CODEWITHSUNDEEP
c++oopconstructor
CodeCrusader
CodeCrusader

Reputation: 579

Pass Parameter to Base Class Constructor while creating Derived class Object

Consider two classes A and B

class A
{
public:
    A(int);
    ~A();
};

class B : public A
{
public:
    B(int);
    ~B();
};


int main()
{
    A* aobj;
    B* bobj = new B(5);    
}

Now the class B inherits from A.

I want to create an object of B. I am aware that creating a derived class object, will also invoke the base class constructor , but that is the default constructor without any parameters.

What i want is that B to take a parameter (say 5), and pass it on to the constructor of A. Please show some code to demonstrate this concept.

Upvotes: 37

Views: 76919

Answers (4)

Wilson
Wilson

Reputation: 151

class A { public: int aval;

A(int a):aval(a){};
~A();

};

class B : public A { public: int bval;

B(int a,int b):bval(a),A(b){};
~B();

};

int main() {

  B *bobj = new bobj(5,6);
//or 
  A *aobj=new bobj(5,6);

}

In this case you are assigning the values for base class and derived class .

Upvotes: 0

Mandeep Singh
Mandeep Singh

Reputation: 365

If you are using your derived class constructor just to pass arguments to base class then you can also do it in a shorter way in C++11:

class B : public A
{
    using A::A;
};

Note that I have not even used "public" access specifier before it. This is not required since inherited constructors are implicitly declared with same access level as in the base class.

For more details, please refer to section Inheriting constructors at: https://en.cppreference.com/w/cpp/language/using_declaration

Also you may refer to https://softwareengineering.stackexchange.com/a/307648 to understand limitations on constructor inheritance.

Upvotes: 10

Bathsheba
Bathsheba

Reputation: 234665

Use base member initialisation:

class B : public A
{
public:
    B(int a) : A(a)
    {
    }
    ~B();
};

Upvotes: 54

SomeWittyUsername
SomeWittyUsername

Reputation: 18348

B::B(int x):A(x)
{
    //Body of B constructor
}

Upvotes: 15

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