huschi.net

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 clock() function shall return the implementation's best  approxima-
       tion  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 dif-
       ferent 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(), strf-
       time(), strptime(), time(), utime(), the  Base  Definitions  volume  of
       IEEE Std 1003.1-2001, <time.h>
COPYRIGHT
       Portions  of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
       Specifications Issue 6, Copyright (C) 2001-2003  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 http://www.opengroup.org/unix/online.html .

IEEE/The Open Group                  2003                            CLOCK(3P)