PRB: Older MFC OCX Controls Incompatible with Visual Basic 4.0

• Microsoft Visual Basic Standard, Professional, and Enterprise Editions, 16-bit and 32-bit, for Windows, version 4.0

SYMPTOMS

Upon placing an OCX control on a Visual Basic form, the control will ASSERT or cause a General Protection Fault. The most common asserts are as follows:

• Assertion Failure in CTLPROP.CPP Line 768
• Assertion Failure in CTLMODUL.CPP Line 128

CAUSE

OLE Custom Controls (OCX Controls) created using the Microsoft Foundation Classes (MFC) that ship with Microsoft Visual C++ version 2.0 or earlier for 32-bit development and Microsoft Visual C++ 1.51 or earlier for 16-bit development will not work properly in Visual Basic 4.0.

The OCX standards and implementations have changed such that some minor incompatibilities have been created. The following MFC code raises the assertion when Visual Basic passes NULL as parameters:

   STDMETHODIMPCOleControl::XPerPropertyBrowsing::GetPredefinedStrings(
       DISPID dispid,
   CALPOLESTR FAR* lpcaStringsOut, CADWORD FAR*
    lpcaCookiesOut)
   {
       ...
       METHOD_MANAGE_STATE(COleControl,PerPropertyBrowsing)
       ...
       ASSERT_POINTER(lpcaStringsOut,CALPOLESTR);
       ASSERT_POINTER(lpcaCookiesOut, CADWORD);
       ...
   }

RESOLUTION

Upgrade to Visual C++ 2.1 or higher for 32-bit development and Visual C++ 1.52 or higher for 16-bit development.

STATUS

Microsoft has confirmed this to be a problem with Visual C++ version 2.0 and earlier for 32-bit development and Visual C++ 1.51 and earlier for 16-bit development.