How to call an object constructor inside another constructor?

Question

I have an abstract class A and a class B with the constructor:

B(A &a) {...}

Now, I create these objects in the main program as follow:

int main(){
  std::unique_ptr<A> a = make_A();//don't mind make_A()
  if(a==null)
    a = make_default_A();
  B b (*a); 
}

Now I created a class which setups the system:

class System{
public:
  System();
private:
  B b;
  std::unique_ptr<A> a;
}

And the constructor is:

System(){
  a = make_A();
  if(a==null)
    a = make_default_A();
  b(*a);
}

Obviously this is wrong because I can't call B's constructor as in the code above, but I can't figure out how to do this. The only solution that came to my mind is to use std::unique_ptr<B> b; instead of B b; and then call b = make<B> (*a);.

`b = B(*a);`should re-initialized `b` (note that its first initialization happens before the constructor is entered) — AndyG, Jan 27 '17 at 13:26
Or perhaps you can go for overloading the `=` operator and perform the same thing — The Apache, Jan 27 '17 at 13:28
@AndyG - *initialize* has a very specific meaning in C++, and `b = B(*a);` does *not* initialize `b` - it assigns to it. — Martin Bonner supports Monica, Jan 27 '17 at 13:29

score 1 · Accepted Answer · answered Jan 27 '17 at 13:24

1

It should be:

class System{
public:
  System() : a(make_A()), b(*a) {} // use initializer list for constructor
private:
  // Fix order of members to initialize in correct order.
  std::unique_ptr<A> a;
  B b;
};

answered Jan 27 '17 at 13:24

Jarod42

203,559
14
181
302

I edited the question, please give a look at it. – justHelloWorld Jan 27 '17 at 13:43
Created a function `MakeAOrDefault`. – Jarod42 Jan 27 '17 at 13:46
Lol that makes sense – justHelloWorld Jan 27 '17 at 13:46

How to call an object constructor inside another constructor?

1 Answers1