How to clone object in C++ ? Or Is there another solution?

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The typical solution to this is to write your own function to clone an object. If you are able to provide copy constructors and copy assignement operators, this may be as far as you need to go.

class Foo
{ 
public:
  Foo();
  Foo(const Foo& rhs) { /* copy construction from rhs*/ }
  Foo& operator=(const Foo& rhs) {};
};

// ...

Foo orig;
Foo copy = orig;  // clones orig if implemented correctly

Sometimes it is beneficial to provide an explicit clone() method, especially for polymorphic classes.

class Interface
{
public:
  virtual Interface* clone() const = 0;
};

class Foo : public Interface
{
public:
  Interface* clone() const { return new Foo(*this); }
};

class Bar : public Interface
{
public:
  Interface* clone() const { return new Bar(*this); }
};


Interface* my_foo = /* somehow construct either a Foo or a Bar */;
Interface* copy = my_foo->clone();

EDIT: Since Stack has no member variables, there’s nothing to do in the copy constructor or copy assignment operator to initialize Stack‘s members from the so-called “right hand side” (rhs). However, you still need to ensure that any base classes are given the opportunity to initialize their members.

You do this by calling the base class:

Stack(const Stack& rhs) 
: List(rhs)  // calls copy ctor of List class
{
}

Stack& operator=(const Stack& rhs) 
{
  List::operator=(rhs);
  return * this;
};

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