mirror of
https://github.com/sigmasternchen/php-doc-en
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8cdc6621f9
- array functions - datetime functions - mbstring functions - strings functions - var functions - xml functions - json functions
158 lines
4.5 KiB
XML
158 lines
4.5 KiB
XML
<?xml version="1.0" encoding="utf-8"?>
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<!-- $Revision$ -->
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<chapter xml:id="datetime.examples" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
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&reftitle.examples;
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<section xml:id="datetime.examples-arithmetic">
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<title>Date/Time Arithmetic</title>
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<para>
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The following examples show some pitfalls of Date/Time arithmetic with regard
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to DST transitions and months having different numbers of days.
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</para>
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<para>
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<example>
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<title>DateTimeImmutable::add/sub add intervals which cover elapsed time</title>
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<simpara>
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Adding PT24H over a DST transition will appear to add 23/25 hours (for
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most timezones).
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</simpara>
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<programlisting role="php">
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<![CDATA[
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<?php
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$dt = new DateTimeImmutable("2015-11-01 00:00:00", new DateTimeZone("America/New_York"));
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echo "Start: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
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$dt = $dt->add(new DateInterval("PT3H"));
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echo "End: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
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?>
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]]>
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</programlisting>
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&example.outputs;
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<screen>
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<![CDATA[
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Start: 2015-11-01 00:00:00 -04:00
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End: 2015-11-01 02:00:00 -05:00
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]]>
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</screen>
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</example>
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</para>
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<para>
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<example>
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<title>DateTimeImmutable::modify and strtotime increment or decrement individual component values</title>
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<simpara>
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Adding +24 hours over a DST transition will add exactly 24 hours as seen in
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the date/time string (unless the start or end time is on a transition
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point).
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</simpara>
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<programlisting role="php">
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<![CDATA[
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<?php
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$dt = new DateTimeImmutable("2015-11-01 00:00:00", new DateTimeZone("America/New_York"));
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echo "Start: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
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$dt = $dt->modify("+24 hours");
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echo "End: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
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?>
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]]>
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</programlisting>
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&example.outputs;
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<screen>
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<![CDATA[
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Start: 2015-11-01 00:00:00 -04:00
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End: 2015-11-02 00:00:00 -05:00
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]]>
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</screen>
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</example>
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</para>
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<para>
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<example>
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<title>Adding or subtracting times can over- or underflow dates</title>
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<simpara>
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Like where January 31st + 1 month will result in March 2nd (leap year) or
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3rd (normal year).
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</simpara>
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<programlisting role="php">
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<![CDATA[
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<?php
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echo "Normal year:\n"; // February has 28 days
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$dt = new DateTimeImmutable("2015-01-31 00:00:00", new DateTimeZone("America/New_York"));
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echo "Start: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
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$dt = $dt->modify("+1 month");
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echo "End: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
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echo "Leap year:\n"; // February has 29 days
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$dt = new DateTimeImmutable("2016-01-31 00:00:00", new DateTimeZone("America/New_York"));
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echo "Start: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
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$dt = $dt->modify("+1 month");
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echo "End: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
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?>
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]]>
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</programlisting>
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&example.outputs;
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<screen>
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<![CDATA[
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Normal year:
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Start: 2015-01-31 00:00:00 -05:00
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End: 2015-03-03 00:00:00 -05:00
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Leap year:
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Start: 2016-01-31 00:00:00 -05:00
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End: 2016-03-02 00:00:00 -05:00
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]]>
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</screen>
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<simpara>
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To get the last day of the next month (i.e. to prevent the overflow),
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the <literal>last day of</literal> format is available.
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</simpara>
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<programlisting role="php">
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<![CDATA[
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<?php
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echo "Normal year:\n"; // February has 28 days
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$dt = new DateTimeImmutable("2015-01-31 00:00:00", new DateTimeZone("America/New_York"));
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echo "Start: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
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$dt = $dt->modify("last day of next month");
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echo "End: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
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echo "Leap year:\n"; // February has 29 days
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$dt = new DateTimeImmutable("2016-01-31 00:00:00", new DateTimeZone("America/New_York"));
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echo "Start: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
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$dt = $dt->modify("last day of next month");
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echo "End: ", $dt->format("Y-m-d H:i:s P"), PHP_EOL;
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?>
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]]>
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</programlisting>
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&example.outputs;
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<screen>
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<![CDATA[
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Normal year:
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Start: 2015-01-31 00:00:00 -05:00
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End: 2015-02-28 00:00:00 -05:00
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Leap year:
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Start: 2016-01-31 00:00:00 -05:00
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End: 2016-02-29 00:00:00 -05:00
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]]>
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</screen>
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</example>
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</para>
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</section>
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</chapter>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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sgml-omittag:t
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sgml-shorttag:t
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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indent-tabs-mode:nil
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sgml-parent-document:nil
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sgml-default-dtd-file:"~/.phpdoc/manual.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:nil
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sgml-local-ecat-files:nil
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End:
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vim600: syn=xml fen fdm=syntax fdl=2 si
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vim: et tw=78 syn=sgml
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vi: ts=1 sw=1
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-->
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