Re: [Boost-users] Patch for building Boost with GCC 4.4.0

From: Chris Fairles (chris.fairles_at_[hidden])
Date: 2008-06-18 18:03:54

On Wed, Jun 18, 2008 at 11:18 AM, Frank Mori Hess <frank.hess_at_[hidden]> wrote:
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> On Wednesday 18 June 2008 08:52 am, Chris Fairles wrote:
>> On Wed, Jun 18, 2008 at 8:51 AM, Chris Fairles <chris.fairles_at_[hidden]>
> wrote:
>> > GCC changed the way #elif's are handled (is now more std-compliant
>> > apparently) but this broke all the #elif BOOST_PP_ITERATION_DEPTH() ==
>> > N lines. They need to be replaced with
>> >
>> > #elif defined(BOOST_PP_ITERATION_DEPTH)
>> > #if BOOST_PP_ITERATION_DEPTH == N
>> > ...
>> > #endif
>
> Does it work if you do
>
> #elif defined(BOOST_PP_ITERATION_DEPTH) && BOOST_PP_ITERATION_DEPTH() == N
>
> then you could avoid adding the extra #endif
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Unfortunately no. I thought at first it would, but gcc 4.4 still
complains. Reading the std (albeit, n2606, the c++0x draft) it seems
this is incorrect since the tokens after the pp directive combine to
form a constant-expression and constant-expressions can be short
circuited. There may be some special rule for the logical && in pp
const-exprs saying that sub-expressions can be evaluated out of order,
but I couldn't find anything.