(In reply to Kim Gräsman from comment #0)
> What's the motivation for _S_ios_seekdir_end? Any chance it could be removed?

Presumably to make sure the enum type is more than 16-bits, which could be done with a fixed underlying type in C++11, but not in C++03.

I don't think we should change this just because of a warning. The std::lib is allowed to define whatever enumerators it wants to (as long as they use reserved names).

Thanks, I figured that was why.

The warning is not a problem if I'm using <ios> directly, then I can just disable it locally.

But we ran into this with a third-party library having the code above in one of their headers. This makes it nigh-impossible for us to enable -Wswitch for our own code, as the third-party header could be indirectly included in any translation unit.

  ios:
     enum seekdir { beg, cur, end, _S_ios_seekdir_end };

  third-party.h:
    switch(seekdir) {
    case beg: break;
    case cur: break;
    case end: break;
    }

  us.cpp:
    #include "third-party.h"  // WARN

I wasn't sure if the extra enumerator was allowed by the standard, so thanks for confirming that.

We've now worked around it by patching the third-party to use an if/else chain instead, but I thought I'd raise it anyway because it creates a messy situation when the warning "leaks" like this.

Then maybe the warning needs to be smarter, e.g. not warn for enumerators defined in system headers using the implementation's reserved names.

In any case, it's not a libstdc++ problem, our code is correct, and GCC doesn't issue any warning.

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.