Base class pointer pointing to derived class object

Pointer is a data type that stores the address of other data types.

The pointer of Base Class pointing different object of derived class:

Approach:

• A derived class is a class which takes some properties from its base class.
• It is true that a pointer of one class can point to other class, but classes must be a base and derived class, then it is possible.
• To access the variable of the base class, base class pointer will be used.
• So, a pointer is type of base class, and it can access all, public function and variables of base class since pointer is of base class, this is known as binding pointer.
• In this pointer base class is owned by base class but points to derived class object.
• Same works with derived class pointer, values is changed.

Below is the C++ program to illustrate the implementation of the base class pointer pointing to the derived class:

C++

// C++ program to illustrate the
// implementation of the base class
// pointer pointing to derived class
#include <iostream>
using namespace std;

// Base Class
class BaseClass {
public:
    int var_base;

    // Function to display the base
    // class members
    void display()
    {
        cout << "Displaying Base class"
             << " variable var_base: " << var_base << endl;
    }
};

// Class derived from the Base Class
class DerivedClass : public BaseClass {
public:
    int var_derived;

    // Function to display the base
    // and derived class members
    void display()
    {
        cout << "Displaying Base class"
             << "variable var_base: " << var_base << endl;
        cout << "Displaying Derived "
             << " class variable var_derived: "
             << var_derived << endl;
    }
};

// Driver Code
int main()
{
    // Pointer to base class
    BaseClass* base_class_pointer;
    BaseClass obj_base;
    DerivedClass obj_derived;

    // Pointing to derived class
    base_class_pointer = &obj_derived;

    base_class_pointer->var_base = 34;

      // If you uncomment this line of code this will cause the following error
      // As base-class pointer cannot access the derived class variable.
      //base_class_pointer->var_derived = 98;
      //output: error: ‘class BaseClass’ has no member named ‘var_derived’

      // Calling base class member function
    base_class_pointer->display();

    base_class_pointer->var_base = 3400;
    base_class_pointer->display();

    DerivedClass* derived_class_pointer;
    derived_class_pointer = &obj_derived;
    derived_class_pointer->var_base = 9448;
    derived_class_pointer->var_derived = 98;
    derived_class_pointer->display();



    return 0;
}

Output

Displaying Base class variable var_base: 34
Displaying Base class variable var_base: 3400
Displaying Base classvariable var_base: 9448
Displaying Derived  class variable var_derived: 98

Output:

Displaying Base class variable var_base: 34
Displaying Base class variable var_base: 3400
Displaying Base classvariable var_base: 9448
Displaying Derived  class variable var_derived: 98

Conclusion:

• A pointer to derived class is a pointer of base class pointing to derived class, but it will hold its aspect.
• This pointer of base class will be able to temper functions and variables of its own class and can still point to derived class object.