<xiosbase>: Non-conforming extension ios_base::hexfloat

[frederick-vs-ja]

Describe the bug

MSVC STL provides ios_base::hexfloat, which is probably non-conforming.

STL/stl/inc/xiosbase

Line 47 in 8ddf4da

static constexpr _Fmtflags hexfloat = static_cast<_Fmtflags>(0x3000); // added with TR1 (not in C++11)

And the comment seems wrong as ios_base::hexfloat is not a part of TR1. It was stated in the final draft of TR1 (WG21-N1836) that:

[Note: Adding the format flag hexfloat to class ios_base cannot be done without invading namespace std, so only the named manipulator is provided. Note also that the more obvious use of ios_base::hex to specify hexadecimal floating-point format would change the meaning of existing well defined programs. C++2003 gives no meaning to the combination of fixed and scientific. —end note]

Should we remove it (maybe in vNext) or make it conforming with an LWG issue or a paper?

[strega-nil-ms]

Yeah this is certainly a vNext kind of thing.