While testing gcc 3.4 (on a x86 PC running Linux), I encountered linker errors due to missing pthread symbols, even though my program is single threaded. I found that some translation units using boost::shared_ptr included boost/detail/lwm_nop.hpp whereas other translation units included boost/detail/lwm_pthreads.hpp. I didn't observe any errors with gcc 3.3.x. The problem turns out to be that gcc 3.4 defines the preprocessor variable _REENTRANT if certain standard library headers are included even if the compiler is *not* called with the '-pthread' command line option. The following test exhibits this behavior and shows that it causes BOOST_HAS_THREADS to be erroneously defined in boost/config/suffix.hpp if, e.g., the standard header string is included: cludwig@lap200:~/C++/gcc3.4/tmp> g++ -v Lese Spezifikationen von /opt/gcc/gcc-3.4.0/lib/gcc/i686-pc-linux-gnu/3.4.0/specs Konfiguriert mit: ../gcc-3.4.0/configure --prefix=/opt/gcc/gcc-3.4.0 --enable-threads=posix --enable-version-specific-runtime-libs --enable-languages=c,c++ --enable-__cxa_atexit --enable-c-mbchar --enable-concept-checks --enable-libstdcxx-debug --enable-c99 --enable-libstdcxx-pch Thread-Modell: posix gcc-Version 3.4.0 cludwig@lap200:~/C++/gcc3.4/tmp> cat test-BOOST_HAS_THREADS.cc #if defined(WITH_STRING_HEADER) # include <string> #endif #include <boost/config.hpp> #if defined(__MT__) # warning "__MT__ defined" #endif #if defined(_MT) # warning "_MT defined" #endif #if defined(_REENTRANT) # warning "_REENTRANT defined" #endif #if defined(_PTHREADS) # warning "_PTHREADS defined" #endif #if defined(BOOST_HAS_THREADS) # warning "BOOST_HAS_THREADS defined" #endif cludwig@lap200:~/C++/gcc3.4/tmp> g++ -c -I ../boost_1_31_0/ test-BOOST_HAS_THREADS.cc cludwig@lap200:~/C++/gcc3.4/tmp> g++ -c -I ../boost_1_31_0/ -DWITH_STRING_HEADER test-BOOST_HAS_THREADS.cc test-BOOST_HAS_THREADS.cc:16:4: Warnung: #warning "_REENTRANT defined" test-BOOST_HAS_THREADS.cc:24:4: Warnung: #warning "BOOST_HAS_THREADS defined" I have no idea what the gcc developers recommend in order to detect multi-threading support or if this should be reported to the gcc developers as a bug. But it will certainly break many programs using Boost. A user can work around this problem by either including boost/config.hpp before any other headers (even Boost headers since boost/lexical_cast.hpp, for example, includes string before boost/config.hpp). Or the user builds everything with MT-support, even if the program itself is single threaded. Neither workaround is satisfying. Regards Christoph PS: FWIW, I could trace back the problem to a change in include/c++/i686-pc-linux-gnu/bits/gthr-default.h. This change was discussed in http://gcc.gnu.org/ml/gcc-patches/2003-07/msg01607.html. -- http://www.informatik.tu-darmstadt.de/TI/Mitarbeiter/cludwig.html LiDIA: http://www.informatik.tu-darmstadt.de/TI/LiDIA/Welcome.html