Re: [Boost-users] [Spirit] dereferencing type-punned pointer will break strict-aliasing rules

Subject: Re: [Boost-users] [Spirit] dereferencing type-punned pointer will break strict-aliasing rules
From: David Abrahams (dave_at_[hidden])
Date: 2010-08-11 18:14:26

At Wed, 11 Aug 2010 11:59:21 -0700,
Emil Dotchevski wrote:
> 
> On Wed, Aug 11, 2010 at 1:37 AM, Roland Bock <rbock_at_[hidden]> wrote:
> > Hi,
> >
> > compiling the attached example with gcc-4.4.3 (Ubuntu 10.4, 64bit) with
> >
> > -Wall -O3
> >
> > leads to a long warning message (second attachment), culminating in
> >
> > boost/1.44/include/boost/function/function_base.hpp:321: warning:
> > dereferencing type-punned pointer will break strict-aliasing rules
> > boost/1.44/include/boost/function/function_base.hpp:325: warning:
> > dereferencing type-punned pointer will break strict-aliasing rules
> >
> >
> > I wonder how I could avoid this without -fno-strict-aliasing or
> > -Wno-strict-aliasing?
> 
> The code in question is a reinterpret_cast which casts a char pointer
> to a user-specified functor type pointer. The interpret cast seems
> correct, and the warning seems correct too if not very useful in this
> case.

Really, the reinterpret_cast is portably correct?  Pretty much the
only thing you can do portably with reinterpret_cast is round-trip
cast a pointer type to another pointer type and then cast it back
before you use it again.

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com