How to Properly Initialize Base Class Member Variables in a Derived Class Constructor?

Initialization of Base Class Member Variables in Derived Class Constructor

When working with class inheritance, a common question arises: how to initialize base class member variables within a derived class constructor. An initial attempt to do so may lead to confusion, as demonstrated below:

class A {
public:
    int a, b;
};

class B : public A {
    B() : A(), a(0), b(0) {
    }
};

This code fails to compile, raising the question: why can't we initialize a and b in B?

The reason lies in the fact that a and b are not members of B. They belong to the base class A. Only A can initialize its own member variables.

One possible solution is to make a and b public members of A, allowing B to assign values directly. However, this is not recommended as it breaks the encapsulation principle.

Instead, a more robust approach is to define a constructor in A that allows derived classes to specify initialization values. This can be achieved by making the constructor protected and accessible to subclasses:

class A {
protected:
    A(int a, int b) : a(a), b(b) {} // Accessible to derived classes
private:
    int a, b; // Keep variables private within A
};

class B : public A {
public:
    B() : A(0, 0) // Calls A's constructor, setting a and b to 0 within A
    {
    }
};

This solution ensures that a and b are initialized correctly within A, guaranteeing data integrity and encapsulation.

The above is the detailed content of How to Properly Initialize Base Class Member Variables in a Derived Class Constructor?. For more information, please follow other related articles on the PHP Chinese website!