readonly-cpp.md

title	readonly (C++ COM Attribute) | Microsoft Docs
ms.custom
ms.date	10/02/2018
ms.technology	cpp-windows
ms.topic	reference
f1_keywords	vc-attr.readonly
dev_langs	C++
helpviewer_keywords	readonly attribute
ms.assetid	1246cadd-5304-43a9-beea-51153d12704d
author	mikeblome
ms.author	mblome
ms.workload	cplusplus uwp

readonly (C++)

Prohibits assignment to a data member.

Syntax

[readonly]

Remarks

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

If you want to prohibit modification of a method parameter, then use the in attribute.

Example

The following code shows a use of the readonly attribute:

// cpp_attr_ref_readonly.cpp
// compile with: /LD
[idl_quote("midl_pragma warning(disable:2461)")];
#include "unknwn.h"
[module(name="ATLFIRELib")];

[dispinterface, uuid(11111111-1111-1111-1111-111111111111)]
__interface IFireTabCtrl
{
   [readonly, id(1)] int i();
};

Requirements

Attribute Context

Applies to	Interface method
Repeatable	No
Required attributes	None
Invalid attributes	None

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

See Also

IDL Attributes
Data Member Attributes