Getting Jpeg error #51 when loading from BLOB with Delphi 2010, fine w Delphi 2006

I have an old application developed in Delphi 2006 that I now needed to make some changes in.

In this app, I'm loading images from a MsSQL "image" field but when i compile with delphi 2010 I get the error : "raised exception class EJPEG with message 'JPEG error #51'."

The code that get's the image from the database:

aStream := TMemoryStream.Create;
Try
If LoadFromBlob(FieldByName('Picture'), aStrea开发者_开发技巧m) then
begin
    Pic:=TJpegImage.Create;

    try
        Try
            Pic.LoadFromStream(aStream);
            Picture.Assign(Pic); // <------ JPEG Error #51 here w D2010
        Except
            //something went wrong loading
            HandleImageError();    
        End;

    finally
     Pic.Free;
    end;

end;
Finally
    aStream.Free;
End;

// ............

function LoadFromBlob(const AField: TField; const Stream: TStream): boolean;
var
    ResultStr: string;
    PResultStr: PChar;
begin
    Result := false;
    if (Assigned(AField)) and (Assigned(Stream)) then begin
        try
            ResultStr := AField.Value;
            If ResultStr <> '' then
            begin
                PResultStr := PChar(ResultStr);
                Stream.Write(PResultStr^, Length(ResultStr));
                Stream.Seek(0,0);
                Result := true;
            end;
        except
        end;
    end;
end;

Googled around a bit and found out that error #51 means: JERR_NO_QUANT_TABLE, whatever that means.

When I compile with Delphi 2006, the same code works fine with no errors, so what's going wrong with D2010?

In D2010 Char changed from Ansi to Unicode, which means it occupies two bytes instead of one. Change your variables in LoadFromBlob to AnsiString and PAnsiChar and it should work.

Update: Instead of Field.Value (Variant) you should better access Field.AsAnsiString; The variant access might include an implicit Unicode->Ansi conversion which introduces the error.

You are using a rather awkward way to save a blob field to a stream. Why are you not using TBlobField.SaveToStream ?

Save your aStream out to a file and examine with a hex editor. Compare the D2006 and D2010 results. What you find there should convince you that it's nothing to do with the JPEG header, and it's likely a Unicode/Widechar issue.

Why going the way over the strings anyway? What about directly writing to the stream? The image field probably is a TBlobField or TGraphicField. Those have a SaveToStream method that would perfectly suit your needs.