: Integer): PChar;
> Var
> i : integer;
> s : String;
> begin
> if (sz = nil) then begin
> result := nil
> end
> else if (cnt = 0) then begin
> result := nil
> end
> else begin
> if (cnt >= 100) then
> i := 99
> else
> i := cnt;
>
> s := copy(sz,0,i);
> result := PChar(s);
> end;
> end;
>
> end.