I ran across a case this morning where the FormatMessage Win32 call in boost::system_error_category::message() fails (the error message table did not have an entry for the error code that was passed). Unfortunately, when this happens lpMsgBuf is not initialized to anything and trying to use it can result in an access violation. The attached patch adds checks to catch situations where FormatMessage fails. Thanks, -Dave Index: error_code.cpp =================================================================== --- error_code.cpp (revision 40686) +++ error_code.cpp (working copy) @@ -347,7 +347,7 @@ { # ifndef BOOST_NO_ANSI_APIS LPVOID lpMsgBuf; - ::FormatMessageA( + DWORD retval = ::FormatMessageA( FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS, @@ -358,11 +358,14 @@ 0, NULL ); + if (retval == 0) + return std::string(); + std::string str( static_cast<LPCSTR>(lpMsgBuf) ); ::LocalFree( lpMsgBuf ); // free the buffer # else // WinCE workaround LPVOID lpMsgBuf; - ::FormatMessageW( + DWORD retval = ::FormatMessageW( FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS, @@ -373,10 +376,13 @@ 0, NULL ); + if (retval == 0) + return std::string(); int num_chars = (wcslen( static_cast<LPCWSTR>(lpMsgBuf) ) + 1) * 2; LPSTR narrow_buffer = (LPSTR)_alloca( num_chars ); - ::WideCharToMultiByte(CP_ACP, 0, static_cast<LPCWSTR>(lpMsgBuf), -1, narrow_buffer, num_chars, NULL, NULL); + if (::WideCharToMultiByte(CP_ACP, 0, static_cast<LPCWSTR>(lpMsgBuf), -1, narrow_buffer, num_chars, NULL, NULL) == 0) + return std::string(); std::string str( narrow_buffer ); ::LocalFree( lpMsgBuf ); // free the buffer