Re: [boost] Boost.Build/Boost.Jam issues w/ gcc v302

From: Ronald Garcia (garcia_at_[hidden])
Date: 2002-08-14 16:23:40

David Abrahams wrote:

>----- Original Message -----
>From: "Ronald Garcia" <garcia_at_[hidden]>
>
>
>  
>
>>David Abrahams wrote:
>>
>>    
>>
>>>I don't know what you mean; you've done the best analysis I've seen to
>>>date. Headers found through -isystem should be allowed to contain C++
>>>      
>>>
>code!
>  
>
>>>
>>>      
>>>
>>At the time I was thinking that perhaps -isystem should not set
>>different line number flags at all, but upon checking the docs again I
>>see that it does call for special treatment of headers, at least with
>>regard to warnings.
>>    
>>
>
>Really? For all platforms? Because we're not seeing any issues on other
>platforms.
>
Well, the docs say the following:
`-isystem DIR'
     Add a directory to the beginning of the second include path,
     marking it as a system directory, so that it gets the same special
     treatment as is applied to the standard system directories.

My best guess is that the "special treatment" it is talking about is 
whatever the compiler does when it sees the "3" flag on  line numbering 
directives (which are added by the preprocessor).  
I have tried a few versions of gcc on linux and solaris.  The difference 
between linux and solaris seems to
be the addition of the "4" flag to line numbers (treat the following 
text as C). Aye, there's the rub!

With that solved ( :) ), the question is what special treatment system 
headers are given by gcc.  The docs for the line number directives say 
the following:

   Source file name and line number information is conveyed by lines of
the form
 
     # LINENUM FILENAME FLAGS
...
   After the file name comes zero or more flags, which are `1', `2',
`3', or `4'.  If there are multiple flags, spaces separate them.  Here
is what the flags mean:
...
`3'
     This indicates that the following text comes from a system header
     file, so certain warnings should be suppressed.

I presume that this is meant to allow the compiler/std-lib implementors 
to get away with some warning-able constructs. My worry is that some 
warnings in boost libraries might be suppressed by the use of -isystem, 
but I don't know what warnings those are.

ron