Constructor Syntax

[seppel]

Having defined a class A with several constructors and a default constructor the statement A a( x ); calls the corresponding constructor, given it is defined, depending on the type of x. Hence you could guess that A a( ); should call the default constructor as it is defined with empty brackets A::A( ){}. But you must write A a; without brackets instead of A a(); even if the syntax without brackets doesnt fit smoothly into the general syntax of constuctor calls. Could somebody please give some insight why the syntax is defined this way? Thanks!

[zb0S216C]

A a()

This declaration doesn't invoke the default constructor, but declares a prototype function, so the compiler thinks.

_Wazzak

[Peter87]

If something can be a function declaration it is a function declaration.
When you write A a(); the compiler will treat this as a function declaration of a function named a that takes no arguments and returns an A object.

[seppel]

Is a function declaration/prototype in a function body C++ compliant?

[Peter87]

yes

[ne555]

Hence you could guess that A a( ); should call the default constructor

But that overlaps with a function declaration.

even if the syntax without brackets doesnt fit smoothly into the general syntax of constuctor calls

However for POD you wouldn't use parenthesis.

[seppel]

Thanks!

[Peter87]

ne555 wrote:

However for POD you wouldn't use parenthesis.

Why not? When using dynamic memory allocations with POD types parenthesis even makes a difference.

Here *p is undefined
int* p = new int;

Here *p is initialized to 0
int* p = new int();

[zb0S216C]

Users.Peter87.Respect++;

_Wazzak