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.\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\" License.
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.\" Modified Sat Jul 24 21:27:01 1993 by Rik Faith (faith@cs.unc.edu)
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2007-09-20 06:52:22 +00:00
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.\" Modified 14 Jun 2002, Michael Kerrisk <mtk.manpages@gmail.com>
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intro.1, time.1, accept.2, bind.2, connect.2, execve.2, flock.2, getdents.2, getpriority.2, getuid.2, intro.2, ioctl.2, mincore.2, mknod.2, personality.2, ptrace.2, read.2, recv.2, select_tut.2, send.2, sendfile.2, shmctl.2, sigaction.2, signal.2, stat.2, times.2, truncate.2, umask.2, wait.2, MB_CUR_MAX.3, MB_LEN_MAX.3, argz_add.3, btowc.3, clearenv.3, clock.3, cmsg.3, end.3, endian.3, errno.3, exit.3, fgetwc.3, fgetws.3, fopen.3, fputwc.3, fputws.3, fseek.3, fwide.3, getfsent.3, getgrnam.3, gethostid.3, getipnodebyname.3, getmntent.3, getpwnam.3, getwchar.3, grantpt.3, iconv.3, iconv_close.3, iconv_open.3, insque.3, intro.3, iswalnum.3, iswalpha.3, iswblank.3, iswcntrl.3, iswctype.3, iswdigit.3, iswgraph.3, iswlower.3, iswprint.3, iswpunct.3, iswspace.3, iswupper.3, iswxdigit.3, malloc.3, mblen.3, mbrlen.3, mbrtowc.3, mbsinit.3, mbsnrtowcs.3, mbsrtowcs.3, mbstowcs.3, mbtowc.3, mkstemp.3, mktemp.3, nl_langinfo.3, openpty.3, posix_openpt.3, printf.3, ptsname.3, putwchar.3, qecvt.3, rcmd.3, readdir.3, rexec.3, rpc.3, setnetgrent.3, shm_open.3, sigpause.3, stdin.3, stpcpy.3, strftime.3, strptime.3, syslog.3, towctrans.3, towlower.3, towupper.3, ttyslot.3, ungetwc.3, unlocked_stdio.3, wcpcpy.3, wcpncpy.3, wcrtomb.3, wcscasecmp.3, wcscat.3, wcschr.3, wcscmp.3, wcscpy.3, wcscspn.3, wcsdup.3, wcslen.3, wcsncasecmp.3, wcsncat.3, wcsncmp.3, wcsncpy.3, wcsnlen.3, wcsnrtombs.3, wcspbrk.3, wcsrchr.3, wcsrtombs.3, wcsspn.3, wcsstr.3, wcstok.3, wcstombs.3, wcswidth.3, wctob.3, wctomb.3, wctrans.3, wctype.3, wcwidth.3, wmemchr.3, wmemcmp.3, wmemcpy.3, wmemmove.3, wmemset.3, wprintf.3, console_ioctl.4, pts.4, elf.5, filesystems.5, hosts.5, proc.5, ttytype.5, boot.7, capabilities.7, credentials.7, epoll.7, glob.7, koi8-r.7, path_resolution.7, pty.7, signal.7, suffixes.7, time.7, unicode.7, unix.7, uri.7, utf-8.7: global fix: s/Unix/UNIX/
The man pages were rather inconsistent in the use of "Unix"
versus "UNIX". Let's go with the trademark usage.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
2010-10-12 04:45:38 +00:00
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.\" Added notes on differences from other UNIX systems with respect to
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.\" waited-for children.
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2008-08-28 11:13:21 +00:00
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.TH CLOCK 3 2008-08-28 "GNU" "Linux Programmer's Manual"
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.SH NAME
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clock \- Determine processor time
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.SH SYNOPSIS
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.nf
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.B #include <time.h>
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.sp
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.B clock_t clock(void);
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.fi
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.SH DESCRIPTION
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The
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.BR clock ()
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function returns an approximation of processor time used by the program.
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.SH "RETURN VALUE"
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The value returned is the CPU time used so far as a
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.IR clock_t ;
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to get the number of seconds used, divide by
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.BR CLOCKS_PER_SEC .
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If the processor time used is not available or its value cannot
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be represented, the function returns the value
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.IR (clock_t)\ \-1 .
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.SH "CONFORMING TO"
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C89, C99, POSIX.1-2001.
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POSIX requires that
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.B CLOCKS_PER_SEC
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equals 1000000 independent
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of the actual resolution.
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.SH NOTES
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The C standard allows for arbitrary values at the start of the program;
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subtract the value returned from a call to
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.BR clock ()
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at the start of the program to get maximum portability.
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.PP
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Note that the time can wrap around.
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On a 32-bit system where
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.B CLOCKS_PER_SEC
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equals 1000000 this function will return the same
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value approximately every 72 minutes.
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.PP
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On several other implementations,
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the value returned by
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.BR clock ()
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also includes the times of any children whose status has been
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collected via
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.BR wait (2)
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(or another wait-type call).
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Linux does not include the times of waited-for children in the
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value returned by
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.BR clock ().
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2007-06-08 09:56:56 +00:00
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.\" I have seen this behavior on Irix 6.3, and the OSF/1, HP/UX, and
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.\" Solaris manual pages say that clock() also does this on those systems.
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.\" POSIX.1-2001 doesn't explicitly allow this, nor is there an
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.\" explicit prohibition. -- MTK
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The
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.BR times (2)
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function, which explicitly returns (separate) information about the
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caller and its children, may be preferable.
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.SH "SEE ALSO"
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clock_nanosleep.2, getrusage.2, timerfd_create.2, clock.3, clock_getcpuclockid.3, ftime.3, pthread_create.3, pthread_getcpuclockid.3, pthread_tryjoin_np.3, sem_wait.3, time.7: Global fix: Fix xrefs to clock_*.? pages to reflect move to section 2
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
2009-02-07 21:10:39 +00:00
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.BR clock_gettime (2),
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.BR getrusage (2),
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clock_nanosleep.2, getrusage.2, timerfd_create.2, clock.3, clock_getcpuclockid.3, ftime.3, pthread_create.3, pthread_getcpuclockid.3, pthread_tryjoin_np.3, sem_wait.3, time.7: Global fix: Fix xrefs to clock_*.? pages to reflect move to section 2
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
2009-02-07 21:10:39 +00:00
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.BR times (2)
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