GCC -wundef warnings

[anonymous]

Compiling code that includes Boost headers with gcc -wundef produces a lot of warnings about undefined preprocessor symbols, mainly in BOOST_WORKAROUND(XXX, ...) where XXX is not defined.

Example:

boost/filesystem/fstream.hpp line 103:

#   if !BOOST_WORKAROUND( BOOST_MSVC, <= 1200 ) // VC++ 6.0 can't handle this

should probably be

#   if defined( BOOST_MSVC ) && !BOOST_WORKAROUND( BOOST_MSVC, <= 1200 )

[andyc@…]

I notice that this problem has been discussed previously on <​http://lists.boost.org/Archives/boost/2005/10/95850.php> and there's a proposal to do with BoostConfig referenced there: <​http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl?BoostConfig>.

I also notice that that's proposing using constructs such as:

Comeau C++ #ifndef BOOST_CXX_COMO #define BOOST_CXX_COMO 0 #endif

I wonder if you could use this instead:

# define BOOST_WORKAROUND(symbol, test) \

((BOOST_COMPILER_DEFINED_ ## symbol) && \

(symbol != 0) && (1 % (( (symbol test) ) + 1)))

and you could then define

#define BOOST_COMPILER_DEFINED_BOOST_MSVC defined(BOOST_MSVC)

for each macro used in a BOOST_WORKAROUND expansion rather than all those #ifndefs. Just a thought. (I also did wonder whether there was some preprocessor magic to save having to define all those by hand but I couldn't come up with any).

Until this problem is resolved in an official boost release, that's what we're intending to do so that we can compile with -Wundef.

-- Andy, BlueArc Engineering

[John Maddock]

I'm working on this now, hopefully we'll work something out!

[John Maddock]

This is hopefully now fixed with this changeset: ​http://svn.boost.org/trac/boost/changeset/39473/trunk/boost/detail/workaround.hpp

Note that the logic we've used is the reverse of yours: the danger with your suggested fix is that if you use BOOST_WORKAROUND with a macro about which it knows nothing, then it will always evaluate to false :-(

Regards, John Maddock.