[boost] [Wiki] Changes in information about gcc warnings.

Subject: [boost] [Wiki] Changes in information about gcc warnings.
From: Patrick Horgan (phorgan1_at_[hidden])
Date: 2011-01-10 19:04:41

I did a first cut at adding information to the wiki 
https://svn.boost.org/trac/boost/wiki/Guidelines/WarningsGuidelines for 
the changes in GCC that let you suppress warnings locally.  It's 
probably not useful to you, since it's only in gcc version 4.x and the 
ability to push and pop the current state is very recent, in 4.6.  
Nevertheless it needed documenting.  There's a change to the behavior of 
#pragma GCC system_header as well.  It previously had to be at file 
scope, and now can be anywhere in the file and affects from that point 
forward.  The new pragma:

  #pragma GCC diagnostic <ignored|warning|error> "-WASPECIFICWARNINGOPTION"

used like:

  #pragma GCC diagnostic ignored "-Wdeprecated-declarations".

Prior to 4.6 this also had to be at file scope.  As of 4.6 it can be at 
any line.  With both it affects from that point forward.

  #pragma GCC diagnostic <push|pop>

These two just showed up at 4.6 and can be at any line.  Without them, 
the previous pragma is not that useful because if you affect the users 
flags they will not like you!  lol!  With them you can do what you 
really want:

#pragma GCC diagnostic push
#pragma GCC diagnostic "-Wunitialized"
// your code here
#pragma GCC diagnostic pop

4.6 is the current development trunk, so consider this a heads up.  I'm 
trying to get from the gcc guys a good description of what preprocessor 
checks can be done to determine what's available when.  When I get it, 
I'll add it to the wiki.

Of course, almost all of the time warnings represent real issues and 
it's better to change your code to get rid of the warning and make it 
more correct, than to change your code to have ugly pragmas that 
suppress the warning.

Patrick