O/H David Bolton έγραψε:
> I've been writing a little test harness to test C and C++ dlls. It's for
> this btw.
> http://cplus.about.com/od/programmingchallenges/a/onchallenge1.htm
>
> The Test harness for the C and C++ dlls was written in Delphi 5. It works ok
> except it kept crashing quite badly when I called a function which passed
> the address of a record in so the called function can access the record
> data. I verified that the record structure size was identical in Delphi and
> the dll.
>
> The call worked fine, but when the delphi function which encapsulates the
> call to the dll function exited, it bombed out. Ie I had done naughty things
> to the stack. The calling convention was stdcall in the Delphi app, the
> default (winapi in Microsoft parlance) in the C/C++ dll which equates to
> stdcall on Windows XP.
>
> I was doing this using loadlibrary btw. Ie select a dll, then use
> GetProcAddress and call it.
>
> type
> TPlayerHistory = packed record // 104 bytes in size- same as in dll
> MoveCount : integer;
> Moves : array[1..100] of char;
> end;
> TmyfuncMove = function(var p : TPlayerHistory):integer;stdcall;
>
> var
> dllhandle : THandle;
> pdllpathname : pchar;
> dllpathname:string;
> s : string;
> fm : TMyFuncMove;
> p : Pchar;
> history : TPlayerHistory;
> This is the function that bombs out.
>
> function GetMove:string;
> var b : byte; // <- fixes the bug, crashes if this unused variable is
> removed!
> begin
> result :='Failed to locate entry point GetMove';
> try
> fm := GetProcAddress(dllhandle,'GetMove');
> except
> fm := nil;
> end;
> if not assigned(fm)then
> exit
> else
> begin
> try
> result := Inttostr(fm(History)); // <- Calls the function here
> except
> on e:exception do
> begin
> ShowMessage(E.Message);
> end;
> end;
> end;
> end; // <- crashes here
>
> It's called like this
>
> procedure TForm1.btnStartClick(Sender: TObject);
> var i : integer;
> begin
> dllhandle := 0;
> try
> pdllpathname := pchar(dllpathname);
> dllhandle := LoadLibrary(pdllpathname);
> fillchar(history.moves,sizeof(history.moves),' ');
> for i:= 1 to 10 do
> begin
> History.MoveCount := i-1;
> if i >1 then
> History.Moves[i-1] := 'R';
> ListBox1.Items.Add('Move '+ Inttostr(i)+' = '+ GetMove);
> end;
> finally
> FreeLibrary( dllhandle );
> end;
> end;
>
> I solved it and I think it is a bug in Delphi 5. If there is no local
> variable declared in GetMove, I don't think it saves the stack correctly (I
> had optimise turned off btw) and so crashes. It also crashes if optimization
> is turned on, I presume because it zaps the local variable as it is unused.
>
> At first I thought it was a calling convention mismatch but I proved that it
> wasn't, by adding two dummy parameters and checking that it could still
> access the History record in the dll.
>
> So am I right that it is a bug or missing something else?
>
> David Bolton
Hi David
try changing
> TPlayerHistory = packed record // 104 bytes in size- same as in dll
> MoveCount : integer;
> Moves : array[1..100] of char;
> end;
into
TPlayerHistory = packed record
MoveCount : Integer;
Moves : array[0..99] of Char;
end;
and ommit the b local variable to see if it works.
BTW, what the C dll does with the Moves field? And how access it?
As a zero terminated C/C++ string?
--
Regards
Theo
------------------------
Theo Bebekis
Thessaloniki, Greece
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