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---
title: "Mutable Data Members (C++) | Microsoft Docs"
ms.custom: ""
ms.date: "11/04/2016"
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ms.technology: ["cpp-language"]
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ms.topic: "language-reference"
f1_keywords: ["mutable_cpp", "mutable"]
dev_langs: ["C++"]
helpviewer_keywords: ["[""mutable keyword [C++]""]"]
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author: "mikeblome"
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---This keyword can only be applied to non-static and non-const data members of a class. If a data member is declared mutable, then it is legal to assign a value to this data member from a const member function.
mutable member-variable-declaration;
For example, the following code will compile without error because m_accessCount has been declared to be mutable, and therefore can be modified by GetFlag even though GetFlag is a const member function.
// mutable.cpp
class X
{
public:
bool GetFlag() const
{
m_accessCount++;
return m_flag;
}
private:
bool m_flag;
mutable int m_accessCount;
};
int main()
{
}