Hello,

I thought that

  class X {};

is a definition, while

  class X;

is a declaration.

Now I heard  someone talking about a "forward declaration". Can
someone please explain what a forward-declaration is?

Thanks - Martin

------------------------------------------------
Martin Aupperle
MikeAlpha@NoSpam_csi.com
(remove NoSpam_)
------------------------------------------------

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"Martin Aupperle" <MikeAlpha@NoSpam_csi.com> wrote in message
news:3b4a9d99.159247515@news.nikoma.de...
> Hello,
>
> I thought that
>
>   class X {};
>
> is a definition, while
>
>   class X;
>
> is a declaration.
>
> Now I heard  someone talking about a "forward declaration". Can
> someone please explain what a forward-declaration is?

A forward declaration is just a declaration. However, it usually refers to
the particular case where something is declared at the top of a source file,
and then declared later in the same source file. This way, anything declared
or defined in between can refer to the object/class/function, as a
declaration (at least) must always be seen before use.

e.g.

int f(int,double); // (forward) declaration

int g()
{
    return f(2,3.7); // needs declaration of f() above
}

int f(int a,double d) // definition of f.
{
    // do some stuff
    return a;
}

Anthony
--
Anthony Williams
Software Engineer, Nortel Networks Optoelectronics
The opinions expressed in this message are not necessarily those of my
employer



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On Wed, 11 Jul 2001 17:00:25 GMT, MikeAlpha@NoSpam_csi.com (Martin
Aupperle) wrote:
>I thought that
>
>  class X {};
>
>is a definition, while
>
>  class X;
>
>is a declaration.
>
>Now I heard  someone talking about a "forward declaration". Can
>someone please explain what a forward-declaration is?

The terms "declaration" and "definition" when applied to classes have
tradtionally been somewhat muddled. It is common to see
 class X { };
referred to as either a declaration or a definition -- sometimes in
the same book or article.

I think it is helpful to maintain the same distinction for classes
that we have for functions, as in your usage above. Using the
terminology that way, a "forward declaration" is just a declaration.

But if you describe
 class X { };
as a "declaration", you then need some other term for
 class X;
The original C standard uses the term "forward delcaration."
---
Steve Clamage, stephen.clamage@sun.com

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