Hello I am submitting once again this patch for the thread library as the issue still exist with 1.33.0. When building boost with msvc-stlport toolset the _snprintf function used at read_write_mutex.cpp:151 is undefined as stdio.h has not been included next to tchar.h include at line 38. In order to have this patch apply this time I have study why _snprintf _is_ defined when using msvc toolset. The conclusion is that the definition comes from the <utility> include in boost/config/select_stdlib_config.hpp which is used to guess what is the std lib. In VC6 utility header include a lot of headers indirectly like cstring, cwchar, xstddef and cstdio which give _snprintf. The STLport utility try to limit the includes, maybe it shouldn't ;-) For your info I discovered an other issue, some guy from boost will have perhaps to work on it. I have only check it with VC6, don't know if it is reproductible with .NET 2002 or 2003. Even if you set your INCLUDE env variable to use the latest PSDK rather than the one integrated in VC6 you are still include of windows.h from boost during build process are still referencing the VC6 windows.h rather than the one of the latest SDK. I thought it was coming from the #include "windows.h" that exists in many VC6 headers but it is not the case. Bests *** read_write_mutex.cpp.orig Tue Aug 23 07:46:00 2005 --- read_write_mutex.cpp Tue Aug 23 19:02:08 2005 *************** *** 36,41 **** --- 36,42 ---- #ifdef BOOST_HAS_WINTHREADS # include <windows.h> # include <tchar.h> + # include <stdio.h> # if !((_WIN32_WINNT >= 0x0400) || (_WIN32_WINDOWS > 0x0400)) inline bool IsDebuggerPresent(void)