1CLOCK(3)                   Linux Programmer's Manual                  CLOCK(3)
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NAME

6       clock - determine processor time
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SYNOPSIS

9       #include <time.h>
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11       clock_t clock(void);
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DESCRIPTION

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

18       The value returned is the CPU time used so far as a clock_t; to get the
19       number  of  seconds  used,  divide by CLOCKS_PER_SEC.  If the processor
20       time used is not available or its  value  cannot  be  represented,  the
21       function returns the value (clock_t) -1.
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ATTRIBUTES

24       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
25       tributes(7).
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27       ┌────────────────────────────────────────────┬───────────────┬─────────┐
28       │Interface                                   │ Attribute     │ Value   │
29       ├────────────────────────────────────────────┼───────────────┼─────────┤
30       │clock()                                     │ Thread safety │ MT-Safe │
31       └────────────────────────────────────────────┴───────────────┴─────────┘
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CONFORMING TO

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

38       The C standard allows for arbitrary values at the start of the program;
39       subtract the value returned from a call to clock() at the start of  the
40       program to get maximum portability.
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42       Note  that  the  time  can  wrap  around.   On  a  32-bit  system where
43       CLOCKS_PER_SEC equals 1000000 this function will return the same  value
44       approximately every 72 minutes.
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46       On  several  other  implementations, the value returned by clock() also
47       includes the times of any children whose status has been collected  via
48       wait(2)  (or another wait-type call).  Linux does not include the times
49       of waited-for children in the value returned by clock().  The  times(2)
50       function,  which  explicitly  returns  (separate) information about the
51       caller and its children, may be preferable.
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53       In glibc 2.17 and earlier, clock() was implemented on top of  times(2).
54       For  improved  accuracy,  since glibc 2.18, it is implemented on top of
55       clock_gettime(2) (using the CLOCK_PROCESS_CPUTIME_ID clock).
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SEE ALSO

58       clock_gettime(2), getrusage(2), times(2)
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COLOPHON

61       This page is part of release 5.12 of the Linux  man-pages  project.   A
62       description  of  the project, information about reporting bugs, and the
63       latest    version    of    this    page,    can     be     found     at
64       https://www.kernel.org/doc/man-pages/.
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68GNU                               2021-03-22                          CLOCK(3)
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