language/control-structures/foreach.xml
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<!-- $Revision$ -->
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<sect1 xml:id="control-structures.foreach" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
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<title><literal>foreach</literal></title>
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<title>foreach</title>
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<?phpdoc print-version-for="foreach"?>
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<para>
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The <literal>foreach</literal> construct provides an easy way to
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<informalexample>
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<programlisting>
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<![CDATA[
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foreach (array_expression as $value)
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foreach (iterable_expression as $value)
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statement
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foreach (array_expression as $key => $value)
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foreach (iterable_expression as $key => $value)
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statement
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]]>
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</programlisting>
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</informalexample>
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</para>
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<simpara>
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The first form loops over the array given by
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<literal>array_expression</literal>. On each iteration, the value of
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the current element is assigned to <literal>$value</literal> and
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the internal array pointer is advanced by one (so on the next
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iteration, you'll be looking at the next element).
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The first form traverses the iterable given by
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<literal>iterable_expression</literal>. On each iteration, the value of
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the current element is assigned to <literal>$value</literal>.
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</simpara>
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<simpara>
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The second form will additionally assign the current element's key to
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the <literal>$key</literal> variable on each iteration.
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</simpara>
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<simpara>
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Note that <literal>foreach</literal> does not modify the internal array
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pointer, which is used by functions such as <function>current</function>
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and <function>key</function>.
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</simpara>
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<simpara>
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It is possible to
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<link linkend="language.oop5.iterations">customize object iteration</link>.
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</simpara>
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<para>
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<note>
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<para>
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In PHP 5, when <literal>foreach</literal> first starts executing, the
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internal array pointer is automatically reset to the first element of the
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array. This means that you do not need to call <function>reset</function>
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before a <literal>foreach</literal> loop.
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</para>
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<para>
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As <literal>foreach</literal> relies on the internal array pointer in PHP
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5, changing it within the loop may lead to unexpected behavior.
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</para>
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<para>
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In PHP 7, <literal>foreach</literal> does not use the internal array
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pointer.
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</para>
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</note>
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</para>
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<para>
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In order to be able to directly modify array elements within the loop precede
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<literal>$value</literal> with &amp;. In that case the value will be assigned by
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</programlisting>
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</informalexample>
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</para>
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<para>
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Referencing <literal>$value</literal> is only possible if the iterated array can be
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referenced (i.e. if it is a variable). The following code won't work:
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<informalexample>
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<programlisting role="php">
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<![CDATA[
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<?php
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foreach (array(1, 2, 3, 4) as &$value) {
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$value = $value * 2;
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}
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?>
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]]>
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</programlisting>
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</informalexample>
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</para>
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<warning>
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<para>
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Reference of a <literal>$value</literal> and the last array element
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remain even after the <literal>foreach</literal> loop. It is recommended
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to destroy it by <function>unset</function>.
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Otherwise you will experience the following behavior:
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</para>
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</warning>
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<para>
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<note>
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<para>
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<literal>foreach</literal> does not support the ability to
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suppress error messages using '@'.
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</para>
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</note>
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</para>
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<para>
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You may have noticed that the following are functionally
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identical:
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<informalexample>
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<programlisting role="php">
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<![CDATA[
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<?php
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$arr = array("one", "two", "three");
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reset($arr);
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while (list(, $value) = each($arr)) {
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echo "Value: $value<br />\n";
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$arr = array(1, 2, 3, 4);
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foreach ($arr as &$value) {
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$value = $value * 2;
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}
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// $arr is now array(2, 4, 6, 8)
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// without an unset($value), $value is still a reference to the last item: $arr[3]
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foreach ($arr as $value) {
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echo "Value: $value<br />\n";
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foreach ($arr as $key => $value) {
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// $arr[3] will be updated with each value from $arr...
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echo "{$key} => {$value} ";
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print_r($arr);
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}
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// ...until ultimately the second-to-last value is copied onto the last value
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// output:
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// 0 => 2 Array ( [0] => 2, [1] => 4, [2] => 6, [3] => 2 )
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// 1 => 4 Array ( [0] => 2, [1] => 4, [2] => 6, [3] => 4 )
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// 2 => 6 Array ( [0] => 2, [1] => 4, [2] => 6, [3] => 6 )
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// 3 => 6 Array ( [0] => 2, [1] => 4, [2] => 6, [3] => 6 )
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?>
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]]>
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</programlisting>
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</informalexample>
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</para>
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</warning>
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<para>
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The following are also functionally identical:
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It is possible to iterate a constant array's value by reference:
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<informalexample>
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<programlisting role="php">
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<![CDATA[
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<?php
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$arr = array("one", "two", "three");
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reset($arr);
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while (list($key, $value) = each($arr)) {
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echo "Key: $key; Value: $value<br />\n";
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}
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foreach ($arr as $key => $value) {
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echo "Key: $key; Value: $value<br />\n";
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foreach (array(1, 2, 3, 4) as &$value) {
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$value = $value * 2;
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}
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?>
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]]>
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</informalexample>
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</para>
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<para>
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<note>
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<para>
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<literal>foreach</literal> does not support the ability to
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suppress error messages using
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<literal linkend="language.operators.errorcontrol">@</literal>.
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</para>
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</note>
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</para>
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<para>
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Some more examples to demonstrate usage:
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<informalexample>
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<programlisting role="php">
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<?phpdoc print-version-for="foreach.list"?>
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<para>
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PHP 5.5 added the ability to iterate over an array of arrays and unpack the
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It is possible to iterate over an array of arrays and unpack the
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nested array into loop variables by providing a <function>list</function>
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as the value.
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</para>
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</informalexample>
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</para>
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</sect2>
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</sect1>
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<!-- Keep this comment at the end of the file
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