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.

       In glibc 2.17 and earlier, clock() was implemented on top of times(2).  For improved accu‐
       racy,  since  glibc  2.18,  it  is  implemented  on  top  of  clock_gettime(2)  (using the
       CLOCK_PROCESS_CPUTIME_ID clock).

SEE ALSO
       clock_gettime(2), getrusage(2), times(2)

COLOPHON
       This page is part of release 3.74 of the Linux man-pages project.  A  description  of  the
       project,  information  about  reporting  bugs, and the latest version of this page, can be
       found at http://www.kernel.org/doc/man-pages/.



GNU                                         2014-09-21                                   CLOCK(3)