const_cast VS mutable ? any difference?

Question

From my understanding , mutable cancels the constness of a variable

Class A {
  void foo() const {
  m_a = 5;
}
mutable int m_a;
};
         


        

Answer 1

Simply put, declaring a member variable as mutable makes it write-accessible from any constant method of that class without any other special syntax. const_cast on the other hand has to be performed whenever you want write access to an otherwise constant variable, and that variable doesn't even have to be a class member.

Unless you want to explicitly allow write access to a member variable, using const_cast in every case of violation of const correctness is preferred, if only to clearly state your intentions.

On a side note, const_cast can also be used to add or remove the volatile modifier.