clock(3p) [posix man page]

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 correspond-
       ing 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 Technol-
       ogy -- 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 Stan-
       dard 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)