Delphi DLL called from C++ crashes when showing a form -

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edit: dumb question, fixed. form1 nil because didn't assign new tform1, forgot delphi doesn't c++.

i have delphi dll want use gui of c++ program, starters, created form, , have function show form exported c++ can call it. however, program crashes when calls function. here code. (i using delphi 2010)

the delphi part:

unit main;  interface  uses   windows, messages, sysutils, variants, classes, graphics, controls, forms,   dialogs, tabs, comctrls;  type   tform1 = class(tform)     tabcontrol1: ttabcontrol;     tabset1: ttabset;   private     { private declarations }   public     { public declarations }   end;  var   form1: tform1;  function showform(i: integer) : integer; export; cdecl;  exports   showform name 'showform';  implementation  {$r *.dfm}  function showform(i: integer) : integer; export; cdecl; begin   form1.show();    result := 3; // random value, doesn't mean end;  end.

and here c++ code:

hmodule h = loadlibrary("delphidll.dll");  if (!h) {     printf("failed loadlibrary (getlasterror: %i)\n", getlasterror());      return 0; }  farproc p = getprocaddress(h, "showform");  if (p)     printf("found @ %p\n", p); else     printf("didn't find it\n");  ((int(__cdecl *)(int))p)(34);  system("pause");  return 0;

the program prints "found @ " , crashes. if comment out form1.show() in delphi dll, doesn't crash, , function returns 3 (tested printf). missing initialization or something? thanks.

the reason crases var form1: tform1; not initialized.

the reason var form1: tform1; not initialized, because put unit main dll project, came delphi vcl project had form1 on auto-creation list.

the auto-creation list means delphi .dpr initialize form.

now need manually create form, need export these 3 new routines dll, , have c++ dll call them:

function createform() : integer; export; cdecl; begin   try     application.createform(tform1, form1);     result := 0;   except     result := -1;   end; end;  function destroyform() : integer; export; cdecl; begin   try     if assigned(form1)     begin       freeandnil(form1);       application.processmessages();     end;     result := 0;   except     result := -1;   end; end;  function destroyapplication() : integer; export; cdecl; begin   try     freeandnil(application);     result := 0;   except     result := -1;   end; end;

in addition, should put try...except block around implementation of showform function implementation, exceptions , other language dependent run-time features should not cross dll boundaries.

you should similar things releasing other potentially allocated pieces of dynamic memory too.

--jeroen


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