c++ two versions of overloading subscript operator

Question

My question is about the difference between:

const T& operator[](const int nIndex) const;

and:

T& operator[](const          


        

Answer 1

Those are member functions of a class, and the version will be chosen based on whether that class in used as a const context.

This version will be called when [] is used on a object in a const context. It preserves the const-ness of the returned element.

const T& operator[](const int nIndex) const;

This version will be called when [] is used on a non-const object. It specifies that when your object isn't const, you'll get an element that you can modify, allowing code like myObject[0] = 10;

T& operator[](const int nIndex);