Using constructor of an object within another class

Question

I created a class with a constructor that takes an int to determine the size of a linked list the object has. The problem I'm having is I need to be able to call this constructor when this object is instantiated as a private member of another class. So basically:

class A {
public:
    A();
    A(int size);
};

class B {
    const int size = // any number > 0
private:
    A a(size);
};

I get this error:

constant "B::size" is not a type name

I've tried searching online, but I can't come across this specific issue. It could be that I'm struggling to word the question correctly... it's a weird issue I haven't seen yet. Any help is appreciated!

You have declared methods but you have not implemented them. Where's the implementation? — merlin2011
– merlin2011, Commented May 11, 2014 at 8:46
That's a faulty design. I suggest you ask about the actual problem you are trying to solve, and not about the solution you had in mind. — StoryTeller - Unslander Monica
– StoryTeller - Unslander Monica, Commented May 11, 2014 at 8:47
The constructor for A should be called in the constructor for B. You can't instantiate directly in a header file unless you are using a constant. — donutmonger
– donutmonger, Commented May 11, 2014 at 8:48
Your declaration of A a(size); is wrong, should be A a; and initialize the a member in class B's constructor member initialization list. — πάντα ῥεῖ
– πάντα ῥεῖ, Commented May 11, 2014 at 8:48

tpatja · Accepted Answer · 2014-05-11 08:47:27Z

3

You cannot call the constructor with parameters in the member variable declaration.

You can implement a constructor for B and do it there.

B::B() : a(size) {}

answered May 11, 2014 at 8:47

tpatja

6824 silver badges11 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

VagrantC Over a year ago

Thank you! That's exactly what I was looking for. I have no idea why I didn't try that...

Some programmer dude · Accepted Answer · 2014-05-11 08:48:09Z

2

You have to do in the B constructor, using an initializer list:

class B
{
public:
    B() : a(size)
    {}

private:
    A a;
    const int size = ...;
};

answered May 11, 2014 at 8:48

Some programmer dude

411k36 gold badges420 silver badges655 bronze badges

Collectives™ on Stack Overflow

Using constructor of an object within another class

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related