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.Dd January 12, 2025
.Dt TIME.H 3HEAD
.Os
.Sh NAME
.Nm time.h ,
.Nm time
.Nd time types
.Sh SYNOPSIS
.In time.h
.Sh DESCRIPTION
The
.In time.h
header declares the structure
.Vt tm ,
which includes the following members:
.Bd -literal -offset indent
int tm_sec     /* seconds [0,60] */
int tm_min     /* minutes [0,59] */
int tm_hour    /* hour [0,23] */
int tm_mday    /* day of month [1,31] */
int tm_mon     /* month of year [0,11] */
int tm_year    /* years since 1900 */
int tm_wday    /* day of week [0,6] (Sunday =0) */
int tm_yday    /* day of year [0,365] */
int tm_isdst   /* daylight savings flag */
.Ed
.Pp
The value of
.Fa tm_isdst
is positive if Daylight Saving Time is in effect, 0 if Daylight Saving
Time is not in effect, and negative if the information is not available.
.Pp
The
.In time.h
header defines the following symbolic names:
.Bl -tag -width Ds
.It Dv CLOCK_MONOTONIC
The identifier for the system-wide monotonic clock, which is defined as a clock
whose value cannot be set with
.Fn clock_settime
and that cannot have backward clock jumps.
The maximum possible clock jump is implementation-defined.
See
.Xr clock_settime 3C .
.It Dv CLOCKS_PER_SEC
A number used to convert the value returned by the
.Fn clock
function into seconds.
See
.Xr clock 3C .
.It Dv CLOCK_PROCESS_CPUTIME_ID
The identifier of the CPU-time clock associated with the process making a
.Fn clock
or
.Fn timer_*
function call.
This clock includes both user and system CPU-time.
.It Dv CLOCK_REALTIME
The identifier of the system-wide realtime clock.
.It Dv CLOCK_THREAD_CPUTIME_ID
The identifier of the CPU-time clock associated with the thread making a
.Fn clock
or
.Fn timer_*
function call.
This clock includes both user and system CPU-time.
.It Dv CLOCK_VIRTUAL
The identifier of the CPU-time clock associated with the thread making a
.Fn clock
or
.Fn timer_*
function call.
This clock only includes user CPU-time.
.It Dv NULL
Null pointer constant.
.It Dv TIMER_ABSTIME
Flag indicating time is absolute.
For functions taking timer objects, this refers to the clock associated
with the timer.
.El
.Pp
The
.In time.h
header defines the following clock constants which are used with the
.Xr timespec_get 3C
and
.Xr timespec_getres 3C
calls.
Each one has a
.Dv CLOCK_*
equivalent.
.Bl -tag -width Ds
.It Dv TIME_UTC
The equivalent of
.Dv CLOCK_REALTIME .
.It Dv TIME_MONOTONIC
The equivalent of
.Dv CLOCK_HIGHRES .
.It Dv TIME_ACTIVE
The equivalent of
.Dv CLOCK_PROCESS_CPUTIME_ID .
.It Dv TIME_THREAD_ACTIVE
The equivalent of
.Dv CLOCK_THREAD_CPUTIME_ID .
.It Dv TIME_THREAD_ACTIVE_USR
The equivalent of
.Dv CLOCK_VIRTUAL .
.El
.Pp
The
.In time.h
header declares the
.Vt timespec
structure, which has the following members:
.Bd -literal -offset indent
time_t tv_sec     /* seconds */
long   tv_nsec     /* nanoseconds */
.Ed
.Pp
The
.In time.h
header declares the
.Vt itimerspec
structure, which has the following members:
.Bd -literal -offset indent
struct timespec it_interval     /* timer period */
struct timespec it_value     /* timer expiration */
.Ed
.Pp
The
.Vt clock_t ,
.Vt size_t ,
.Vt time_t ,
.Vt clockid_t ,
and
.Vt timer_t
types are defined as described in
.In sys/types.h .
See
.Xr types.h 3HEAD .
.Pp
Although the value of
.Dv CLOCKS_PER_SEC
is required to be 1 million on all standard-conforming systems, it can
be variable on other systems, and it should not be assumed that
.Dv CLOCKS_PER_SEC
is a compile-time constant.
.Pp
The
.In time.h
header provides a declaration for
.Dv getdate_err .
.Pp
The following are declared as variables:
.Bd -literal -offset indent
extern int daylight;
extern long timezone;
extern char *tzname[];
.Ed
.Pp
Inclusion of the
.In time.h
header can make visible all symbols from the
.In signal.h
header.
.Sh USAGE
The range [0,60] for
.Fa tm_sec
allows for the occasional leap second.
.Pp
.Fa tm_year
is a signed value; therefore, years before 1900 can be represented.
.Pp
To obtain the number of clock ticks per second returned by the
.Fn times
function, applications should call
.Fn sysconf "_SC_CLK_TCK" .
See
.Xr times 2
and
.Xr sysconf 3C .
.Sh INTERFACE STABILITY
.Sy Committed
.Sh SEE ALSO
.Xr time 2 ,
.Xr utime 2 ,
.Xr clock 3C ,
.Xr clock_settime 3C ,
.Xr ctime 3C ,
.Xr difftime 3C ,
.Xr getdate 3C ,
.Xr mktime 3C ,
.Xr nanosleep 3C ,
.Xr strftime 3C ,
.Xr strptime 3C ,
.Xr timer_create 3C ,
.Xr timer_delete 3C ,
.Xr timer_settime 3C ,
.Xr timespec_get 3C ,
.Xr types.h 3HEAD ,
.Xr attributes 7 ,
.Xr standards 7