TITLE: zero initialization of built-in types

PROBLEM: James Kanze <kanze@lts.sel.alcatel.de>

Expressions of the form `int()' have always been allowed.  A (fairly)
recent change to the draft standard states that they have the same
value as default static initialization (in this case, 0).  The earlier
rules had the initailization undefined.


RESPONSE: jamshid@io.com (Jamshid Afshar)

Is the following legal?

	class Foo {
	   int x;
	public:
	   Foo()
	     : x()   // legal?
	   {}
	};

and if so is it different than just:

	Foo::Foo() {}


RESPONSE: fjh@munta.cs.mu.OZ.AU (Fergus Henderson), 28 Feb 96

Yes. [It is legal]

Yes, they are different.  The former is equivalent to

	Foo::Foo() : x(0) {}

This can be deduced from the following sections of the working paper:

	[class.base.init] 12.6.2/3
		"if the *expression-list* of the *mem-initializer* is
		omitted, the base class or member subobject is
		default-initialized (see [dcl.init])"

	[dcl.init] 8.5/5
		"To default-initialize an object of type T means:
		--if T is a non-POD class type ...;
		--if T is an array type ...;
		--otherwise, the storage for the object is zero-initialized."