id,summary,reporter,owner,description,type,status,milestone,component,version,severity,resolution,keywords,cc
9146,chrono_io support for time format with fractional seconds,Johan Lundberg <lundberj@…>,viboes,"
I propose %f and %F is added to chrono_io in analogy with http://www.boost.org/doc/libs/1_53_0/doc/html/date_time/date_time_io.html 

Unfortunately this is just a specification, no suggested implementation. 

Examples:
{{{
 1970-01-01 00:02:46
 1970-01-01 00:02:46.7
 1970-01-01 00:02:46.67
 1970-01-01 00:02:46.667
}}}
all the way up to nanoseconds (as gnu date +%N):
{{{
 1970-01-01 00:02:46.666666667
}}}

(variants with T instead of space, and time-zone are the real use-cases, but that aspect already works)

Some tools write fractional seconds only if they are not zero. date_time_io supports that using %F so I suggest that for chrono_io as well.

To support writing all of the above formats one could allow for example %3f (and %3F) for printing .667. Alternatively, %N for nanoseconds. When parsing i suggest the number of digits specified is ignored but I may be wrong on that. 

In addition to the above, the documentation has no list of allowed keys for the format strings.

references:

* The bug https://svn.boost.org/trac/boost/ticket/7868 was just fixed. 

* doc: http://www.boost.org/doc/libs/1_54_0/doc/html/chrono/users_guide.html#chrono.users_guide.getting_started.hello_world__ : 

'Unfortunately there are no formatting/parsing sequences which indicate fractional seconds. Boost.Chrono does not provide such sequences. In the meantime, one can format and parse fractional seconds for system_clock::time_point by defaulting the format, or by using an empty string in time_fmt().'

",Feature Requests,closed,Boost 1.55.0,chrono,Boost 1.54.0,Problem,fixed,,