CLOCK(3P)                 POSIX Programmer's Manual                CLOCK(3P)

PROLOG         top

       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         top

       clock — report CPU time used

SYNOPSIS         top

       #include <time.h>

       clock_t clock(void);

DESCRIPTION         top

       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         top

       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         top

       No errors are defined.

       The following sections are informative.

EXAMPLES         top



       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         top




SEE ALSO         top

       asctime(3p), ctime(3p), difftime(3p), gmtime(3p), localtime(3p),
       mktime(3p), strftime(3p), strptime(3p), time(3p), utime(3p)

       The Base Definitions volume of POSIX.1‐2008, time.h(0p)

COPYRIGHT         top

       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 .

       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 .

IEEE/The Open Group                 2013                           CLOCK(3P)