mirror of
https://github.com/sigmasternchen/php-doc-en
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278 lines
7.7 KiB
XML
278 lines
7.7 KiB
XML
<?xml version="1.0" encoding="utf-8"?>
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<!-- $Revision$ -->
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<refentry xml:id="function.substr" xmlns="http://docbook.org/ns/docbook">
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<refnamediv>
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<refname>substr</refname>
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<refpurpose>Return part of a string</refpurpose>
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</refnamediv>
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<refsect1 role="description">
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&reftitle.description;
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<methodsynopsis>
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<type>string</type><methodname>substr</methodname>
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<methodparam><type>string</type><parameter>string</parameter></methodparam>
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<methodparam><type>int</type><parameter>offset</parameter></methodparam>
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<methodparam choice="opt"><type class="union"><type>int</type><type>null</type></type><parameter>length</parameter><initializer>&null;</initializer></methodparam>
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</methodsynopsis>
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<para>
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Returns the portion of <parameter>string</parameter> specified by the
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<parameter>offset</parameter> and <parameter>length</parameter> parameters.
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</para>
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</refsect1>
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<refsect1 role="parameters">
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&reftitle.parameters;
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<para>
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<variablelist>
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<varlistentry>
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<term><parameter>string</parameter></term>
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<listitem>
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<para>
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The input string.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>offset</parameter></term>
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<listitem>
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<para>
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If <parameter>offset</parameter> is non-negative, the returned string
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will start at the <parameter>offset</parameter>'th position in
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<parameter>string</parameter>, counting from zero. For instance,
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in the string '<literal>abcdef</literal>', the character at
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position <literal>0</literal> is '<literal>a</literal>', the
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character at position <literal>2</literal> is
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'<literal>c</literal>', and so forth.
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</para>
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<para>
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If <parameter>offset</parameter> is negative, the returned string
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will start at the <parameter>offset</parameter>'th character
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from the end of <parameter>string</parameter>.
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</para>
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<para>
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If <parameter>string</parameter> is less than
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<parameter>offset</parameter> characters long, an empty string will be returned.
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</para>
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<para>
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<example>
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<title>Using a negative <parameter>offset</parameter></title>
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<programlisting role="php">
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<![CDATA[
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<?php
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$rest = substr("abcdef", -1); // returns "f"
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$rest = substr("abcdef", -2); // returns "ef"
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$rest = substr("abcdef", -3, 1); // returns "d"
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?>
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]]>
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</programlisting>
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</example>
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>length</parameter></term>
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<listitem>
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<para>
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If <parameter>length</parameter> is given and is positive, the string
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returned will contain at most <parameter>length</parameter> characters
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beginning from <parameter>offset</parameter> (depending on the length of
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<parameter>string</parameter>).
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</para>
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<para>
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If <parameter>length</parameter> is given and is negative, then that many
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characters will be omitted from the end of <parameter>string</parameter>
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(after the start position has been calculated when a
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<parameter>offset</parameter> is negative). If
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<parameter>offset</parameter> denotes the position of this truncation or
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beyond, an empty string will be returned.
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</para>
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<para>
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If <parameter>length</parameter> is given and is <literal>0</literal>,
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&false; or &null;, an empty string will be returned.
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</para>
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<para>
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If <parameter>length</parameter> is omitted, the substring starting from
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<parameter>offset</parameter> until the end of the string will be
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returned.
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</para>
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<example>
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<title>Using a negative <parameter>length</parameter></title>
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<programlisting role="php">
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<![CDATA[
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<?php
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$rest = substr("abcdef", 0, -1); // returns "abcde"
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$rest = substr("abcdef", 2, -1); // returns "cde"
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$rest = substr("abcdef", 4, -4); // returns ""; prior to PHP 8.0.0, false was returned
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$rest = substr("abcdef", -3, -1); // returns "de"
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?>
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]]>
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</programlisting>
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</example>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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</refsect1>
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<refsect1 role="returnvalues">
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&reftitle.returnvalues;
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<para>
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Returns the extracted part of <parameter>string</parameter>, or
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an empty string.
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</para>
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</refsect1>
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<refsect1 role="changelog">
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&reftitle.changelog;
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<informaltable>
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<tgroup cols="2">
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<thead>
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<row>
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<entry>&Version;</entry>
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<entry>&Description;</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>8.0.0</entry>
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<entry>
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<parameter>length</parameter> is nullable now.
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</entry>
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</row>
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<row>
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<entry>8.0.0</entry>
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<entry>
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The function returns an empty string where it previously returned &false;.
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</entry>
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</row>
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</tbody>
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</tgroup>
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</informaltable>
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</refsect1>
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<refsect1 role="examples">
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&reftitle.examples;
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<para>
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<example>
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<title>Basic <function>substr</function> usage</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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echo substr('abcdef', 1); // bcdef
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echo substr('abcdef', 1, 3); // bcd
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echo substr('abcdef', 0, 4); // abcd
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echo substr('abcdef', 0, 8); // abcdef
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echo substr('abcdef', -1, 1); // f
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// Accessing single characters in a string
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// can also be achieved using "square brackets"
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$string = 'abcdef';
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echo $string[0]; // a
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echo $string[3]; // d
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echo $string[strlen($string)-1]; // f
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?>
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]]>
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</programlisting>
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</example>
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<example>
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<title><function>substr</function> casting behaviour</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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class apple {
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public function __toString() {
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return "green";
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}
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}
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echo "1) ".var_export(substr("pear", 0, 2), true).PHP_EOL;
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echo "2) ".var_export(substr(54321, 0, 2), true).PHP_EOL;
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echo "3) ".var_export(substr(new apple(), 0, 2), true).PHP_EOL;
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echo "4) ".var_export(substr(true, 0, 1), true).PHP_EOL;
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echo "5) ".var_export(substr(false, 0, 1), true).PHP_EOL;
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echo "6) ".var_export(substr("", 0, 1), true).PHP_EOL;
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echo "7) ".var_export(substr(1.2e3, 0, 4), true).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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1) 'pe'
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2) '54'
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3) 'gr'
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4) '1'
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5) ''
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6) ''
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7) '1200'
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]]>
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</screen>
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</example>
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<example>
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<title>Invalid Character Range</title>
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<para>
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If an invalid character range is requested, <function>substr</function> returns
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an empty string as of PHP 8.0.0; previously, &false; was returned instead.
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</para>
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<example>
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<programlisting role="php">
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<![CDATA[
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<?php
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var_dump(substr('a', 2));
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?>
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]]>
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</programlisting>
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&example.outputs.8;
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<screen>
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<![CDATA[
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string(0) ""
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]]>]
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</screen>
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&example.outputs.7;
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<screen>
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<![CDATA[
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bool(false)
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]]>
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</screen>
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</example>
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</example>
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</para>
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</refsect1>
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<refsect1 role="seealso">
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&reftitle.seealso;
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<para>
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<simplelist>
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<member><function>strrchr</function></member>
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<member><function>substr_replace</function></member>
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<member><function>preg_match</function></member>
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<member><function>trim</function></member>
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<member><function>mb_substr</function></member>
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<member><function>wordwrap</function></member>
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<member><link linkend="language.types.string.substr">String access and modification by character</link></member>
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</simplelist>
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</para>
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</refsect1>
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</refentry>
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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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