Chrono V2 IO - format tags 'unsupported'?

[steve.hickman@…]

http://www.boost.org/doc/libs/1_59_0/doc/html/chrono/reference.html#chrono.reference.io.ios_state_hpp.sag.set_time_fmt

table 6.3 on the page linked above describes format tags to be used with IO. Several are listed as unsupported. There is no explanation of what 'unsupported' means. Does it mean a format string with one of those tags will cause an exception? Will the format tag be ignored? Will the entire format string fail to work? Will interation over the string stop before or after the 'unsupported' tag? More explanation would be helpful here.

[viboes]

In http://www.boost.org/doc/libs/1_59_0/doc/html/chrono.html you can find the reference to the recomendation on which these tags arebased.

"

system_clock::time_point I/O is proposed in terms of UTC timepoints, strongly guided by ISO 9899:1999, Programming languages - C, ISO 9945:2003, Information Technology - Portable Operating System Interface (POSIX) and ISO 8601:2004, Data elements and interchange formats - Information interchange - Representation of dates and times.

"

By not supported I mean that it is not a valid tag and so it will result on an error (std::ios_base::failbit) as any standard IO operation does. It works as the std::time_get facet. It could add this if this is of any help to you. I expected that the user was aware of how standard IO facilities work.