Pointer to a callback in a DLL

I'm calling a Dialog that has it's resources and dlg-procedure in a DLL. I'm not using a DEF file or LIB file. The function names are known, the function args are known, I'm using GetProcAddress to get a pointer to the functions I'm interested in.

'Why' I'm doing it this way is of no consequence, it's an experiment in 'learning'.

This works on _cdecl functions, but on the CALLBACK (_stdcall), I can't get a pointer to the actual dialog procedure (it returns 0).

Here's how I'm doing my pointers:

//////////////////// DLL TEST STUFF ////////////////////////////

#define   DLLPATH "../../testdll/release/testdll.dll"

//typedef some function pointers
typedef HINSTANCE        (__cdecl *INSTPROC )(void); 
typedef int              (__cdecl *VOIDPROC )(void); 
typedef LRESULT          (__stdcall *DLGROC )(HWND, UINT, WPARAM, LPARAM );

///////////////////////////////////////////////////////////////

As I said, any function that is NOT a callback returns a valid result, additionally, the dialog pops up as expected, no problems with DLL's HINSTANCE.

But without a pointer to it's dlgproc, no button messages have anywhere to go.

Here's some more test code:

 //use DLL funcs without lib or def files

                              //this works
  GetInst = (INSTPROC)GetProcAddress(Loadme,"getinst");
                              //this works
  GetID   = (VOIDPROC)GetProcAddress(Loadme,"getid");
                              //this doesn't work, rets 0
  DlgProc = (DLGPROC) GetProcAddress(Loadme,"dllProc");

  //test for result
  dllid  =(GetID)();
  dllinst=(GetInst)();

  //compare hinst            OK
  wsprintf(buf,"dllinst=%x  Loadme=%x",dllinst, Loadme);
  MessageBox(hwnd,buf,"",MB_OK);

  //check resOurce ID        OK
  wsprintf(buf,"GetID returned: %d",dllid);
  MessageBox(hwnd,buf,"",MB_OK);

  //check dllProc addr       NOGO, ret=0
  wsprintf(buf,"dllProc=%x",DlgProc);
  MessageBox(hwnd,buf,"",MB_OK);

        //    DLL instance,        resource ID,     parent,  dlgproc    
        DialogBox(Loadme  ,  MAKEINTRESOURCE(dllid),  hwnd,  DlgProc);

  //dialog loads and shows, can't get dlgproc addr 

        FreeLibrary(Loadme);
        ///////////////// END DLL TEST STUFF ///////////////

On the DLL side of things, it looks like this:

__declspec(dllexport) LRESULT CALLBACK dllProc(
                                            HWND hwnd, 
              UINT Message, 
              WPARAM wParam, 
              LPARAM lParam
              )
{

hpwnd=hwnd;

 switch (Message){

  case WM_INITDIALOG:
   MessageBox(hwnd,"At DlgProc...","",MB_OK);
  return TRUE;

  case WM_COMMAND:
   switch(LOWORD(wParam)){
       case IDEND:
    case IDCANEND:
      EndDialog(hwnd,0);
   return TRUE;
    }
 return TRUE;
 }
return FALSE;
}

Which really doesn't matter at this point, since I can't get a pointer to the callback in the first place.

If anyone happens to know the fix for getting a pointe开发者_开发百科r to the callback, I would very much appreciate your input.

Thanks for your patience.

You need to declare your dllProc inside an extern "C" block to prevent its name being decorated when exported, so that when you ask for a function called "dllProc" such a function is found (instead of "dllProc@blahmoocow" or whatever madness the C++ decoration produces. :-)).

Place this declaration before the dllProc definition:

extern "C"
{
    __declspec(dllexport) LRESULT CALLBACK dllProc(
           HWND hwnd, UINT Message, WPARAM wParam, PARAM lParam);
}

You can also then drop the __declspec(dllexport) from the dllProc definition.