Re: [boost] Re: Coding guidelines - comments

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
 >sounds.
 >
 >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.

--Beman