clock

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 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>

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 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 .



IEEE/The Open Group                   2013                             CLOCK(3P)