Answers for "abstract class in c++"

what is abstract class in c++

when we use abstract classes? supposably we have class Car. 
you don't want to use it directly. you need extend this class. 
thats why you must declare this class as abstract. 
then you only can extend this class with all methods.

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();
}

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();
}

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;
}

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)
}

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.
}