Calling base class' constructor without defining it in derived class

Question

class A {
public:
  int _a
  A(int a) : _a { a} { }
};

class B : public A { }

Why can't I initialize a variable of A type with using the inherited constructor?

B a(5);

Error: "No matching constructor for initialization of 'B'"

Remember to specify a virtual desctructor or a protected non-virtual one. — Fantastic Mr Fox, Sep 14 '21 at 07:16

score 3 · Accepted Answer · answered Sep 14 '21 at 07:10

3

Because B doesn't have such a constructor taking int by default, unless inherit it explicitly:

class B : public A { 
    using A::A; // inheriting constructor
};

answered Sep 14 '21 at 07:10

songyuanyao

is there a way to make this implicit, so that any subclasses of a class will always inherit the base class' constructor without using the `using` directive? – luis Sep 14 '21 at 07:21
2

@luis AFAIK, no. – songyuanyao Sep 14 '21 at 07:24

1 Answers1