C++ Copy Constructor, Assignment Operator

Copy Constructor

Song(Song const&);

It is needed if you want to initialize an object to take the value of another one:

Song a;
Song b = a;    // Calls copy constructor

Assignment Operator

void operator=(const Song&);

It is needed for assigning a value to an already existing instance:

Song a;
Song b;
b = a;        // Calls assignment operator

Note that the standard return value for an assignment operator is a reference:

Song& operator=(const Song&);