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From: Beman Dawes (bdawes_at_[hidden])
Date: 2001-07-05 16:46:33

At 04:11 PM 7/5/2001, williamkempf_at_[hidden] wrote:

>I'd like some clarifications here if anyone wants to help me out.
>I've searched the C++ standard for this and have found 16.2 relating
>to this topic. 16.2/2 simply says that #include <...> shall search
>for a header in a sequence of implementation defined places and
>doesn't mention "system headers" at all. 16.2/3 says that
>#include "..." shall search for the file in an implementation defined
>manner, and if not supported or the search fails it will try again as
>if it were #include <...>. So I can find no mention of "system
>headers". In fact, there's no help from the standard in
>understanding when to use which style, other than you're gauranteed
>to find the header (if it can be found) using "..." while you may not
>find it using <...>.
>The talk of system headers just confuses the issue. What is a system
>header? Does this mean a standard header, or simply a header
>provided by the vendor, such as Windows.h on the Windows platform?
>Why should either be given any kind of special treatment over other
>library supplied headers?
>I'm used to VC++ where the rules are detailed better. A #include
><...> will search for the header in all directories specified on the
>command line or in the INCLUDE environment variable. A
>#include "..." will search in the current directory, and if that
>fails it will retry as if it were #include <...> as per the
>standard. This makes usage rules a little easier to define. If the
>header is part of the current project you use "...", if it's part of
>a seperate library you use <...>. This gives a *slight* optimization
>in the searching for both file types, and makes it easier for readers
>of the code to find the files as well. Because of this, that's the
>convention I've always followed.
>However, with what I've read in the standard and with other things
>discussed here it seems like the only sensible guideline for portable
>code is to use #include "..." for ALL header files, as dumb as that
>What's the historical reasoning behind having both forms? Are there
>other sections in the standard that define any of this better than
>those I've referenced? Who's responsible for this mess? ;)

I think the C++ wording is carried over from C. But it really is unclear,
so I think a defect report is called for.


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