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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.

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 min‐
       utes.

       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)

GNU                                                                            2021-03-22                                                                       CLOCK(3)