The type denoted by file_clock provides
precisely one of the following two sets of static member functions:
template<class Duration>
static sys_time<see below>
to_sys(const file_time<Duration>&);
template<class Duration>
static file_time<see below>
from_sys(const sys_time<Duration>&);
template<class Duration>
static utc_time<see below>
to_utc(const file_time<Duration>&);
template<class Duration>
static file_time<see below>
from_utc(const utc_time<Duration>&);
These member functions shall provide
time_point conversions
consistent with those specified by
utc_clock,
tai_clock, and
gps_clock.The
Duration of the resultant
time_point
is computed from the
Duration of the input
time_point.