159 lines
7.0 KiB
HTML
159 lines
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HTML
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<title>chrono::naive::time - Rust</title>
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<p class='location'>Module time</p><div class="block items"><ul><li><a href="#structs">Structs</a></li></ul></div><p class='location'><a href='../../index.html'>chrono</a>::<wbr><a href='../index.html'>naive</a></p><script>window.sidebarCurrent = {name: 'time', ty: 'mod', relpath: '../'};</script><script defer src="../sidebar-items.js"></script>
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<h1 class='fqn'><span class='in-band'>Module <a href='../../index.html'>chrono</a>::<wbr><a href='../index.html'>naive</a>::<wbr><a class="mod" href=''>time</a></span><span class='out-of-band'><span id='render-detail'>
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[<span class='inner'>−</span>]
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</span><a class='srclink' href='../../../src/chrono/naive/time.rs.html#5-1163' title='goto source code'>[src]</a></span></h1>
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<div class='docblock'><p>ISO 8601 time without timezone.</p>
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<h1 id='leap-second-handling' class='section-header'><a href='#leap-second-handling'>Leap Second Handling</a></h1>
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<p>Since 1960s, the manmade atomic clock has been so accurate that
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it is much more accurate than Earth's own motion.
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It became desirable to define the civil time in terms of the atomic clock,
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but that risks the desynchronization of the civil time from Earth.
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To account for this, the designers of the Coordinated Universal Time (UTC)
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made that the UTC should be kept within 0.9 seconds of the observed Earth-bound time.
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When the mean solar day is longer than the ideal (86,400 seconds),
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the error slowly accumulates and it is necessary to add a <strong>leap second</strong>
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to slow the UTC down a bit.
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(We may also remove a second to speed the UTC up a bit, but it never happened.)
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The leap second, if any, follows 23:59:59 of June 30 or December 31 in the UTC.</p>
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<p>Fast forward to the 21st century,
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we have seen 26 leap seconds from January 1972 to December 2015.
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Yes, 26 seconds. Probably you can read this paragraph within 26 seconds.
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But those 26 seconds, and possibly more in the future, are never predictable,
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and whether to add a leap second or not is known only before 6 months.
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Internet-based clocks (via NTP) do account for known leap seconds,
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but the system API normally doesn't (and often can't, with no network connection)
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and there is no reliable way to retrieve leap second information.</p>
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<p>Chrono does not try to accurately implement leap seconds; it is impossible.
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Rather, <strong>it allows for leap seconds but behaves as if there are <em>no other</em> leap seconds.</strong>
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Various time arithmetics will ignore any possible leap second(s)
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except when the operand were actually a leap second.
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The leap second is indicated via fractional seconds more than 1 second,
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so values like <code>NaiveTime::from_hms_milli(23, 56, 4, 1_005)</code> are allowed;
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that value would mean 5ms after the beginning of a leap second following 23:56:04.
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Parsing and formatting will correctly handle times that look like leap seconds,
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and you can then conveniently ignore leap seconds if you are not prepared for them.</p>
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<p>If you cannot tolerate this behavior,
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you must use a separate <code>TimeZone</code> for the International Atomic Time (TAI).
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TAI is like UTC but has no leap seconds, and thus slightly differs from UTC.
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Chrono 0.2 does not provide such implementation, but it is planned for 0.3.</p>
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</div><h2 id='structs' class='section-header'><a href="#structs">Structs</a></h2>
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<table>
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<tr class=' module-item'>
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<td><a class="struct" href="struct.NaiveTime.html"
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title='struct chrono::naive::time::NaiveTime'>NaiveTime</a></td>
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<td class='docblock-short'>
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<p>ISO 8601 time without timezone.
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Allows for the nanosecond precision and optional leap second representation.</p>
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</td>
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