Subject Re: [firebird-support] UDF - reading BLOB length
Author Josef KokeŇ°
Nice - this will also fail with the same error:

function BLOBLEN(Value: PBlob): Integer; cdecl;
begin
Result := 1;
end;

I admit I find this very mystifying.

Josef

> Hi!
>
> What could possibly be wrong with the following UDF?
>
> * Function *
>
> type
> TBlob = {packed} record
> GetSegment: TISC_BlobGetSegment;
> BlobHandle: PInt;
> SegmentCount: LongInt;
> MaxSegmentLength: LongInt;
> TotalSize: LongInt;
> PutSegment: TISC_BlobPutSegment;
> end;
> PBlob = ^TBlob;
>
> function BLOBLEN(Value: PBlob): Integer; cdecl;
> begin
> if Value = nil then
> Result := 0
> else
> Result := Value^.TotalSize;
> end;
>
> * Declaration *
>
> DECLARE EXTERNAL FUNCTION BLOBLEN
> BLOB
> RETURNS INTEGER
> ENTRY_POINT 'BLOBLEN' MODULE_NAME 'pwIBUDF';
>
> * Usage *
>
> SELECT BLOBLEN(someblobfield) FROM sometable
>
> I expect to get a list of lengths of a particular BLOB field in the
> table. In reality, I get an error on Firebird 1.5, 2.1 and 2.5. Error
> log of FB 2.5 says:
>
> The user defined function: BLOBLEN
> referencing entrypoint: BLOBLEN
> in module: pwIBUDF
> caused the fatal exception: Access violation.
> The code attempted to access a virtual
> address without privilege to do so.
> This exception will cause the Firebird server
> to terminate abnormally.
>
> Which seems rather strange, considering that Firebird was supposed to
> pass me a valid BLOB descriptor - and in fact, in a similar function
> (but one which returns BLOB contents as a string) apparently does.
>
> I'd welcome any pointers (no pun intended).
>
> Thanks,
>
> Josef
>
>
> ------------------------------------
>
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>
> Visit http://www.firebirdsql.org and click the Resources item
> on the main (top) menu. Try Knowledgebase and FAQ links !
>
> Also search the knowledgebases at http://www.ibphoenix.com
>
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> Yahoo! Groups Links
>
>
>