C++ Abstract Class: constructor yes or no?

Question

A class with one (or more) virtual pure functions is abstract, and it can\'t be used to create a new object, so it doesn\'t have a constructor.

I\'m reading a book t

Answer 1

If The base abstract class does not have a constructor, how would you assign values to firstname , lastname members for any derived class, when you are creating an object of the derived class?

Suppose there is a Manager Class derived from Employee which adds Salary data and implements earning(). Now Employee is an abstract class but Manager is a concrete class and hence you can have an object of Manager. But when you are instantialting Manager, you need to initialize/assign values to members inherited from base class i.e. Employee. One way is that you can have setFirstName() & setLastName() in the base class for this purpose and you can use them in the constructor for derived class i.e. Manager or more convenient way would be to have a constructor in your base abstract class Employee.

See the code below:

#include 
#include 
#include 

using namespace std;


class Employee {
   public:
       Employee(const char*, const char*);
       ~Employee();
       const char* getFirstName() const;
       const char* getLastName() const;


       virtual double earnings() const=0;  // pure virtual => abstract class
       virtual void print() const;

  private:
       char* firstname;
       char* lastname;
};

Employee::Employee(const char* first, const char* last){
firstname= (char*) malloc((strlen(first)+1)*sizeof(char));
lastname= (char*) malloc((strlen(last)+1)*sizeof(char));
strcpy(firstname,first);
strcpy(lastname,last);
}

Employee::~Employee(){
free(firstname);
free(lastname);
cout << "Employee destructed" << endl;
}

const char* Employee::getFirstName() const{ return firstname;}
const char* Employee::getLastName() const{ return lastname; }
void Employee::print() const{
      cout << "Name: " << getFirstName() << " " << getLastName() << endl;
      }



class Manager:public Employee{
   public:
      Manager(char* firstname,char* lastname,double salary):
    Employee(firstname,lastname),salary(salary){}

      ~Manager(){}

      double earnings() const {return salary;}

   private:
      double salary;          
};

int main(){

Manager Object("Andrew","Thomas",23000);    
Object.print();
cout << " has Salary : " << Object.earnings() << endl;

    return 0;
}