Pointer to Derived Class in C++

The base class pointer can point to both base class & derived class objects. Although, it cannot change the values present in the derived class. Let us see some code examples for the explanation.

Code:

#include<iostream>
using namespace std;

class Base_Class_Details{
   public:
   int age;
   void setAge(int myage){
      age=myage;
   }
   int getAge(){
      return age;
   }
   string name;
   void setName(string myname){
      name=myname;
   }
   string getName(){
      return name;
   }

   void showDetails(){
      cout<< "The age of the person is: " << age <<"\n";
      cout<< "The name of the person is: " << name <<"\n";
   }
};

int main()
{
   Base_Class_Details* my_pointer_base=new Base_Class_Details();

   my_pointer_base->setAge(20);
   my_pointer_base->setName("Pulkit Govrani");
   my_pointer_base->showDetails();

   return 0;

}

Output:

The age of the person is: 20
The name of the person is: Pulkit Govrani

Code Explanation:

In the above code, we have created a class named as Base_Class_Details. Now we created 2 variables as age, name. Both getter and setter methods are defined for these variables. Then there is a method “showDetails” which is going to print the values of the variables.

It is time to declare a pointer of Base_Class_Details as my_pointer_base along with new keyword inside the main function. Next the setAge & setName methods are called through the pointer to assign values. Lastly we have called the showDetails method to print the details of the person.

Code:

#include<iostream>
using namespace std;

class Base_Class_Details{
   public:
   int age;
   void setAge(int myage){
      age=myage;
   }
   int getAge(){
      return age;
   }
   string name;
   void setName(string myname){
      name=myname;
   }
   string getName(){
      return name;
   }

   void showDetails(){
      cout<< "The age of the person is: " << age <<"\n";
      cout<< "The name of the person is: " << name <<"\n";
   }
};

class Derived_Class_Details: public Base_Class_Details{
   public:
   string profession;
   void setProfession(string prof){
      profession=prof;
   }

   void showDetails(){
      cout<< "The age of the person is: " << age <<"\n";
      cout<< "The name of the person is: " << name <<"\n";
      cout<<"The profession of the person is: "<<profession<<"\n"; 
   }

};

int main()
{
   Base_Class_Details* my_pointer_base=new Base_Class_Details();
   Base_Class_Details base_object;
   Derived_Class_Details derived_object;
   my_pointer_base = &derived_object; // Here our base class pointer is pointing to the derived class

   my_pointer_base->setAge(20);
   my_pointer_base->setName("Pulkit Govrani");
   // my_pointer_base->setProfession("Freelancer"); //This will result into an error.
   my_pointer_base->showDetails();

   Derived_Class_Details * my_pointer_derived;
   my_pointer_derived = &derived_object;
   my_pointer_derived->setAge(21);
   my_pointer_derived->setProfession("Freelancer");
   my_pointer_derived->showDetails();

   return 0;

}

Output:

The age of the person is: 20
The name of the person is: Pulkit Govrani
The age of the person is: 21
The name of the person is: Pulkit Govrani
The profession of the person is: Freelancer

Code Explanation:

In the above code, we have created the same class Base_Class_Details and it contains the same methods as above. Now we have inherited this class onto the class Derived_Class_Details publically.

The Derived_Class_Details class contains an additional function as setProfession which is taking string as an argument.

Let’s move inside the main method, there are two objects created for both Base_Class_Details & Derived_Class_Details classes. The base pointer is pointing to the derived class object. Then we are setting the age, and name of the person through the base pointer.

If you try to access the object from Derived Class then it will throw an error (refer to the commented code where base_pointer is calling the setProfession method.) One more pointer of derived_class is created, followed by setting up the age, and profession of the person. The last showDetails method is called to print the output.

I hope you have understood both of the above programs, feel free to comment below if you are still facing any difficulties.