Hi, $ g++ --version g++ (GCC) 3.4.2 [FreeBSD] 20040728 (boost version 1.32) When compiling a very simple example for the regex library, I've got the following error: In file included from /usr/local/include/boost_1_32_0/boost/regex/v4/regex.hpp:99, from /usr/local/include/boost_1_32_0/boost/regex.hpp:34, from regex.cc:1: /usr/local/include/boost_1_32_0/boost/regex/v4/instances.hpp:71: error: ISO C++ forbids the use of `extern' on explicit instantiations *** Error code 1 A short investigation points to the following code in the instances.hpp file: #elif (defined(BOOST_MSVC) && defined(_MSC_EXTENSIONS)) || defined(__GNUC__) # ifndef BOOST_REGEX_INSTANTIATE # define template extern template // (*) # endif # ifdef BOOST_MSVC # pragma warning(push) # pragma warning(disable : 4251 4231 4660) # endif template class BOOST_REGEX_DECL reg_expression< BOOST_REGEX_CHAR_T >; IMHO (and rather guessing), the #define in (*) is performed unnecessarily for g++ 3.4.2, but is executed just because of too generic __GNUC__ a little bit higher. As a temporary solution, I have just uncommented the following line in boost/regex/user.hpp: #define BOOST_REGEX_NO_EXTERNAL_TEMPLATES Now the simple program compiles and works fine. What influence will the above change in user.hpp have on bigger programs? Is this a known problem? -- Maciej Sobczak : http://www.msobczak.com/ Programming : http://www.msobczak.com/prog/