1CLOCK(P)                   POSIX Programmer's Manual                  CLOCK(P)
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NAME

6       clock - report CPU time used
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SYNOPSIS

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

15       The  clock() function shall return the implementation's best approxima‐
16       tion to the processor time used by the process since the  beginning  of
17       an implementation-defined era related only to the process invocation.
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RETURN VALUE

20       To  determine the time in seconds, the value returned by clock() should
21       be divided by the value of the macro CLOCKS_PER_SEC.     CLOCKS_PER_SEC
22       is  defined  to be one million in <time.h>.  If the processor time used
23       is not available or its value cannot be represented, the function shall
24       return the value ( clock_t)-1.
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ERRORS

27       No errors are defined.
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29       The following sections are informative.
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EXAMPLES

32       None.
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APPLICATION USAGE

35       In  order  to  measure  the  time spent in a program, clock() should be
36       called at the start of the program and its return value subtracted from
37       the  value  returned by subsequent calls. The value returned by clock()
38       is defined for compatibility across systems that have clocks with  dif‐
39       ferent resolutions. The resolution on any particular system need not be
40       to microsecond accuracy.
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42       The value returned by clock() may wrap around on some  implementations.
43       For  example,  on  a  machine  with 32-bit values for clock_t, it wraps
44       after 2147 seconds or 36 minutes.
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RATIONALE

47       None.
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FUTURE DIRECTIONS

50       None.
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SEE ALSO

53       asctime() , ctime() , difftime() , gmtime() , localtime() , mktime()  ,
54       strftime()  , strptime() , time() , utime() , the Base Definitions vol‐
55       ume of IEEE Std 1003.1-2001, <time.h>
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58       Portions of this text are reprinted and reproduced in  electronic  form
59       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
60       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
61       Specifications  Issue  6,  Copyright  (C) 2001-2003 by the Institute of
62       Electrical and Electronics Engineers, Inc and The Open  Group.  In  the
63       event of any discrepancy between this version and the original IEEE and
64       The Open Group Standard, the original IEEE and The Open Group  Standard
65       is  the  referee document. The original Standard can be obtained online
66       at http://www.opengroup.org/unix/online.html .
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70IEEE/The Open Group                  2003                             CLOCK(P)
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