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NAME

       clock - report CPU time used

SYNOPSIS

       #include <time.h>

       clock_t clock(void);

DESCRIPTION

       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 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 .