mb-detect-encoding.xml

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<!-- $Revision$ -->
<refentry xml:id="function.mb-detect-encoding" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
 <refnamediv>
  <refname>mb_detect_encoding</refname>
  <refpurpose>Detect character encoding</refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type class="union"><type>string</type><type>false</type></type><methodname>mb_detect_encoding</methodname>
   <methodparam><type>string</type><parameter>string</parameter></methodparam>
   <methodparam choice="opt"><type class="union"><type>array</type><type>string</type><type>null</type></type><parameter>encodings</parameter><initializer>&null;</initializer></methodparam>
   <methodparam choice="opt"><type>bool</type><parameter>strict</parameter><initializer>&false;</initializer></methodparam>
  </methodsynopsis>
  <para>
   Detects the most likely character encoding for <type>string</type> <parameter>string</parameter>
   from an ordered list of candidates.
  </para>
  <para>
   Automatic detection of the intended character encoding can never be entirely reliable;
   without some additional information, it is similar to decoding an encrypted string
   without the key. It is always preferable to use an indication of character encoding
   stored or transmitted with the data, such as a "Content-Type" HTTP header.
  </para>
  <para>
   This function is most useful with multibyte encodings, where not all sequences of
   bytes form a valid string. If the input string contains such a sequence, that
   encoding will be rejected, and the next encoding checked.
  </para>

  <warning>
   <title>The result is not accurate</title>
   <para>
    The name of this function is misleading, it performs "guessing" rather than "detection".
   </para>
   <para>
    The guesses are far from accurate, and therefore you cannot use this function to accurately
    detect the correct character encoding.
   </para>
  </warning>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>string</parameter></term>
     <listitem>
      <para>
       The <type>string</type> being inspected.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>encodings</parameter></term>
     <listitem>
      <para>
       A list of character encodings to try, in order. The list may be specified as
       an array of strings, or a single string separated by commas.
      </para>
      <para>
       If <parameter>encodings</parameter> is omitted or &null;,
       the current detect_order (set with the <link linkend="ini.mbstring.detect-order">
       mbstring.detect_order</link> configuration option, or <function>mb_detect_order</function>
       function) will be used.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>strict</parameter></term>
     <listitem>
      <para>
       Controls the behaviour when <parameter>string</parameter>
       is not valid in any of the listed <parameter>encodings</parameter>.
       If <parameter>strict</parameter> is set to &false;, the closest matching
       encoding will be returned; if <parameter>strict</parameter> is set to &true;,
       &false; will be returned.
      </para>
      <para>
       The default value for <parameter>strict</parameter> can be set
       with the <link linkend="ini.mbstring.strict-detection">
       mbstring.strict_detection</link> configuration option.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   The detected character encoding, or &false; if the string is not valid
   in any of the listed encodings.
  </para>
 </refsect1>

 <refsect1 role="changelog">
  &reftitle.changelog;
  <informaltable>
   <tgroup cols="2">
    <thead>
     <row>
      <entry>&Version;</entry>
      <entry>&Description;</entry>
     </row>
    </thead>
    <tbody>
     <row>
      <entry>8.2.0</entry>
      <entry>
       <function>mb_detect_encoding</function> will no longer return
       the following non text encodings:
       <literal>"Base64"</literal>, <literal>"QPrint"</literal>,
       <literal>"UUencode"</literal>, <literal>"HTML entities"</literal>,
       <literal>"7 bit"</literal> and <literal>"8 bit"</literal>.
      </entry>
     </row>
    </tbody>
   </tgroup>
  </informaltable>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title><function>mb_detect_encoding</function> example</title>
    <programlisting role="php">
<![CDATA[
<?php

$str = "\x95\xB6\x8E\x9A\x83\x52\x81\x5B\x83\x68";

// Detect character encoding with current detect_order
var_dump(mb_detect_encoding($str));

// "auto" is expanded according to mbstring.language
var_dump(mb_detect_encoding($str, "auto"));

// Specify "encodings" parameter by list separated by comma
var_dump(mb_detect_encoding($str, "JIS, eucjp-win, sjis-win"));

// Use array to specify "encodings" parameter
$encodings = [
  "ASCII",
  "JIS",
  "EUC-JP"
];
var_dump(mb_detect_encoding($str, $encodings));
?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
string(5) "ASCII"
string(5) "ASCII"
string(8) "SJIS-win"
string(5) "ASCII"
]]>
    </screen>
   </example>
  </para>
  <para>
   <example>
    <title>Effect of <parameter>strict</parameter> parameter</title>
    <programlisting role="php">
     <![CDATA[
<?php
// 'áéóú' encoded in ISO-8859-1
$str = "\xE1\xE9\xF3\xFA";

// The string is not valid ASCII or UTF-8, but UTF-8 is considered a closer match
var_dump(mb_detect_encoding($str, ['ASCII', 'UTF-8'], false));
var_dump(mb_detect_encoding($str, ['ASCII', 'UTF-8'], true));

// If a valid encoding is found, the strict parameter does not change the result
var_dump(mb_detect_encoding($str, ['ASCII', 'UTF-8', 'ISO-8859-1'], false));
var_dump(mb_detect_encoding($str, ['ASCII', 'UTF-8', 'ISO-8859-1'], true));
?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
string(5) "UTF-8"
bool(false)
string(10) "ISO-8859-1"
string(10) "ISO-8859-1"
]]>
    </screen>
   </example>
  </para>
  <para>
   In some cases, the same sequence of bytes may form a valid string in multiple
   character encodings, and it is impossible to know which interpretation was
   intended. For instance, among many others, the byte sequence "\xC4\xA2" could be:
  </para>
  <para>
   <simplelist>
    <member>
     "Ä¢" (U+00C4 LATIN CAPITAL LETTER A WITH DIAERESIS followed by U+00A2 CENT SIGN)
     encoded in any of ISO-8859-1, ISO-8859-15, or Windows-1252
    </member>
    <member>
     "ФЂ" (U+0424 CYRILLIC CAPITAL LETTER EF followed by U+0402 CYRILLIC CAPITAL LETTER
     DJE) encoded in ISO-8859-5
    </member>
    <member>
     "Ģ" (U+0122 LATIN CAPITAL LETTER G WITH CEDILLA) encoded in UTF-8
    </member>
   </simplelist>
  </para>
  <para>
   <example>
    <title>Effect of order when multiple encodings match</title>
    <programlisting role="php">
     <![CDATA[
<?php
$str = "\xC4\xA2";

// The string is valid in all three encodings, so the first one listed will be returned
var_dump(mb_detect_encoding($str, ['UTF-8', 'ISO-8859-1', 'ISO-8859-5']));
var_dump(mb_detect_encoding($str, ['ISO-8859-1', 'ISO-8859-5', 'UTF-8']));
var_dump(mb_detect_encoding($str, ['ISO-8859-5', 'UTF-8', 'ISO-8859-1']));
?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
string(5) "UTF-8"
string(10) "ISO-8859-1"
string(10) "ISO-8859-5"
]]>
    </screen>
   </example>
  </para>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><function>mb_detect_order</function></member>
   </simplelist>
  </para>
 </refsect1>

</refentry>
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