I've noticed that the following has been added to the config/stdlib/libstdcpp3.hpp #if defined(__GLIBCXX__) || (defined(__GLIBCPP__) && __GLIBCPP__>=20020514) // GCC >= 3.1.0 # define BOOST_STD_EXTENSION_NAMESPACE __gnu_cxx # define BOOST_HAS_SLIST # define BOOST_HAS_HASH # define BOOST_SLIST_HEADER <ext/slist> # define BOOST_HASH_SET_HEADER <ext/hash_set> # define BOOST_HASH_MAP_HEADER <ext/hash_map> #endif My question is: How is BOOST_SLIST_HEADER intended to be used. At first I thought that one was expected to do something like the following: #ifdef BOOST_HAS_SLIST #include BOOST_SLIST_HEADER #endif But since BOOST_SLIST_HEADER is only defined in config/stdlib/libstdcpp3.hpp other libraries that support define BOOST_HAS_SLIST. On the otherhand if one has to use: #if defined(__GLIBCXX__) || (defined(__GLIBCPP__) && __GLIBCPP__>=20020514) // GCC >= 3.1.0 then whats point of defining BOOST_SLIST_HEADER rather than just using #include <ext/slist> What should I be doing here? Robert Ramey