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.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).
       ┌───────────┬───────────────┬─────────┐
       │ Interface │ Attribute     │ Value   │
       ├───────────┼───────────────┼─────────┤
       │ clock()   │ Thread safety │ MT-Safe │
       └───────────┴───────────────┴─────────┘

CONFORMING TO

       POSIX.1-2001, POSIX.1-2008, C89, C99.  XSI 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  accuracy,  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  5.10  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
       https://www.kernel.org/doc/man-pages/.

GNU                                                2017-09-15                                           CLOCK(3)