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       clock - determine processor time


       #include <time.h>

       clock_t clock(void);


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


       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.


       For an explanation of the terms used in this section, see attributes(7).

       │InterfaceAttributeValue   │
       │clock()                                                        │ Thread safety │ MT-Safe │


       POSIX.1-2001,  POSIX.1-2008,  C89,  C99.   XSI requires that CLOCKS_PER_SEC equals 1000000
       independent of the actual resolution.


       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_gettime(2), getrusage(2), times(2)


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