27 Time library [time]

27.7 Clocks [time.clock]

27.7.5 Type file_­clock [time.clock.file] Overview [time.clock.file.overview]

namespace std::chrono {
  using file_clock = see below;
file_­clock is an alias for a type meeting the Cpp17TrivialClock requirements ([time.clock.req]), and using a signed arithmetic type for file_­clock​::​rep.
file_­clock is used to create the time_­point system used for file_­time_­type ([filesystems]).
Its epoch is unspecified, and noexcept(file_­clock​::​now()) is true.
The type that file_­clock denotes may be in a different namespace than std​::​chrono, such as std​::​filesystem.
— end note