[Lazarus] Library function trashing object

[Lubos Pintes]

I think you could not declare the second parameter of GetData as var 
parameter. Because it is then treated as address.
I am not sure what corresponds to C++ unsigned long, perhaps LongWord?
So try to change the second parameter so that it is not a var parameter.
Dňa 19. 4. 2013 19:18 Leonardo M. Ramé wrote / napísal(a):
> I'm using a C++ library with a function that receives a parameter this
> way:
>
> int getData(void * &buffer, unsigned long &bufSize){
>    bufSize = 10;
>    return 1;
> }
>
> The Pascal definition I'm using is this:
>
> function (var buffer: pointer; var bufsize: longword): Integer; cdecl;
>
> I'm using this library without any issue in a couple of programs, but in
> this new program, after the "bufSize" variable is assigned (inside the
> library) an object of my Lazarus program is trashed. Weird.
>
> The instance of my object (an very simple TCustomControl descendant) is
> declared in a TForm class, as FMyControl: TMyControl, then created an
> instance in TForm's constructor. In another method of TForm, I call the
> library's function then I try to use a method of FMyControl, but it
> gives a SigSegv.
>
> Example:
>
> procedure TForm1.doSomething;
> var
>    lBuffer: PWord;
>    lBufSize: longword;
> begin
>    lBuffer := nil;
>    lBufSize := 0;
>    FMyControl.call_some_method; // FMyControl has debugging info.
>    getData(lBuffer, lBufSize);
>    FMyControl.call_some_method; // FMyControl "cannot access memory address...SIGSEGV"
> end;
>
> I can modify the C++ function if needed. Am I incorrectly declaring the
> function params?. Why is FMyControl's memory position trashed?.
>
> Regards,