NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/std/c++/954

Text File | 1996-08-06 | 3.7 KB | 94 lines

Path: fido.asd.sgi.com!austern
From: [e-mail] (James Kanze US/ESC 60/3/141 #40763)
Newsgroups: comp.std.c++
Subject: Re: Const class member
Date: 03 Apr 1996 09:22:42 PST
Organization: GABI Software, Sarl.
Approved: [e-mail]
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References: <4jgpqa$[e-mail]> <4jq60l$[e-mail]>
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X-Original-Date: 03 Apr 1996 09:28:02 GMT
In-Reply-To: [e-mail]'s message of 02 Apr 96 13:30:31 GMT
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In article <4jq60l$[e-mail]> [e-mail]
(Torsten Hoff) writes:

|> In article <4jgpqa$[e-mail]>,
|>    [e-mail] (Brian V. McGroarty) wrote:
|> >Is this legal?  Borland and Microsoft compilers will accept the following:
|> >
|> >class AnyClass
|> >{
|> >    const int constInt;
|> >}
|> >
|> >The Borland compiler complains about the uninitialized constant, whereas
|> >the Microsoft compiler does not.  If a constructor is present, both will
|> >complain that the constant isn't initialized in the constructor, however
|> >neither will allow you to assign a value in the constructor by simply
|> >specifying "constInt= some value".  I have also attempted to initialize in
|> >a global variable "int AnyClass::constInt",  to determine whether static
|> >somehow became implicit -- still no go.  If this is legal, how is the value
|> >initialized?
|> [Snip]

|> That's perfectly legal.

|> However, you can't initialize the const member in the class
|> declaration, since you haven't instantiated an object of the class in
|> question which could receive the value. Furthermore, it would prevent
|> you from assigning different values to constInt in different instances
|> of the class, which in most cases is not what you want, either.

|> If you *really* want compile-time initialized constants, and can live
|> with something that has essentially the same properties as an integer,
|> use class-scope enums. If you need several compile-time constants with
|> the same value, you can use multiple untagged enums:

|> class AnyClass
|> {
|>     enum {FOO = 1, BAR = 1}; // multiple enums with same value; doesn't work!

Why not?  It is allowed by the standard, and works on all of the
compilers I've used.

|>     enum {FOO = 1};          // OK
|>     enum {BAR = 1};          // OK
|> }

The (minor) problem with this solution is that the type of the constant
may not be what you want.  This is probably only a problem when function
overloading is present, or templates.

The draft standard allows an initialization of a *static* const in the
class definition, e.g.:

    class X
    {
        static size_t const     mySize = 1024 ;
    } ;

This is a relatively new feature, however, and may not be supported by
your compiler.

    [Rest of correct answer deleted...]
--
James Kanze         Tel.: [phone]        email: [e-mail]
GABI Software, Sarl., 8 rue des Francs-Bourgeois, F-67000 Strasbourg, France
Conseils, Θtudes et rΘalisations en logiciel orientΘ objet --
                -- A la recherche d'une activitΘ dans une region francophone
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