Calling a default constructor in a constructor argument

Question

I have a class A with a default constructor and a class B with a constructor that takes an object of class A as sole argument.

As a natural way to Create an object of class B I would consider

B b(A());

But the compiler interprets this as a function declaration.

I know that

B b((A()));

or

B b {A()};

are alternatives. But my question is: How can the first version be interpreted as a function declaration? From my point of view it doesn't look like one.

Ok, it's a duplicate. However it is quite hard to find out that the other two questions are related to this issue. — Frank Puffer, Jan 18 '18 at 19:10

JFMR · Accepted Answer · 2018-01-18T18:57:26.633

3

How can the first version be interpreted as a function declaration?

It's just a language rule: In C++ everything that can be interpreted as a declaration will be interpreted as a such.

The following code:

B b(A());

can be interpreted as a declaration of a function whose name is b which:

Returns an object of type B.
Takes a (pointer to a) function as a parameter (the name of the parameter is not provided) that returns an object of type A.

So it will interpreted as a declaration be cause it can be interpreted as a such.

edited Jan 18 '18 at 18:57

answered Jan 18 '18 at 18:47

JFMR

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But how can it be a function declaration? (have slightly modified my question.) – Frank Puffer Jan 18 '18 at 18:50
@FrankPuffer I've updated my answer – JFMR Jan 18 '18 at 18:59

Calling a default constructor in a constructor argument

1 Answers1