1CLOCK(3P)                  POSIX Programmer's Manual                 CLOCK(3P)
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PROLOG

6       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
7       implementation of this interface may differ (consult the  corresponding
8       Linux  manual page for details of Linux behavior), or the interface may
9       not be implemented on Linux.
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NAME

12       clock - report CPU time used
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SYNOPSIS

15       #include <time.h>
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17       clock_t clock(void);
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DESCRIPTION

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

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

33       No errors are defined.
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35       The following sections are informative.
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EXAMPLES

38       None.
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APPLICATION USAGE

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

53       None.
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FUTURE DIRECTIONS

56       None.
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SEE ALSO

59       asctime(),  ctime(), difftime(), gmtime(), localtime(), mktime(), strf‐
60       time(), strptime(), time(), utime(), the  Base  Definitions  volume  of
61       IEEE Std 1003.1-2001, <time.h>
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64       Portions  of  this text are reprinted and reproduced in electronic form
65       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
66       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
67       Specifications Issue 6, Copyright (C) 2001-2003  by  the  Institute  of
68       Electrical  and  Electronics  Engineers, Inc and The Open Group. In the
69       event of any discrepancy between this version and the original IEEE and
70       The  Open Group Standard, the original IEEE and The Open Group Standard
71       is the referee document. The original Standard can be  obtained  online
72       at http://www.opengroup.org/unix/online.html .
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76IEEE/The Open Group                  2003                            CLOCK(3P)
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