inheriting constructor c++

inheriting constructor

As the name suggested that we can inherit the base class constructor in derive class and we can use them.

How to use inheriting constructor:

//In Derive class, use the "using" keyword like below
using baseClassName::baseClassName; //inheriting constructor

Important points:

• We should use the inheriting constructor in derived class which has no data members.
• If derived class has own data members and we are using inheriting constructor then use “in class member initialization” for own data members.
• If we are using inheriting constructor and writes own constructors of derived class then these derived class constructors will overwrite inheriting constructors.
• When we use inheriting constructor then compiler generated the same copy of base class constructors in derived class.

source code with example:

/*
Program:Inheritance Constructor 
Author: Alpha Master
Date: 12 March 2021
*/

//Header File
#include<iostream>

class base
{
    int m_a;
public:
     base()
     {
         m_a = 0;
         std::cout<<"default base constructor"<<std::endl;
     }    

     base(int tmp)
     {
         m_a = tmp;
         std::cout<<"parameterized base constructor"<<std::endl;
     }

     base(const base& tmpObj)
     {
         m_a = tmpObj.m_a;
         std::cout<<"copy base constructor"<<std::endl;
     }

    ~base()
     {
         m_a = 0;
         std::cout<<"base destructor"<<std::endl;
     }
     void print()
     {
         std::cout<<"A:"<<m_a<<std::endl;
     }

};

class derived: base
{
    int m_b{5}; //in class member initialization
    using base::base;  //inheriting constructor
public:
    void print()
    {
        std::cout<<"B:"<<m_b<<std::endl;
    }
};

int main()
{
    std::cout<<"Inheritance Constructor"<<std::endl;
    base obj(10);
    obj.print();
    derived obj2;
    obj2.print();
    return 0;
}

Output:

Inheritance Constructor
parameterized base constructor
A:10
default base constructor
B:5
base destructor
base destructor

Conclusion: I would suggest not to use this feature and restrict the use of inheriting constructor to a class which has no data members.