[fpc-pascal] C++ > C wrapper callback > Pascal Continues

[Peter Vreman]

>> Urbansound wrote:
>>> Hi List,
>>>    A Windows pascal application is recieving data from a C++, VisC API,
>>> which is set up as a class, and a conventional C wrapper, attempting to
>>> extend functionality into Pascal.  C++ and C are vis 4.2 MFC
>>>
>>> function L1_Callback(quote : pointer) : integer; stdcall; export;
>>
>> One thing that comes into my mind is that you should make sure that
>> "integer" above really means what you want. "integer" is either 16-bit
>> or 32-bit,
>> Also, do you really want to put "export" here ? It's harmless, but
>> unnecessary, if you're only passing a pointer to L1_Callback to some
>> other C routine.
>
> Thank you to Michalis Kamburelis...
>
> clipped this down (and still too long)...
>
> Yes the integer sizes were confirmed = 32 (win32 gui) and the export was
> added simply attempting to force a change in memory allocation, along with
> pre-initializing variables.  Among other things, Delphi mode was tried and
> we boiled the problem down to two lines of code in particular, commented
> below.  As well, we hand converted the Pascal app to C, in order to test
> the
> C_wrapper, compiled on GCC and the same calling conventions and methods
> work
> fine in C-GCC, but fail in Pascal.  VERY ODD. Wrapper works fine.
>
> Review:
> //------------------------------
> PROBLEM IS BELOW and either comment line removed, will crash = RT217...
> I suspect the problem is pointer "quote", somehow is crashing registers.
>
> FUNCITON HEADER:
> function SetL1Callback(func_addr : pointer) : integer; stdcall; external
> 'DasRapper.dll' name 'SetL1Callback';
>  >>>>> where SetL1Callback(@L1_Callback); is set in the pascal main
> area.<<<<<
>
> FUNCTION CALL TO WRAPPER
> function L1_Callback(quote : pointer) : integer; stdcall;
> var
>     bid_price : double = 0.0;
>     s : ansistring = '';
> begin
>     SendMessage(listbox, LB_ADDSTRING, 0, longint(pchar('L1 Callback')));
>     SendMessage(listbox, LB_ADDSTRING, 0, longint(Get_secsym(quote)));
>     bid_price := Get_l1_BidPrice(quote);
>
>     //s := FloatToStr(bid_price); // This will crash!
>     //SendMessage(listbox, LB_ADDSTRING, 0, longint(pchar(@s)));
> end;
>
> //------------------------------------
> PASCAL WRAPPER function being called is below
>
> DllExport void SetL1Callback(TL1Callback p) { DasApi.m_pL1Callback=p; };
>
> SUMMARY:
> There  seems to be nothing I can find that would cause a Runtime 217 in
> the
> layout and now finding C conversion of same is working.
>
> Can anyone else please confirm if this should work, or is a bug report be
> in
> order??

A bug report is only in order if there are complete sources otherwise it
can't be reproduced.


> Thanks to all, whoever may have additional ideas.     Mike

Are the pascal units are initialized? A call to FPC_INITIALIZEUNITS is
required otherwise the memorymanager etc. will not work.