NAME

       clock - determine processor time

LIBRARY

       Standard C library (libc, -lc)

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 │
       └───────────────────────────────────────────────────────────────┴───────────────┴─────────┘

VERSIONS

       XSI requires that CLOCKS_PER_SEC equals 1000000 independent of the actual resolution.

       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.

STANDARDS

       C11, POSIX.1-2008.

HISTORY

       POSIX.1-2001, C89.

       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).

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.

SEE ALSO

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