The Open Group Base Specifications Issue 7
IEEE Std 1003.1-2008, 2016 Edition
Copyright © 2001-2016 The IEEE and The Open Group

#### NAME

> sys/time.h - time types

#### SYNOPSIS

> `[XSI] #include <sys/time.h>`

#### DESCRIPTION

> The <sys/time.h> header shall define the timeval structure, which shall include at least the following members:

>     time_t         tv_sec      Seconds.
>     suseconds_t    tv_usec     Microseconds.

> [OB] The <sys/time.h> header shall define the itimerval structure, which shall include at least the following members:

>     struct timeval it_interval Timer interval.
>     struct timeval it_value    Current value.

> The <sys/time.h> header shall define the time_t and suseconds_t types as described in <sys/types.h>.

> The <sys/time.h> header shall define the fd_set type as described in <sys/select.h>.

> [OB] The <sys/time.h> header shall define the following symbolic constants for the which argument of getitimer() and setitimer():

> ITIMER_REAL
>   Decrements in real time.
> ITIMER_VIRTUAL
>   Decrements in process virtual time.
> ITIMER_PROF
>   Decrements both in process virtual time and when the system is running on behalf of the process.

> The <sys/time.h> header shall define the following as described in <sys/select.h>: FD_CLR() FD_ISSET() FD_SET() FD_ZERO() FD_SETSIZE

> The following shall be declared as functions and may also be defined as macros. Function prototypes shall be provided.

>     [OB]
>     int   getitimer(int, struct itimerval *);
>     int   gettimeofday(struct timeval *restrict, void *restrict);
>     int   setitimer(int, const struct itimerval *restrict,
>               struct itimerval *restrict);

>     int   select(int, fd_set *restrict, fd_set *restrict, fd_set *restrict,
>               struct timeval *restrict);
>     int   utimes(const char *, const struct timeval [2]);

> Inclusion of the <sys/time.h> header may make visible all symbols from the <sys/select.h> header.

The following sections are informative.

#### APPLICATION USAGE

> None.

#### RATIONALE

> None.

#### FUTURE DIRECTIONS

> None.

#### SEE ALSO

> <sys/select.h>, <sys/types.h>

> XSH futimens, getitimer, gettimeofday, pselect

#### CHANGE HISTORY

> First released in Issue 4, Version 2.

#### Issue 5

> The type of tv_usec is changed from long to suseconds_t.

#### Issue 6

> The restrict keyword is added to the prototypes for gettimeofday(), select(), and setitimer().

> The note is added that inclusion of this header may also make symbols visible from <sys/select.h>.

> The utimes() function is marked LEGACY.

#### Issue 7

> This reference page is clarified with respect to macros and symbolic constants.

End of informative text.

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