abstract classes c++ code example

Example 1: interfaces 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
};

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: what is abstract class in c++

//Code by Soumyadeep Ghosh 
//insta : @soumyadepp
//linked in : https://www.linkedin.com/in/soumyadeep-ghosh-90a1951b6/
#include <bits/stdc++.h>

using namespace std;

class person
{
  string p_id;
  public:
  virtual void get_info()=0; //declaring person as abstract class
  virtual void show()=0;
};

class student:public person
{
  string name;
  int roll_no;
  public:
  /*overriding the pure virtual function declared in base class otherwise
    this class will become an abstract one and then objects cannot be created
    for the same*/
    void get_info()
    {
      cout<<"Enter name of the student "<<endl;
      cin>>name;
      cout<<"Enter roll number of the student "<<endl;
      cin>>roll_no;
    }
   void show()
   {
     cout<<"Name : "<<name<<" Roll number: "<<roll_no<<endl;
   }
};

int main()
{
  person *p;
  p=new student;
  p->get_info();
  p->show();
  return 0;
}

Example 3: abstract class in c++

struct Abstract {
    virtual void f() = 0; // pure virtual
}; // "Abstract" is abstract
 
struct Concrete : Abstract {
    void f() override {} // non-pure virtual
    virtual void g();     // non-pure virtual
}; // "Concrete" is non-abstract
 
struct Abstract2 : Concrete {
    void g() override = 0; // pure virtual overrider
}; // "Abstract2" is abstract
 
int main()
{
    // Abstract a; // Error: abstract class
    Concrete b; // OK
    Abstract& a = b; // OK to reference abstract base
    a.f(); // virtual dispatch to Concrete::f()
    // Abstract2 a2; // Error: abstract class (final overrider of g() is pure)
}

Example 4: cpp make class abstract

struct Abstract
{
     virtual ~Abstract() = 0;
};

Abstract::~Abstract() {}

struct Valid: public Abstract
{
        // Notice you don't need to actually overide the base
        // classes pure virtual method as it has a default
};


int main()
{
    // Abstract        a;  // This line fails to compile as Abstract is abstract
    Valid           v;  // This compiles fine.
}