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Q238981: HOWTO: Passing Optional Parameters When Calling a Function

Article: Q238981
Product(s): Microsoft C Compiler
Version(s): WINDOWS:97; Win95:7.0; winnt:4.0,5.0,6.0
Operating System(s): 
Keyword(s): kbVCkbfaq
Last Modified: 21-JUN-2001

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The information in this article applies to:

- Microsoft Visual C++, version 4.0 
- Microsoft Visual C++, 32-bit Enterprise Edition, versions 5.0, 6.0 
- Microsoft Visual C++, 32-bit Professional Edition, versions 5.0, 6.0 
- Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
- Microsoft Outlook 98 
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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.

Additional query words:

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Keywords          : kbVC kbfaq
Technology        : kbVCsearch kbVC400 kbOutlookSearch kbOfficeSearch kbAudDeveloper kbOffice97Search kbOutlook98Search kbOffice95Search kbOffice95 kbOffice97 kbZNotKeyword3 kbVC32bitSearch kbVCPE500 kbVCPE600 kbVCEE500 kbVCEE600 kbVCLE600
Version           : WINDOWS:97; Win95:7.0; winnt:4.0,5.0,6.0
Issue type        : kbhowto

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