const before parameter vs const after function name c++

Question

What is the difference betweeen something like this

friend Circle copy(const Circle &);

and something like this

friend          


        

Answer 1

Circle copy(Circle&) const;

makes the function const itself. This can only be used for member functions of a class/struct.

Making a member function const means that

• it cannot call any non-const member functions
• it cannot change any member variables.
• it can be called by a const object(const objects can only call const functions). Non-const objects can also call a const function.
• It must be member function of the class 'Circle'.

Now consider the next one:

Circle copy(const Circle &);

while this one means that the parameter passed cannot be changed within the function. It may or may not be a member function of the class.

NOTE: It is possible to overload a function in such a way to have a const and non-const version of the same function.