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• Upcasting is the process of creating the derived class’s pointer or reference from the base class’s pointer or reference.
• It refers to the process of converting a derived class’s reference or pointer to a base class’s reference or pointer.
• Upcasting is a safer casting technique than downcasting.
• It supports public inheritance, which allows references to be implicitly cast from one class to another without an explicit typecast.
• Upcasting by default creates an is-a relationship between the base and derived classes.

For instance,

#include <iostream>
using namespace std;

// This is Parent class
class Base
{
  public:
    void print()
    {
      cout << "Parent Class print function" << endl;
    }
};

// This is Child class
class Subclass : public Base
{
  public:
  void print()
  {
    cout << "Child Class print function" << endl; 
  } 
};

int main() 
{ 
  Base *base_object; 
  Subclass sub_object; 
  base_object = &sub_object; 

  // also as we are dealing with pointers instead of . we need to use ->
  base_object->print();

  return 0;
}

Output:

Parent Class print function

Downcasting is the inverse of Upcasting, in which we convert a reference or pointer from a Super class to a reference or pointer from a derived class. We’ll learn more about Downcasting later.

Functions that are never Inherited:

• Constructors and Destructors are not inherited and thus cannot be overridden.
• Additionally, the assignment operator ‘=’ is never inherited. It is overloaded but not inheritable by subclasses.

Static member functions and inheritance:

Static member functions behave similarly to non-static member functions:

• They inherit into the derived class.
• When we redefine a static member, all the base class’s overloaded functions are hidden.
• If the signature of a function in the base class is changed, all base class versions with that function name are hidden (this is a variation of the previous point).

Note: also read about Order of Constructor Call in C++

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