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

       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.

       clock — report CPU time used

       #include <time.h>

       clock_t clock(void);

       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.1‐2017 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.

       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.

       No errors are defined.

       The following sections are informative.


       In programming environments where clock_t is a 32-bit integer type and
       CLOCKS_PER_SEC is one million, clock() will start failing in less than 36
       minutes of processor time for signed clock_t, or 72 minutes for unsigned
       clock_t.  Applications intended to be portable to such environments
       should use times() instead (or clock_gettime() with
       CLOCK_PROCESS_CPUTIME_ID, if supported).

       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.



       asctime(), clock_getres(), ctime(), difftime(), gmtime(), localtime(),
       mktime(), strftime(), strptime(), time(), times(), utime()

       The Base Definitions volume of POSIX.1‐2017, <time.h>

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute
       of Electrical and Electronics Engineers, Inc and The Open Group.  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                   2017                             CLOCK(3P)