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dc36d6f9bb
Remove ancient SCCS tags from the tree, automated scripting, with two minor fixup to keep things compiling. All the common forms in the tree were removed with a perl script. Sponsored by: Netflix
140 lines
3.7 KiB
Groff
140 lines
3.7 KiB
Groff
.\" Copyright (c) 1989, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" the American National Standards Committee X3, on Information
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.\" Processing Systems.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.Dd April 14, 2022
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.Dt TIME 3
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.Os
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.Sh NAME
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.Nm time
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.Nd get time of day
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In time.h
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.Ft time_t
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.Fn time "time_t *tloc"
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.Sh DESCRIPTION
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The
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.Fn time
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function
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returns the value of time in seconds since 0 hours, 0 minutes,
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0 seconds, January 1, 1970, Coordinated Universal Time (UTC).
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If an error occurs,
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.Fn time
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returns the value
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.Po Vt time_t Pc Ns \-1 .
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.Pp
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The return value is also stored in
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.No \&* Ns Va tloc ,
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provided that
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.Va tloc
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is non-null.
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.Sh ERRORS
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The
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.Fn time
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function may fail for any of the reasons described in
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.Xr clock_gettime 2 .
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.Sh SEE ALSO
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.Xr clock_gettime 2 ,
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.Xr gettimeofday 2 ,
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.Xr ctime 3
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.Sh STANDARDS
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The
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.Nm
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function conforms to
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.St -p1003.1-2008 .
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.Sh HISTORY
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The
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.Fn time
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system call first appeared in
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.At v1 .
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Through the
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.At v3 ,
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it returned 60 Hz ticks since an epoch that changed occasionally, because it
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was a 32-bit value that overflowed in a little over 2 years.
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.Pp
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In
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.At v4
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the granularity of the return value was reduced to whole seconds,
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delaying the aforementioned overflow until 2038.
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.Pp
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.At v7
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introduced the
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.Fn ftime
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system call, which returned time at a millisecond level,
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though retained the
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.Fn gtime
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system call (exposed as
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.Fn time
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in userland).
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.Fn time
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could have been implemented as a wrapper around
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.Fn ftime ,
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but that wasn't done.
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.Pp
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.Bx 4.1c
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implemented a higher-precision time function
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.Fn gettimeofday
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to replace
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.Fn ftime
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and reimplemented
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.Fn time
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in terms of that.
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.Pp
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Since
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.Fx 9
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the implementation of
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.Fn time
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uses
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.Fn clock_gettime "CLOCK_SECOND"
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instead of
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.Fn gettimeofday
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for performance reasons.
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.Sh BUGS
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Neither
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.St -isoC-99
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nor
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.St -p1003.1-2001
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requires
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.Fn time
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to set
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.Va errno
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on failure; thus, it is impossible for an application to distinguish
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the valid time value \-1 (representing the last UTC second of 1969)
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from the error return value.
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.Pp
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Systems conforming to earlier versions of the C and POSIX
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standards (including older versions of
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.Fx )
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did not set
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.No \&* Ns Va tloc
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in the error case.
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