bionic (3) clock.3posix.gz

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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 approximation 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 different 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(), strftime(), strptime(), time(), utime()

       The Base Definitions volume of POSIX.1‐2008, <time.h>


       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 Electrical 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.kernel.org/doc/man-pages/reporting_bugs.html .