NAME¶

std::chrono::high_resolution_clock - std::chrono::high_resolution_clock

Synopsis¶

Defined in header <chrono>
class high_resolution_clock; (since C++11)

Class std::chrono::high_resolution_clock represents the clock with the smallest tick
period provided by the implementation. It may be an alias of
std::chrono::system_clock or std::chrono::steady_clock, or a third, independent
clock.

std::chrono::high_resolution_clock meets the requirements of TrivialClock.

Member types¶

Member type Definition
rep arithmetic type representing the number of ticks in the clock's duration
period a std::ratio type representing the tick period of the clock, in seconds
duration std::chrono::duration<rep, period>
time_point std::chrono::time_point<std::chrono::high_resolution_clock>

Member constants¶

true if the time between ticks is always constant, i.e.
constexpr bool is_steady calls to now() return values that increase monotonically
[static] even in case of some external clock adjustment, otherwise
false
(public static member constant)

Member functions¶

now returns a std::chrono::time_point representing the current value of the
[static] clock
(public static member function)

Notes¶

There has been some controversy around the use of high_resolution_clock. Howard
Hinnant, who claims to have introduced high_resolution_clock to the language, stated
in 2016 on the ISO C++ Standard - Discussion mailing list that he was in favor of
deprecating it. His rationale was that, because the standard allows for it to be an
alias for std::chrono::steady_clock or std::chrono::system_clock, its use adds
uncertainty to a program without benefit. However, other participants in the thread
spoke out its favor, for instance on the basis that, because neither
std::chrono::steady_clock nor std::chrono::system_clock come with any particular
resolution guarantees, high_resolution_clock serves a useful role by giving the
vendor an opportunity to supply the platform's highest-resolution clock, when
neither its std::chrono::steady_clock nor its std::chrono::system_clock would be
that.

It is often just an alias for std::chrono::steady_clock or
std::chrono::system_clock, but which one it is depends on the library or
configuration. When it is a system_clock, it is not monotonic (e.g., the time can go
backwards). For example, as of 2023, libstdc++ has it aliased to system_clock "until
higher-than-nanosecond definitions become feasible"^[1], MSVC has it as
steady_clock^[2], and libc++ uses steady_clock when the C++ standard library
implementation supports a monotonic clock and system_clock otherwise^[3].

See also¶

system_clock wall clock time from the system-wide realtime clock
(C++11) (class)
steady_clock monotonic clock that will never be adjusted
(C++11) (class)

External links¶

1. ↑ libstdc++ <chrono.h>
2. ↑ msvc high_resolution_clock
3. ↑ libc++ <high_resolution_clock.h>