C ++继承了复制构造函数调用？

Question

I have class B derived from class A. I call copy constructor that I implemented myself for an object of class B. I also implemented myself a constructor for class A.

Is this copy constructor automatically called when I call copy constructor for class B ? Or how to do this ? Is this the good way:

A::A(A* a)
{
    B(a);
    // copy stuff
}

thanks!

Answer 1

You can do this with a constructor initialization list, which would look like this:

B::B(const B& b) : A(b)
{
    // copy stuff
}

I modified the syntax quite a bit because your code was not showing a copy constructor and it did not agree with your description.

Do not forget that if you implement the copy constructor yourself you should follow the rule of three .

Answer 2

A copy constructor has the signature:

A(const A& other)  //preferred 

or

A(A& other)

Yours is a conversion constructor. That aside, you need to explicitly call the copy constructor of a base class, otherwise the default one will be called:

B(const B& other) { }

is equivalent to

B(const B& other) : A() { }

ie your copy constructor from class A won't be automatically called. You need:

B(const B& other) : A(other) { }