Mutable Data Members (C++)

 

For the latest documentation on Visual Studio 2017 RC, see Visual Studio 2017 RC Documentation.

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()  
{  
}  

Keywords

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