clock(3) [suse man page]

CLOCK(3)						     Linux Programmer's Manual							  CLOCK(3)

NAME

       clock - Determine processor time

SYNOPSIS

       #include <time.h>

       clock_t clock(void);

DESCRIPTION

       The clock() function returns an approximation of processor time used by the program.

RETURN VALUE

       The value returned is the CPU time used so far as a clock_t; to get the number of seconds used, divide by CLOCKS_PER_SEC.  If the processor
       time used is not available or its value cannot be represented, the function returns the value (clock_t) -1.

CONFORMING TO

       C89, C99, POSIX.1-2001.	POSIX requires that CLOCKS_PER_SEC equals 1000000 independent of the actual resolution.

NOTES

       The C standard allows for arbitrary values at the start of the program; subtract the value returned from a call to clock() at the start	of
       the program to get maximum portability.

       Note  that  the	time  can  wrap  around.   On a 32-bit system where CLOCKS_PER_SEC equals 1000000 this function will return the same value
       approximately every 72 minutes.

       On several other implementations, the value returned by clock() also includes the times of any children whose status has been collected via
       wait(2)	(or  another  wait-type  call).   Linux  does  not include the times of waited-for children in the value returned by clock().  The
       times(2) function, which explicitly returns (separate) information about the caller and its children, may be preferable.

SEE ALSO

       clock_gettime(2), getrusage(2), times(2)

COLOPHON

       This page is part of release 3.25 of the Linux man-pages project.  A description of the project, and information about reporting bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

GNU
								    2008-08-28								  CLOCK(3)

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 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 Technol-
       ogy -- 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)