Calling the DLL Function

Once you have obtained the address of the target DLL function, you can call it from APP16 using the CallProcEx32W or CallProc32W function. You cannot create a prototype for CallProc32W unless you do one of the following:

Restrict each file so that it only uses calls to functions that contain the same number of parameters.
Create a prototype CallProc32W_1 for functions that use one parameter, CallProc32W_2 for functions that use two parameters, and so forth. When linking your application or DLL, use forwarders to map calls to these functions to CallProc32W.

This is a limitation of the Pascal calling convention. For this reason, you may choose to use the CallProcEx32W function, which uses the C calling convention to support a variable number of arguments.

These examples call MyPrint, passing two arguments, a string and a window handle. All parameters must be 32-bit values. Therefore, the string is declared using a FAR pointer, as shown here:

char FAR *TestString = "Hello there";

You must convert the 16-bit window handle to a 32-bit window handle using the WOWHandle32 function, as shown here:

// Convert the window handle.
DWORD hWnd32;
hWnd32 = WOWHandle32(hWnd, WOW_TYPE_HWND);

This first example uses CallProcEx32W.

// Call the MyPrint routine in the Win32-based DLL
CallProcEx32W( 2 | CPEX_DEST_STDCALL, 
                                   2, 
                               hProc, 
                  (DWORD) TestString, 
                              hWnd32);

This next example uses CallProc32W:

// Call the MyPrint routine in the Win32-based DLL
CallProc32W( (DWORD) TestString, 
                         hWnd32, 
                          hProc, 
                              2, 
          2 | CPEX_DEST_STDCALL);

A mask of 2 (0x10) is given because we want to pass TestString by reference and hProc by value. The system translates the pointer for us.

If you are isolating your thunking code into DLL16, put the call to CallProc32W or CallProcEx32W in the MyPrint function of the DLL16 code.