Re: Destructors can copying objects

From	"Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com>
Newsgroups	comp.lang.c++
Subject	Re: Destructors can copying objects
Date	2011-04-16 01:47 +0200
Organization	A noiseless patient Spider
Message-ID	<ioaldo$4o8$1@dont-email.me> (permalink)
References	<in76i3$105$2@reader1.panix.com> <in78aa$100$1@tota-refugium.de> <in8ob0$ju1$4@reader1.panix.com> <4d984899$0$6987$9b4e6d93@newsspool4.arcor-online.net> <ioaisv$sah$1@reader1.panix.com>

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* Ruben Safir, on 16.04.2011 01:03:
> On Sun, 03 Apr 2011 12:14:40 +0200, Peter Remmers wrote:
>
>> Am 03.04.2011 05:08, schrieb Ruben Safir:
>>>
>>> #ifndef  LINKLIST
>>> #define LINKLIST
>>> #include	"linklist.h"
>>> #endif     /* -----  not LINKLIST  ----- */
>>
>> Include guards should be inside the header, not outside it in the
>> source?
>
> please explain
>
> should the #endif be at the end of the file and why?

It depends on whether it's an external include guard (where you're including the 
header) or an internal include guard (the ordinary kind of include guard, in the 
header file). The idea in any case is to ensure that the text of the header is 
included only once. You can figure it out from there.

External include guards were discussed in Lakos' "Large scale software design". 
They're no longer much used. Compiler technology has improved.

For an internal include guard the usual pattern is now

   #ifndef SOME_UNIQUE_SYMBOL
   #define SOME_UNIQUE_SYMBOL

   //... text of header file

   #endif

An alternative that is /non-standard/ and /not entirely reliable/, but that is 
textually much cleaner, is to use a '#pragma once', like so:

   #pragma once

   //... text of header file

The pragma is problematic when one employs symbolic links to files. The compiler 
may then be unable to detect that two or more links yield the same file. Hence, 
the pragma may be preferable for a small personal project, but not as the single 
single-include-measure for a larger project with more devlopers involved (some 
of whom may suddenly be using symbolic links). When combined with internal 
include guards it may however reduce build times, and it may be necessary due to 
non-standard behavior such as Microsoft's "precompiled headers". Whether it 
actually does reduce build times or have other beneficial or necessary effect, 
depends on the compiler etc.

