what is the use of pure virtual function in c++ code example
Example 1: pure virtual function in c++
#include <iostream>
#include <string>
//Pure virtual function or inteface allows us to define a function in a base class that doesn't have an implementation or definition in the base class and force sub classes to implement that function
//Pure virtual function is also called an interface in other languages
class Entity {
public:
//virtual std::string GetName() { return "Entity"; }//This is a function that is just virtual .Overriding this function in sub class is optional we can instantiate subcllass without overriding or implementing this function
//Below is an example a Pure Virtual Function
//It is an unimplemented function ant it forces the sub class to implement it and define it
//You will not be able to instantiate sub class without implementing or defining the function in sub class
virtual std::string GetName() = 0;
//the pure virtual function must have virtual written at the beginning and =0 at the end
//This function cannot contain any definition in base class,it is just a declaration
};
class Player :public Entity {
std::string m_name;
public:
Player(const std::string& name)
:m_name(name)
{};
void Print() { std::cout << "This is Sub class" << std::endl; };
std::string GetName()override { return m_name; };//Pure virtual functions is implemented here in this sub class
};
void PrintName(Entity* entity) {
std::cout << entity->GetName() << std::endl;
}
int main()
{
//Entity a;//We can't do this because class Entity contains function that is unimplemented
Player x("Jacob");//This will work because we have implemented or defined the function in this sub class
std::cin.get();
}
Example 2: virtual function in c++
#include <iostream>
#include<string>
//Virtual Functions are functions that allow us to override methods in subclasses
//In this example we have an entity class as a base class and class player inherits from public entity
class Entity {
public:
virtual std::string GetName() { return "Entity"; }//It is a method in base class that we want to modify in sub class Player
void Print() { std::cout << "This is Base class" << std::endl;}//function that is not virtual
};
class Player :public Entity {
std::string m_name;
public:
Player(const std::string& name)
:m_name(name)
{};
void Print() { std::cout << "This is Sub class" << std::endl; };//function that is not virtual
std::string GetName()override { return m_name; };//overriding the function in sub class
};
int main()
{
Entity* e = new Entity();
std::cout << e->GetName() << std::endl;
Player* p = new Player("Jacob");
std::cout << p->GetName() << std::endl;
PrintName(p);// This function calls the GetName method from the Player instance despite it takes an entity instance as a parameter this is because player class is a sub class of Entity and the method is marked virtual it will map with the method in the Player class and call it from there .It outputs => Jacob
//if It was not virtual it would have called The method From Entity Instance and output would be => Entity
Entity* notvirtualentity = new Entity();
Player* notvirtualpalyer = new Player("XX");
notvirtualentity = notvirtualpalyer;
notvirtualentity->Print();//It prints => this is base class if it was virtual function it would call print function from Player Class and print => This is subclass
std::cin.get();
}