optional (C++)

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Specifies an optional parameter for a member function.

  
[optional]  
  

The optional C++ attribute has the same functionality as the optional MIDL attribute.

The following code shows how optional might be used:

// cpp_attr_ref_optional.cpp  
// compile with: /LD  
#include "unknwn.h"  
[module(name="ATLFIRELib")];  
  
[dispinterface, uuid("00000000-0000-0000-0000-000000000001")]  
__interface IFireTabCtrl : IDispatch  
{  
   [id(1)] long procedure ([in, optional] VARIANT i);  
};  

Attribute Context

For more information about the attribute contexts, see Attribute Contexts.

IDL Attributes
Parameter Attributes
Attributes Samples