https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67996
--- Comment #4 from Kim Gräsman <kim.grasman at gmail dot com> --- FWIW, it turns out that GCC warns, too: $ g++ -Iinclude -I/ssd/code/poco/CppUnit/include -I/ssd/code/poco/CppUnit/WinTestRunner/include -I/ssd/code/poco/Foundation/include -I/ssd/code/poco/XML/include -I/ssd/code/poco/Util/include -I/ssd/code/poco/Net/include -I/ssd/code/poco/Crypto/include -I/ssd/code/poco/NetSSL_OpenSSL/include -I/ssd/code/poco/Data/include -I/ssd/code/poco/Data/SQLite/include -I/ssd/code/poco/Data/ODBC/include -I/ssd/code/poco/Data/MySQL/include -I/ssd/code/poco/Zip/include -I/ssd/code/poco/PageCompiler/include -I/ssd/code/poco/PageCompiler/File2Page/include -I/ssd/code/poco/PDF/include -I/ssd/code/poco/CppParser/include -I/ssd/code/poco/MongoDB/include -I/ssd/code/poco/PocoDoc/include -I/ssd/code/poco/ProGen/include -Wall -Wno-sign-compare -DPOCO_UTIL_NO_JSONCONFIGURATION -DPOCO_HAVE_IPv6 -D_XOPEN_SOURCE=500 -D_REENTRANT -D_THREAD_SAFE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE64_SOURCE -DPOCO_HAVE_FD_EPOLL -O2 -DNDEBUG -fPIC -c src/MemoryStream.cpp -o /ssd/code/poco/Foundation/obj/Linux/x86_64/release_shared/MemoryStream.o In file included from src/MemoryStream.cpp:17:0: include/Poco/MemoryStream.h: In instantiation of ‘Poco::BasicMemoryStreamBuf<ch, tr>::pos_type Poco::BasicMemoryStreamBuf<ch, tr>::seekoff(Poco::BasicMemoryStreamBuf<ch, tr>::off_type, std::ios_base::seekdir, std::ios_base::openmode) [with ch = char; tr = std::char_traits<char>; Poco::BasicMemoryStreamBuf<ch, tr>::pos_type = std::fpos<__mbstate_t>; Poco::BasicMemoryStreamBuf<ch, tr>::off_type = long int; std::ios_base::seekdir = std::_Ios_Seekdir; std::ios_base::openmode = std::_Ios_Openmode]’: src/MemoryStream.cpp:59:1: required from here include/Poco/MemoryStream.h:87:4: warning: enumeration value ‘_S_ios_seekdir_end’ not handled in switch [-Wswitch] switch (way) ^ include/Poco/MemoryStream.h:113:4: warning: enumeration value ‘_S_ios_seekdir_end’ not handled in switch [-Wswitch] switch (way) ^ This is the age-old GCC 4.6.3 that we're stuck on, however, later versions may be more forgiving.