what does "const" mean when overloading operator in C++ [duplicate]

Question

I saw something like:

const char& operator[] (int Index) const

the first const I understand. It's to protect the returning char from being modified.

But what does second const mean? Why do we sometimes use two const, sometimes just one?

Answer 1

It can be used for any member function, not only operators. It means, that this function will:

• not be able to modify any data members (except mutable ones)
• will not be able to call any non-const member functions