Cheers & hth.,

- Alf

-- 
blog at <url: http://alfps.wordpress.com>

Thread

Destructors can copying objects Ruben Safir <ruben@mrbrklyn.com> - 2011-04-02 12:58 +0000
  Re: Destructors can copying objects Volker Lukas <vlukas@gmx.de> - 2011-04-02 15:29 +0200
    Re: Destructors can copying objects Ruben Safir <ruben@mrbrklyn.com> - 2011-04-03 02:59 +0000
      Re: Destructors can copying objects "Balog Pal" <pasa@lib.hu> - 2011-04-03 11:32 +0200
        Re: Destructors can copying objects Leigh Johnston <leigh@i42.co.uk> - 2011-04-03 12:29 +0100
          Re: Destructors can copying objects Bart van Ingen Schenau <bart@ingen.ddns.info> - 2011-04-04 13:43 +0200
            Re: Destructors can copying objects Michael Doubez <michael.doubez@free.fr> - 2011-04-05 01:26 -0700
          Re: Destructors can copying objects Joshua Maurice <joshuamaurice@gmail.com> - 2011-04-04 14:03 -0700
            Re: Destructors can copying objects Ruben Safir <ruben@mrbrklyn.com> - 2011-04-04 21:10 +0000
            Re: Destructors can copying objects Leigh Johnston <leigh@i42.co.uk> - 2011-04-04 22:28 +0100
          Re: Destructors can copying objects Ruben Safir <ruben@mrbrklyn.com> - 2011-04-04 21:07 +0000
            Re: Destructors can copying objects Leigh Johnston <leigh@i42.co.uk> - 2011-04-04 22:31 +0100
              Re: Destructors can copying objects Leigh Johnston <leigh@i42.co.uk> - 2011-04-04 22:43 +0100
              Re: Destructors can copying objects Ruben Safir <ruben@mrbrklyn.com> - 2011-04-04 22:38 +0000
                Re: Destructors can copying objects Leigh Johnston <leigh@i42.co.uk> - 2011-04-04 23:42 +0100
                Re: Destructors can copying objects Ruben Safir <ruben@mrbrklyn.com> - 2011-04-04 22:54 +0000
      Re: Destructors can copying objects James Kanze <james.kanze@gmail.com> - 2011-04-03 10:07 -0700
        Re: Destructors can copying objects Ruben Safir <ruben@mrbrklyn.com> - 2011-04-04 21:14 +0000
        Re: Destructors can copying objects Ruben Safir <ruben@mrbrklyn.com> - 2011-04-04 21:17 +0000
          Re: Destructors can copying objects LR <lruss@superlink.net> - 2011-04-05 01:52 -0400
    Re: Destructors can copying objects Ruben Safir <ruben@mrbrklyn.com> - 2011-04-03 03:08 +0000
      Re: Destructors can copying objects Paavo Helde <myfirstname@osa.pri.ee> - 2011-04-03 02:11 -0500
      Re: Destructors can copying objects Volker Lukas <vlukas@gmx.de> - 2011-04-03 12:02 +0200
      Re: Destructors can copying objects Peter Remmers <p.remmers@expires-2011-04-30.arcornews.de> - 2011-04-03 12:14 +0200
        Re: Destructors can copying objects Roberto Waltman <usenet@rwaltman.com> - 2011-04-03 18:16 -0400
          Re: Destructors can copying objects Ruben Safir <ruben@mrbrklyn.com> - 2011-04-15 23:06 +0000
            Re: Destructors can copying objects LR <lruss@superlink.net> - 2011-04-15 19:19 -0400
        Re: Destructors can copying objects Ruben Safir <ruben@mrbrklyn.com> - 2011-04-15 23:03 +0000
          Re: Destructors can copying objects "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-04-16 01:47 +0200
            Re: Destructors can copying objects Peter Remmers <p.remmers@expires-2011-04-30.arcornews.de> - 2011-04-16 13:00 +0200
              Re: Destructors can copying objects "Alf P. Steinbach /Usenet" <alf.p.steinbach+usenet@gmail.com> - 2011-04-16 15:57 +0200
  Re: Destructors can copying objects LR <lruss@superlink.net> - 2011-04-02 09:51 -0400
  Re: Destructors can copying objects Yannick Tremblay <yannick@tremnblay.co.uk> - 2011-04-04 12:56 +0000
    Re: Destructors can copying objects Ruben Safir <ruben@mrbrklyn.com> - 2011-04-04 21:05 +0000
      Re: Destructors can copying objects Paavo Helde <myfirstname@osa.pri.ee> - 2011-04-04 21:56 -0500
      Re: Destructors can copying objects Yannick Tremblay <yannick@tremnblay.co.uk> - 2011-04-05 11:36 +0000
        Re: Destructors can copying objects Ruben Safir <ruben@mrbrklyn.com> - 2011-04-05 15:40 +0000
          Re: Destructors can copying objects Sana <sanatakos@gmail.com> - 2011-04-05 10:11 -0700
          Re: Destructors can copying objects Ruben Safir <ruben@mrbrklyn.com> - 2011-04-05 20:28 +0000
          Re: Destructors can copying objects Yannick Tremblay <yannick@tremnblay.co.uk> - 2011-04-06 11:12 +0000
      Re: Destructors can copying objects drew@furrfu.invalid (Drew Lawson) - 2011-04-05 13:02 +0000
        Re: Destructors can copying objects Ruben Safir <ruben@mrbrklyn.com> - 2011-04-05 15:51 +0000
          Re: Destructors can copying objects drew@furrfu.invalid (Drew Lawson) - 2011-04-05 17:47 +0000
            Re: Destructors can copying objects Ruben Safir <ruben@mrbrklyn.com> - 2011-04-05 20:25 +0000
              Re: Destructors can copying objects drew@furrfu.invalid (Drew Lawson) - 2011-04-05 20:37 +0000

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