SAMPLE: OPTARG: Optional parameters with Automation

 Last reviewed: June 5, 1996
Article ID: Q131052
The information in this article applies to:
  • Microsoft OLE Libraries for Windows and Win32s, version 2.03
  • Microsoft OLE libraries included with: 

        - Microsoft Windows NT version 3.5
    - Microsoft Windows 95

SUMMARY

OPTARG is an OLE Automation server application that demonstrates automation methods with optional parameters and variable number of parameters. It implements an Add method that takes optional parameters and a Multiply method that takes a variable number of parameters.

See the README.TXT included with the sample for details to compile and run. 

You can find OPTARG.EXE (size: 35703 bytes) 
                       , a self-extracting file, on these services:
  • Microsoft's World Wide Web site on the Internet 

          On the www.microsoft.com home page, click the Support icon
      Click Knowledge Base, and select the product

          Enter kbfile OPTARG.EXE (size: 35703 bytes) 
                             , and click GO!
      Open the article, and click the button to download the file


  • Internet (anonymous FTP)

          ftp ftp.microsoft.com
      Change to the Softlib/Mslfiles folder
      Get OPTARG.EXE (size: 35703 bytes) 

    

  • The Microsoft Network

          On the Edit menu, click Go To, and then click Other Location
      Type "mssupport" (without the quotation marks)
      Double-click the MS Software Library icon
      Find the appropriate product area
      Locate and Download OPTARG.EXE

    

  • Microsoft Download Service (MSDL)

          Dial (206) 936-6735 to connect to MSDL
      Download OPTARG.EXE (size: 35703 bytes) 

    
For additional information about downloading, please see the following
article in the Microsoft Knowledge Base:

    

       ARTICLE-ID: Q119591
   TITLE     : How to Obtain Microsoft Support Files from Online Services


    MORE INFORMATION
    
 

    
Optional parameters are implemented by marking the parameter with the
optional attribute and by using VARIANT as the type of the parameter. If
the controller omits a parameter, the method will be passed a VARIANT
with VARIANT.vt = VT_ERROR and VARIANT.scode = DISP_E_PARAMNOTFOUND.

    
Variable parameters are implemented by marking the method with the
vararg attribute and by providing a parameter of type SAFEARRAY(variant).
This array will contain the variable number of parameters passed by the
controller.

    
Note that vararg methods do not have the upper limit of parameters that
methods with optional parameters do.

    
Because of a problem in the OLE dlls, invoking the Multiply method will
cause an exception in the 32-bit OLE that shipped with Windows NT 3.5 and a
GP fault in 16-bit OLE 2.02 and 2.03. This problem has been fixed in
NT 3.51 and Windows 95.

    
The problem occurs if a vararg method has a retval parameter. For
example, the following will fail:

    

            [vararg]
        HRESULT Multiply([in] short RequiredInteger,
                      [in] SAFEARRAY(variant) VariableNumberOfIntegers,
                      [out, retval] long* retval);


    The problem does not occur if the vararg method doesn't have a retval
parameter. For example, the following will currently work:

    

            [vararg]
        HRESULT Multiply([in] short RequiredInteger,
                      [in] SAFEARRAY(variant) VariableNumberOfIntegers);

        [vararg]
       long Multiply([in] short RequiredInteger,
                      [in] SAFEARRAY(variant) VariableNumberOfIntegers);

    

	    
	
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Additional reference words: arguments 3.50 4.00
    
KBCategory: kbfile
    
KBSubcategory: LeTwoAt
    

    
    

    

    
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	Last reviewed:  June 5, 1996
	
    
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