At several places in the code we find something like: // BOOST_POSIX or BOOST_WINDOWS specify which API to use. # if !defined( BOOST_WINDOWS ) && !defined( BOOST_POSIX ) # if defined(_WIN32) || defined(__WIN32__) || defined(WIN32) || defined(__CYGWIN__) # define BOOST_WINDOWS # else # define BOOST_POSIX # endif # endif (As in for example boost/libs/filesystem/src/path_posix_windows.cpp) This sets BOOST_WINDOWS explicitely, as default, for cygwin - which is a POSIX operating system with a single root. This breaks a lot of code - if not all - of boost::filesystem. For example, the following code: #include <iostream> #include <boost/filesystem/path.hpp> #include <boost/filesystem/operations.hpp> int main() { boost::filesystem::path p = "/usr"; if (!boost::filesystem::exists(p)) std::cerr << p.string() << " doesn't exist according to boost::filesystem" << std::endl; } indeed causes boost::filesystem::exists to return 'false' on cygwin while "/usr" definitely exists. The reason for that is obvious and looks like a clear bug: The code of boost::filesystem::exists is as follows: BOOST_FILESYSTEM_DECL bool exists( const path & ph ) { # ifdef BOOST_POSIX struct stat path_stat; if(::stat( ph.string().c_str(), &path_stat ) != 0) { if((errno == ENOENT) || (errno == ENOTDIR)) return false; // stat failed because the path does not exist // for any other error we assume the file does exist and fall through, // this may not be the best policy though... (JM 20040330) } return true; # else if(::GetFileAttributesA( ph.string().c_str() ) == 0xFFFFFFFF) { UINT err = ::GetLastError(); if((err == ERROR_FILE_NOT_FOUND) || (err == ERROR_PATH_NOT_FOUND) || (err == ERROR_INVALID_NAME)) return false; // GetFileAttributes failed because the path does not exist // for any other error we assume the file does exist and fall through, // this may not be the best policy though... (JM 20040330) return true; } return true; # endif } Therefore, with BOOST_POSIX undefined, "/usr" is passed directly to ::GetFileAttributesA() and that can obviously not work. My question is therefore: shouldn't BOOST_POSIX be forced to be defined on cygwin? -- Carlo Wood <carlo@alinoe.com> PS Please note that, looking at http://www.meta-comm.com/engineering/boost-regression/developer/summary.html nobody is running the testsuite on cygwin! How broken on cygwin is boost really?