clock(3) [freebsd man page]

CLOCK(3)						   BSD Library Functions Manual 						  CLOCK(3)

NAME

     clock -- determine processor time used

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <time.h>

     clock_t
     clock(void);

DESCRIPTION

     The clock() function determines the amount of processor time used since the invocation of the calling process, measured in CLOCKS_PER_SECs of
     a second.

RETURN VALUES

     The clock() function returns the amount of time used unless an error occurs, in which case the return value is -1.

SEE ALSO

     getrusage(2), clocks(7)

STANDARDS

     The clock() function conforms to ISO/IEC 9899:1990 (``ISO C90'').	However, Version 2 of the Single UNIX Specification (``SUSv2'') requires
     CLOCKS_PER_SEC to be defined as one million.  FreeBSD does not conform to this requirement; changing the value would introduce binary incom-
     patibility and one million is still inadequate on modern processors.

BSD
								   June 4, 1993 							       BSD

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 3.44 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)