2004-11-03 13:51:07 +00:00
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.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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2007-06-20 22:33:04 +00:00
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.TH "CLOCK" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
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2004-11-03 13:51:07 +00:00
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.\" clock
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2007-09-20 06:03:25 +00:00
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.SH PROLOG
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This manual page is part of the POSIX Programmer's Manual.
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The Linux implementation of this interface may differ (consult
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the corresponding Linux manual page for details of Linux behavior),
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or the interface may not be implemented on Linux.
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2004-11-03 13:51:07 +00:00
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.SH NAME
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clock \- report CPU time used
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.SH SYNOPSIS
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.LP
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\fB#include <time.h>
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.br
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.sp
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clock_t clock(void);
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.br
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\fP
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.SH DESCRIPTION
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.LP
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The \fIclock\fP() function shall return the implementation's best
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approximation to the processor time used by the process since
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the beginning of an implementation-defined era related only to the
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process invocation.
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.SH RETURN VALUE
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.LP
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To determine the time in seconds, the value returned by \fIclock\fP()
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should be divided by the value of the macro
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CLOCKS_PER_SEC. \ CLOCKS_PER_SEC is defined to be one million in
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\fI<time.h>\fP. If the processor time used is not available or its
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value cannot be
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represented, the function shall return the value ( \fBclock_t\fP)-1.
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.SH ERRORS
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.LP
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No errors are defined.
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.LP
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\fIThe following sections are informative.\fP
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.SH EXAMPLES
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.LP
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None.
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.SH APPLICATION USAGE
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.LP
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In order to measure the time spent in a program, \fIclock\fP() should
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be called at the start of the program and its return
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value subtracted from the value returned by subsequent calls. The
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value returned by \fIclock\fP() is defined for compatibility
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across systems that have clocks with different resolutions. The resolution
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on any particular system need not be to microsecond
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accuracy.
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.LP
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The value returned by \fIclock\fP() may wrap around on some implementations.
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For example, on a machine with 32-bit values for
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\fBclock_t\fP, it wraps after 2147 seconds or 36 minutes.
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.SH RATIONALE
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.LP
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None.
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.SH FUTURE DIRECTIONS
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.LP
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None.
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.SH SEE ALSO
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.LP
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2007-09-20 06:11:55 +00:00
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\fIasctime\fP(), \fIctime\fP(), \fIdifftime\fP(), \fIgmtime\fP()
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2004-11-03 13:51:07 +00:00
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, \fIlocaltime\fP()
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, \fImktime\fP(), \fIstrftime\fP(), \fIstrptime\fP(), \fItime\fP()
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, \fIutime\fP(), the Base
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2004-11-03 13:51:07 +00:00
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Definitions volume of IEEE\ Std\ 1003.1-2001, \fI<time.h>\fP
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.SH COPYRIGHT
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Portions of this text are reprinted and reproduced in electronic form
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from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
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-- Portable Operating System Interface (POSIX), The Open Group Base
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Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
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Electrical and Electronics Engineers, Inc and The Open Group. In the
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event of any discrepancy between this version and the original IEEE and
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The Open Group Standard, the original IEEE and The Open Group Standard
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is the referee document. The original Standard can be obtained online at
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http://www.opengroup.org/unix/online.html .
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