How to pass optional parameters when you call a function in Visual C++ (238981)

The information in this article applies to:

Microsoft Visual C++ 4.0
Microsoft Visual C++, 32-bit Enterprise Edition 5.0
Microsoft Visual C++, 32-bit Enterprise Edition 6.0
Microsoft Visual C++, 32-bit Professional Edition 5.0
Microsoft Visual C++, 32-bit Professional Edition 6.0
Microsoft Visual C++, 32-bit Learning Edition 6.0

This article was previously published under Q238981

SUMMARY

When you call a method that has optional parameters from Visual C++, you cannot omit the optional parameters. You need to pass a special VARIANT instead.

MORE INFORMATION

Some methods have "optional" parameters. In Visual Basic, you can omit them when calling the method. However, when calling with Visual C++, you have to pass a special VARIANT whose .vt field has the value VT_ERROR and .scode field has the value DISP_E_PARAMNOTFOUND. That is:

      // VARIANT used in place of optional-parameters.
      VARIANT varOpt;
      varOpt.vt = VT_ERROR;
      varOpt.scode = DISP_E_PARAMNOTFOUND;

This is what Visual Basic is doing behind-the-scenes.

Modification Type:	Major	Last Reviewed:	9/1/2005
Keywords:	kbhowto KB238981 kbAudDeveloper