Re: non-const static member variale initialization

From:
"Igor Tandetnik" <itandetnik@mvps.org>
Newsgroups:
microsoft.public.vc.language
Date:
Sun, 10 Feb 2008 14:33:29 -0500
Message-ID:
<uRnjSvBbIHA.5400@TK2MSFTNGP03.phx.gbl>
"George" <George@discussions.microsoft.com> wrote in message
news:908CAFEE-85A3-4B80-9E65-18392FA4F1B3@microsoft.com

Your reply is great! But I do not quite understand this. I think in
this situation, declaration is not the same as definition


Yes, a declaration of a static data member of a class is not a
definition (if that's what you mean by "this situation"). The definition
must be provided separately. Which is precisely what Giovanni showed you
in his very first response.

There is a special exception for static data members of integral or
enumeration types:

9.4.2/4 If a static data member is of const integral or const
enumeration type, its declaration in the class definition can specify a
constant-initializer which shall be an integral constant expression
(5.19). In that case, the member can appear in integral constant
expressions within its scope. The member shall still be defined in a
namespace scope if it is used in the program and the namespace scope
definition shall not contain an initializer.

The wording is further clarified by resolutions to defect reports #48
and #454:

http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#48
http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#454

In particular, DR454 clarifies the definition of "used" to exclude
situations where the object's name appears as an integral constant
expression (basically, where a literal could appear instead).

How could we declare a static data member variable in initializer


Huh? I think you have badly misread the quote. Let me try and introduce
additional punctuation to make it clearer:

3.1/2 A declaration is a definition except in the following cases:
    - it declares a function without specifying the function's body
(8.4);
    - it contains the extern specifier (7.1.1) or a
linkage-specification (7.5), and it doesn't contain an initializer or
a function-body;
    - it declares a static data member in a class declaration (9.4);
    - it is a class name declaration (9.1);
    - it is a typedef declaration (7.1.3);
    - it is a using-declaration (7.3.3);
    - it is a using-directive (7.3.4).

--
With best wishes,
    Igor Tandetnik

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necessarily a good idea. It is hard to be sure where they are going to
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