Using base default constructor (with parameters) for child class

问题

I have a class A which has to have a a class passed to it; From A I have two classes B and C; is it possible for B and C to use the constructor from A, as apposed to the default constructor.

     A
    / \
   B   C 

A::A(randomNumber &rnd)
{
    ....
}

回答1:

Yes, it is possible:

class B
{
public:
    B(randomNumber& rnd) : A(rnd) { }
    // ...
};

If you want to call A's constructor in B's default constructor, you will have to pass a global object: since A's construct accepts an lvalue reference, creating a temporary is not an option.

B() : A(global_random_number);

回答2:

Yes. Use

class B {
public:
   B() : A(someRndNum) {}
};

and same for C.

回答3:

You can use following syntax:

B::B() : A(aRandomNum)
{
    ....
}

来源：https://stackoverflow.com/questions/15569020/using-base-default-constructor-with-parameters-for-child-class