mirror of https://github.com/mkerrisk/man-pages
72 lines
2.3 KiB
Groff
72 lines
2.3 KiB
Groff
.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.\" References consulted:
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.\" Linux libc source code
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.\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
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.\" 386BSD man pages
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.\" Modified Sat Jul 24 19:48:17 1993 by Rik Faith (faith@cs.unc.edu)
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.TH DIFFTIME 3 2010-02-25 "GNU" "Linux Programmer's Manual"
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.SH NAME
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difftime \- calculate time difference
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.SH SYNOPSIS
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.nf
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.B #include <time.h>
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.sp
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.BI "double difftime(time_t " time1 ", time_t " time0 );
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.fi
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.SH DESCRIPTION
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The
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.BR difftime ()
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function returns the number of seconds elapsed
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between time \fItime1\fP and time \fItime0\fP, represented as a
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.IR double .
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Each of the times is specified in calendar time, which means its
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value is a measurement (in seconds) relative to the
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Epoch, 1970-01-01 00:00:00 +0000 (UTC).
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.SH "CONFORMING TO"
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SVr4, 4.3BSD, C89, C99.
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.SH NOTES
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On a POSIX system,
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.I time_t
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is an arithmetic type, and one could just
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define
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.RS
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.nf
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#define difftime(t1,t0) (double)(t1 \- t0)
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.fi
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.RE
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when the possible overflow in the subtraction is not a concern.
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On other systems, the data type
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.I time_t
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might use some other encoding
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where subtraction doesn't work directly.
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.SH "SEE ALSO"
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.BR date (1),
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.BR gettimeofday (2),
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.BR time (2),
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.BR ctime (3),
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.BR gmtime (3),
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.BR localtime (3)
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