Thanks for the explanation and example, Arno, but I was 1 step ahead of you in realising the mistake.
What I did (which appears to have worked as the errors are not being reported now) is to simply move the "Note" variable into the global scope. The DLL only gets called by one external process so I think it's a reasonably safe approach... unless you know different. :-) Regards, Adam -----Original Message----- From: twsocket-boun...@elists.org [mailto:twsocket-boun...@elists.org] On Behalf Of Arno Garrels Sent: 16 September 2011 07:17 To: ICS support mailing Subject: Re: [twsocket] DLL implementation advice (or example)... Adam Burgoyne wrote: > I've now changed the > code to this which should solve the problem if I understood correctly: > > function ReadMessage: PAnsiChar; stdcall; var > Note: AnsiString; > begin > EnterCriticalSection(CritSectn); > > if (NotesList.Count > 0) then > begin > Note := NotesList.Strings[0]; > NotesList.Delete(0); > Result := PAnsiChar(Note); > end > else > Result := ''; > > LeaveCriticalSection(CritSectn); > end; That doesn't work either, the string assigned to the local variable is destroyed when it goes out of scope, that is when the function is left. You have to change the function like below and have the caller allocate and free the memory the string is copied to: {code untested} function ReadMessage(pBuf: PAnsiChar; pBufSize: PLongWord): LongWord; stdcall; begin try EnterCriticalSection(CritSectn); try if pBufSize = nil then begin Result := 0; end else if pBuf = nil then begin // Return required size / number of AnsiChars pBufSize^ := Length(NotesList[0]); Result := 0; end else if pBufSize^ < Length(NotesList[0]) then begin // Return required size / number of AnsiChars pBufSize^ := Length(NotesList[0]); Result := 0; end else begin // Return number of copied AnsiChars Result := Length(NotesList[0]); Move(Pointer(NotesList[0])^, pBuf^, Result); NotesList.Delete(0); end; finally LeaveCriticalSection(CritSectn); end; except Result := 0; end; end; {code} But.. If that function is called from different threads you cannot use it to get the size of a string in a first call with a nil pBuf since on the second call the string might no longer be the same. -- Arno Garrels -- To unsubscribe or change your settings for TWSocket mailing list please goto http://lists.elists.org/cgi-bin/mailman/listinfo/twsocket Visit our website at http://www.overbyte.be -- To unsubscribe or change your settings for TWSocket mailing list please goto http://lists.elists.org/cgi-bin/mailman/listinfo/twsocket Visit our website at http://www.overbyte.be
