Re: [Boost-users] [wave] Tracing a macro in a preprocessor directive

Subject: Re: [Boost-users] [wave] Tracing a macro in a preprocessor directive
From: Edward Diener (eldiener_at_[hidden])
Date: 2011-08-30 10:04:09

On 8/30/2011 5:12 AM, Paul Mensonides wrote:
> On Mon, 29 Aug 2011 15:27:43 -0400, Edward Diener wrote:
>
>> I was trying to trace the output of a macro within a preprocessor
>> directive in a file using the Wave trace facility. The directive is:
>>
>> #elif BOOST_PP_ITERATION_FLAGS() == 1
>>
>> so I specified:
>>
>> #pragma wave trace(enable)
>> #elif BOOST_PP_ITERATION_FLAGS() == 1 #pragma wave trace(disable)
>>
>> But wave's trace showed me an empty file where the macro output (
>> -tsomefile ) should have been.
>>
>> Is there a way to capture the output of the BOOST_PP_ITERATION_FLAGS()
>> macro at the point where the #elif is occuring using Wave's trace
>> facility ?
>
> If this is from the curryable.hpp file, gcc does attempt to parse all of
> the #if/#elif directives for the level it is currently on.  E.g.
>
> #if !BOOST_PP_IS_ITERATING // okay, will "decay" to 0 if not defined
>
> // ...
>
> #elif BOOST_PP_ITERATION_FLAGS() == 2 // will cause error
>     // when not iterating, iteration flags is not defined
>     // so this will result in 0() == 2 which is a syntax error
>
> // ...
>
> #endif
>
> The "problem" is that gcc requires a well-formed expression even if the
> first branch of #if is taken.  The fix is to do this:
>
> #if !BOOST_PP_IS_ITERATING
>
> // ...
>
> #else
>
>      #if BOOST_PP_ITERATION_FLAGS() == 2
>
>          // ...
>
>      #endif
>
> #endif

It is indeed curryable.hpp. I made the changes you suggest above to 
curryable.hpp. A normal compile using gcc now works without errors 
against Boost PP on the trunk ( your iteration changes work ) , but 
still gives the same errors as before against Boost 1.47:

In file included from 
C:\Utilities\Boost\boost_1_47_0/boost/preprocessor/iteration/detail/iter/forward2.hpp:50:0,
                  from ..\..\../curryable.hpp:158,
                  from 
C:\Utilities\Boost\boost_1_47_0/boost/preprocessor/iteration/detail/iter/forward1.hpp:47,
                  from ..\..\../curryable.hpp:113,
                  from curryable.cpp:1:
..\..\../curryable.hpp:118:1: error: macro "BOOST_PP_CHECK_2" requires 2 
arguments, but only 1 given
..\..\../curryable.hpp:118:1: error: macro "BOOST_PP_CHECK_2" requires 2 
arguments, but only 1 given
..\..\../curryable.hpp:118:1: error: pasting ")" and "BOOST_PP_CAT" does 
not give a valid preprocessing token
..\..\../curryable.hpp:177:1: error: macro "BOOST_PP_CHECK_2" requires 2 
arguments, but only 1 given
..\..\../curryable.hpp:177:1: error: macro "BOOST_PP_CHECK_2" requires 2 
arguments, but only 1 given
..\..\../curryable.hpp:177:1: error: pasting ")" and "BOOST_PP_CAT" does 
not give a valid preprocessing token