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<refentry xml:id="datetime.diff" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
 <refnamediv>
  <refname>DateTimeInterface::diff</refname>
  <refname>DateTimeImmutable::diff</refname>
  <refname>DateTime::diff</refname>
  <refname>date_diff</refname>
  <refpurpose>Returns the difference between two DateTime objects</refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <para>&style.oop;</para>
  <methodsynopsis role="DateTimeInterface">
   <modifier>public</modifier> <type>DateInterval</type><methodname>DateTimeInterface::diff</methodname>
   <methodparam><type>DateTimeInterface</type><parameter>targetObject</parameter></methodparam>
   <methodparam choice="opt"><type>bool</type><parameter>absolute</parameter><initializer>&false;</initializer></methodparam>
  </methodsynopsis>
  <methodsynopsis role="DateTimeImmutable">
   <modifier>public</modifier> <type>DateInterval</type><methodname>DateTimeImmutable::diff</methodname>
   <methodparam><type>DateTimeInterface</type><parameter>targetObject</parameter></methodparam>
   <methodparam choice="opt"><type>bool</type><parameter>absolute</parameter><initializer>&false;</initializer></methodparam>
  </methodsynopsis>
  <methodsynopsis role="DateTime">
   <modifier>public</modifier> <type>DateInterval</type><methodname>DateTime::diff</methodname>
   <methodparam><type>DateTimeInterface</type><parameter>targetObject</parameter></methodparam>
   <methodparam choice="opt"><type>bool</type><parameter>absolute</parameter><initializer>&false;</initializer></methodparam>
  </methodsynopsis>
  <para>&style.procedural;</para>
  <methodsynopsis>
   <type>DateInterval</type><methodname>date_diff</methodname>
   <methodparam><type>DateTimeInterface</type><parameter>baseObject</parameter></methodparam>
   <methodparam><type>DateTimeInterface</type><parameter>targetObject</parameter></methodparam>
   <methodparam choice="opt"><type>bool</type><parameter>absolute</parameter><initializer>&false;</initializer></methodparam>
  </methodsynopsis>
  <para>
   Returns the difference between two <classname>DateTimeInterface</classname>
   objects.
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <variablelist>
   <varlistentry>
    <term><parameter>datetime</parameter></term>
    <listitem>
     <para>
      The date to compare to.
     </para>
    </listitem>
   </varlistentry>
   <varlistentry>
    <term><parameter>absolute</parameter></term>
    <listitem>
     <para>
      Should the interval be forced to be positive?
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   The <classname>DateInterval</classname> object represents the
   difference between the two dates.
  </para>
  <para>
   The <parameter>absolute</parameter> parameter only affects the
   <parameter>invert</parameter> property of a
   <classname>DateInterval</classname> object.
  </para>
  <para>
   The return value more specifically represents the clock-time interval to
   apply to the original object (<parameter>$this</parameter> or
   <parameter>$originObject</parameter>) to arrive at the
   <parameter>$targetObject</parameter>. This process is not always
   reversible.
  </para>
  <para>
   The method is aware of DST changeovers, and hence can return an interval of
   <literal>24 hours and 30 minutes</literal>, as per one of the examples. If
   you want to calculate with absolute time, you need to convert both the
   <parameter>$this</parameter>/<parameter>$baseObject</parameter>, and
   <parameter>$targetObject</parameter> to UTC first.
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <example>
   <title><function>DateTimeImmutable::diff</function> example</title>
   <para>&style.oop;</para>
   <programlisting role="php">
<![CDATA[
<?php
$origin = new DateTimeImmutable('2009-10-11');
$target = new DateTimeImmutable('2009-10-13');
$interval = $origin->diff($target);
echo $interval->format('%R%a days');
?>
]]>
   </programlisting>
   <para>&style.procedural;</para>
   <programlisting role="php">
<![CDATA[
<?php
$origin = date_create('2009-10-11');
$target = date_create('2009-10-13');
$interval = date_diff($origin, $target);
echo $interval->format('%R%a days');
?>
]]>
   </programlisting>
   &examples.outputs;
   <screen>
<![CDATA[
+2 days
]]>
   </screen>
  </example>

  <example>
   <title><methodname>DateTimeInterface::diff</methodname> during DST
   changeover</title>
   <programlisting role="php">
<![CDATA[
<?php
$originalTime = new DateTimeImmutable("2021-10-30 09:00:00 Europe/London");
$targetTime = new DateTimeImmutable("2021-10-31 08:30:00 Europe/London");
$interval = $originalTime->diff($targetTime);
echo $interval->format("%H:%I:%S (Full days: %a)"), "\n";
?>
]]>
   </programlisting>
   &example.outputs;
   <screen>
<![CDATA[
24:30:00 (Full days: 0)
]]>
   </screen>
  </example>

  <example>
   <title><methodname>DateTimeInterface::diff</methodname> range</title>
   <para>
    The value that the method returns is the exact amount of time to get from
    <parameter>$this</parameter> to <parameter>$targetObject</parameter>.
    Comparing January 1st to December 31st returns therefore 364, and not 365,
    days (for non-leap years).
   </para>
   <programlisting role="php">
<![CDATA[
<?php
$originalTime = new DateTimeImmutable("2023-01-01 UTC");
$targetTime = new DateTimeImmutable("2023-12-31 UTC");
$interval = $originalTime->diff($targetTime);
echo "Full days: ", $interval->format("%a"), "\n";
?>
]]>
   </programlisting>
   &example.outputs;
   <screen>
<![CDATA[
Full days: 364
]]>
   </screen>
  </example>

  <example>
   <title><classname>DateTime</classname> object comparison</title>
   <note>
    <para>
     <classname>DateTimeImmutable</classname> and
     <classname>DateTime</classname> objects can be compared using
     <link linkend="language.operators.comparison">comparison operators</link>.
    </para>
   </note>
   <programlisting role="php">
<![CDATA[
<?php
$date1 = new DateTime("now");
$date2 = new DateTime("tomorrow");

var_dump($date1 == $date2);
var_dump($date1 < $date2);
var_dump($date1 > $date2);
?>
]]>
  </programlisting>
  &example.outputs;
  <screen>
<![CDATA[
bool(false)
bool(true)
bool(false)
]]>
  </screen>
  </example>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <simplelist>
   <member><function>DateInterval::format</function></member>
   <member><function>DateTime::add</function></member>
   <member><function>DateTime::sub</function></member>
  </simplelist>
 </refsect1>

</refentry>
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