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CLOCK(3P)                  POSIX Programmer's Manual                 CLOCK(3P)
PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the  corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.
NAME
       clock -- report CPU time used
SYNOPSIS
       #include <time.h>
       clock_t clock(void);
DESCRIPTION
       The functionality described on this reference page is aligned with  the
       ISO C  standard.  Any  conflict between the requirements described here
       and the ISO C standard is unintentional. This  volume  of  POSIX.1-2008
       defers to the ISO C standard.
       The  clock() function shall return the implementation's best approxima-
       tion to the processor time used by the process since the  beginning  of
       an implementation-defined era related only to the process invocation.
RETURN VALUE
       To  determine the time in seconds, the value returned by clock() should
       be divided by the value of the macro CLOCKS_PER_SEC.  CLOCKS_PER_SEC is
       defined  to  be one million in <time.h>.  If the processor time used is
       not available or its value cannot be represented,  the  function  shall
       return the value (clock_t)-1.
ERRORS
       No errors are defined.
       The following sections are informative.
EXAMPLES
       None.
APPLICATION USAGE
       In  order  to  measure  the  time spent in a program, clock() should be
       called at the start of the program and its return value subtracted from
       the  value  returned by subsequent calls. The value returned by clock()
       is defined for compatibility across systems that have clocks with  dif-
       ferent resolutions. The resolution on any particular system need not be
       to microsecond accuracy.
       The value returned by clock() may wrap around on some  implementations.
       For  example,  on  a  machine  with 32-bit values for clock_t, it wraps
       after 2147 seconds or 36 minutes.
RATIONALE
       None.
FUTURE DIRECTIONS
       None.
SEE ALSO
       asctime(), ctime(), difftime(), gmtime(), localtime(), mktime(),  strf-
       time(), strptime(), time(), utime()
       The Base Definitions volume of POSIX.1-2008, <time.h>
COPYRIGHT
       Portions  of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
       cal  and  Electronics  Engineers,  Inc  and  The  Open Group.  (This is
       POSIX.1-2008 with the 2013 Technical Corrigendum  1  applied.)  In  the
       event of any discrepancy between this version and the original IEEE and
       The Open Group Standard, the original IEEE and The Open Group  Standard
       is  the  referee document. The original Standard can be obtained online
       at http://www.unix.org/online.html .
       Any typographical or formatting errors that appear  in  this  page  are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors,  see  https://www.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                            CLOCK(3P)