Creating object of non pointer type in C++

Question

If i have a class like as below.

class A {
int data;
};

A a; // Case1: calling explicit Default constructor
A b(); // Case2: Calling implicit default constructor

What is the difference between Case1 and Case2?

score 9 · Answer 1 · answered Sep 16 '13 at 11:40

9

A b();

it does not define an object, it declares a function which returns type A, It's also well known as most vexing parse.

answered Sep 16 '13 at 11:40

billz

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+1; knew it had a technical name – Bathsheba Sep 16 '13 at 11:44

score 2 · Answer 2 · answered Sep 16 '13 at 11:42

2

A b(); // Case2: Calling implicit default constructor

The comment is incorrect. A b(); is a function declaration (The function is called b and returns an object of type A and you intend to define the function later) not an object definition.

answered Sep 16 '13 at 11:42

Bathsheba

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It isn't incorrect. It's just not what he thought it was. – user207421 Sep 16 '13 at 11:44
1

@EJP: the comment is wrong. Incorrect comments are worse than no comments. I've amended my answer. – Bathsheba Sep 16 '13 at 11:45
Agreed, but that isn't what you said originally, i.e. what I commented on. – user207421 Sep 16 '13 at 11:46
@EJP: Indeed. The line as a whole has incorrectness in it though. Still, due to the excellence of the other answer, I'll probably remove this one: it adds nothing. – Bathsheba Sep 16 '13 at 11:47

score 0 · Answer 3 · answered Sep 16 '13 at 11:54

Case 1:

    A a; // Case1: calling explicit Default constructor

Calls the implicit default constructor, since you hadn't provided one in the class.

Case 2:

   A b(); // Case2: Calling implicit default constructor

It is the function decleration say "b" is the function name and it takes no argument and returns A object.

Hope it helps.

Creating object of non pointer type in C++

3 Answers3