optional-cpp.md

description	title	ms.date	f1_keywords	helpviewer_keywords	ms.assetid
Learn more about: optional (C++)	optional (C++ COM Attribute)	10/02/2018	vc-attr.optional	optional attribute	86656a66-8e11-4589-8e30-9b0f34eeed03

optional (C++)

Specifies an optional parameter for a member function.

Syntax

[optional]

Remarks

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

Example

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);
};

Requirements

Attribute context	Value
Applies to	Interface parameter
Repeatable	No
Required attributes	None
Invalid attributes	None

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

See also

IDL Attributes
Parameter Attributes