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<refentry xml:id="function.mb-ereg-replace-callback" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
 <refnamediv>
  <refname>mb_ereg_replace_callback</refname>
  <refpurpose>Perform a regular expression search and replace with multibyte support using a callback
  </refpurpose>
 </refnamediv>
   
 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type class="union"><type>string</type><type>false</type><type>null</type></type><methodname>mb_ereg_replace_callback</methodname>
   <methodparam><type>string</type><parameter>pattern</parameter></methodparam>
   <methodparam><type>callable</type><parameter>callback</parameter></methodparam>
   <methodparam><type>string</type><parameter>string</parameter></methodparam>
   <methodparam choice="opt"><type class="union"><type>string</type><type>null</type></type><parameter>options</parameter><initializer>&null;</initializer></methodparam>
  </methodsynopsis>
  <para>
   Scans <parameter>string</parameter> for matches to
   <parameter>pattern</parameter>, then replaces the matched text
   with the output of <parameter>callback</parameter> function.  
  </para>
  <para>
    The behavior of this function is almost identical to <function>mb_ereg_replace</function>, 
    except for the fact that instead of
    <parameter>replacement</parameter> parameter, one should specify a
    <parameter>callback</parameter>.
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>pattern</parameter></term>
     <listitem>
      <para>
       The regular expression pattern.
      </para>
      <para>
       Multibyte characters may be used in <parameter>pattern</parameter>.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>callback</parameter></term>
     <listitem>
      <para>
        A callback that will be called and passed an array of matched elements
        in the  <parameter>subject</parameter> string. The callback should
       return the replacement string.
      </para>
      <para>
        You'll often need the <parameter>callback</parameter> function
        for a <function>mb_ereg_replace_callback</function> in just one place.
        In this case you can use an
        <link linkend="functions.anonymous">anonymous function</link> to
        declare the callback within the call to
        <function>mb_ereg_replace_callback</function>. By doing it this way
        you have all information for the call in one place and do not
        clutter the function namespace with a callback function's name
        not used anywhere else.        
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>string</parameter></term>
     <listitem>
      <para>
       The <type>string</type> being checked.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>options</parameter></term>
     <listitem>
      <para>
       The search option. See <function>mb_regex_set_options</function> for explanation.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>
 
 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   The resultant <type>string</type> on success, or &false; on error.
   If <parameter>string</parameter> is not valid for the current encoding, &null;
   is returned.
  </para>
 </refsect1>

 <refsect1 role="changelog">
  &reftitle.changelog;
  <para>
   <informaltable>
    <tgroup cols="2">
     <thead>
      <row>
       <entry>&Version;</entry>
       <entry>&Description;</entry>
      </row>
     </thead>
     <tbody>
      <row>
       <entry>8.0.0</entry>
       <entry>
        <parameter>options</parameter> is nullable now.
       </entry>
      </row>
      <row>
       <entry>7.1.0</entry>
       <entry>
        The function checks whether <parameter>string</parameter> is valid for the
        current encoding.
       </entry>
      </row>
     </tbody>
    </tgroup>
   </informaltable>
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title><function>mb_ereg_replace_callback</function> example</title>
    <programlisting role="php">
<![CDATA[
<?php
// this text was used in 2002
// we want to get this up to date for 2003
$text = "April fools day is 04/01/2002\n";
$text.= "Last christmas was 12/24/2001\n";
// the callback function
function next_year($matches)
{
  // as usual: $matches[0] is the complete match
  // $matches[1] the match for the first subpattern
  // enclosed in '(...)' and so on
  return $matches[1].($matches[2]+1);
}
echo mb_ereg_replace_callback(
            "(\d{2}/\d{2}/)(\d{4})",
            "next_year",
            $text);

?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
April fools day is 04/01/2003
Last christmas was 12/24/2002
]]>
    </screen>
   </example>
  </para>
  <para>
   <example>
    <title><function>mb_ereg_replace_callback</function> using anonymous function</title>
    <programlisting role="php">
<![CDATA[
<?php
// this text was used in 2002
// we want to get this up to date for 2003
$text = "April fools day is 04/01/2002\n";
$text.= "Last christmas was 12/24/2001\n";

echo mb_ereg_replace_callback(
            "(\d{2}/\d{2}/)(\d{4})",
            function ($matches) {
               return $matches[1].($matches[2]+1);
            },
            $text);
?>
]]>
    </programlisting>
   </example>
  </para>
 </refsect1>

 <refsect1 role="notes">
  &reftitle.notes;

  &note.mbstring.encoding.internal;
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><function>mb_regex_encoding</function></member>
    <member><function>mb_ereg_replace</function></member>
    <member><link linkend="functions.anonymous">Anonymous functions</link></member>
   </simplelist>
  </para>
 </refsect1>

</refentry>
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