mb_detect_encoding

(PHP 4 >= 4.0.6, PHP 5, PHP 7, PHP 8)

mb_detect_encoding文字エンコーディングを検出する

説明

mb_detect_encoding(string $string, array|string|null $encodings = null, bool $strict = false): string|false

エンコーディングの候補の一覧から、 文字列 string のもっとも可能性が高い文字エンコーディングを検出します。

追加の情報なしに、 意図した文字エンコーディングを自動で検出する行為は、 全く役に立ちません。 これは、暗号化された文字列を鍵なしにデコードする行為に似ています。 "Content-Type" HTTP ヘッダのような、 データを転送された際に付いてくる情報や、 保存された文字エンコーディングに関する指示を指定することが常に望ましいです。

この関数は、全ての文字列が正しいバイト配列とは限らない マルチバイト文字列を指定するともっとも役に立ちます。 入力となる文字列に誤ったバイトが含まれていた場合、 そのエンコーディングは採用されず、次のものを試します。

パラメータ

string

調べる対象の文字列。

encodings

文字エンコーディングの一覧を試す順番に指定します。 このリストは、文字列の配列または、 カンマ区切りのリストで指定できます。

encodings が省略された場合、 または null の場合、 現在の detect_order ( mbstring.detect_order 設定オプション または mb_detect_order() で設定したもの) を使います。

strict

encodings で指定された 文字エンコーディングのリストの全てに対して、 不正と判定された場合の振る舞いを指定します。 strictfalse の場合、 もっとも近いと判定された文字エンコーディングが返されます。 stricttrue にした場合、 false が返されます。

strict のデフォルト値は mbstring.strict_detection 設定オプションで指定できます。

戻り値

検出した文字エンコーディングを返します。 指定したエンコーディングの全てに対して、不正と判定された場合は false を返します。

変更履歴

バージョン 説明
8.2.0 mb_detect_encoding() は、 以下のテキストでないエンコーディングを返さなくなりました: "Base64", "QPrint", "UUencode", "HTML entities", "7 bit", "8 bit"

例1 mb_detect_encoding() の例

<?php
// 現在のdetect_orderで文字エンコーディングを検出
echo mb_detect_encoding($str);

// "auto" は mbstring.language の設定を使って展開されます
echo mb_detect_encoding($str, "auto");

// 文字エンコーディングをカンマ区切りのリストで指定することで、encodings 引数を指定
echo mb_detect_encoding($str, "JIS, eucjp-win, sjis-win");

// encodings 引数を配列で指定
$encodings = [
"ASCII",
"JIS",
"EUC-JP"
];
echo
mb_detect_encoding($str, $encodings);
?>

例2 strict パラメーターの効果

<?php
// 'áéóú' は ISO-8859-1 でエンコードされています
$str = "\xE1\xE9\xF3\xFA";

// この文字列は、ASCII または UTF-8 的には正しくありませんが、
// UTF-8 がもっとも近いと判定されます
var_dump(mb_detect_encoding($str, ['ASCII', 'UTF-8'], false));
var_dump(mb_detect_encoding($str, ['ASCII', 'UTF-8'], true));

// 正しいエンコーディングが見つかった場合、
// strict パラメータを指定しても結果は変わりません
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));
?>

上の例の出力は以下となります。

string(5) "UTF-8"
bool(false)
string(10) "ISO-8859-1"
string(10) "ISO-8859-1"

場合によっては、同じバイト配列が、 複数の文字エンコーディング的に正しいかもしれませんが、 どの解釈が意図されたものなのかを知ることは不可能です。 たとえば、 バイト配列 "\xC4\xA2" は、 以下のように解釈できます:

  • "Ä¢" (U+00C4 LATIN CAPITAL LETTER A WITH DIAERESIS のあとに、U+00A2 CENT SIGN が続いたもの) これらは、ISO-8859-1, ISO-8859-15, Windows-1252 でエンコードされたものと解釈できます。
  • "ФЂ" (U+0424 CYRILLIC CAPITAL LETTER EF のあとに、 U+0402 CYRILLIC CAPITAL LETTER DJE が続いたもの) これは、ISO-8859-5 でエンコードされたものと解釈できます。
  • "Ģ" (U+0122 LATIN CAPITAL LETTER G WITH CEDILLA) これは、UTF-8 でエンコードされたものと解釈できます。

例3 複数のエンコーディングと一致した場合の効果

<?php
$str
= "\xC4\xA2";

// 3つ全てのエンコーディングに照らして正しい文字列なので、
// 最初のひとつが返されます。
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']));
?>

上の例の出力は以下となります。

string(5) "UTF-8"
string(10) "ISO-8859-1"
string(10) "ISO-8859-5"

参考

  • mb_detect_order() - 文字エンコーディング検出順序を設定あるいは取得する

add a note

User Contributed Notes 26 notes

up
84
Gerg Tisza
13 years ago
If you try to use mb_detect_encoding to detect whether a string is valid UTF-8, use the strict mode, it is pretty worthless otherwise.

<?php
$str
= 'áéóú'; // ISO-8859-1
mb_detect_encoding($str, 'UTF-8'); // 'UTF-8'
mb_detect_encoding($str, 'UTF-8', true); // false
?>
up
17
mta59066 at gmail dot com
1 year ago
The documentation is no longer correct for php8.1 and mb_detect_encoding no longer supports order of encodings. The example outputs given in the documentation are also no longer correct for php8.1. This is somewhat explained here https://github.com/php/php-src/issues/8279

I understand the previous ambiguity in these functions, but in my option 8.1 should have deprecated mb_detect_encoding and mb_detect_order and came up with different functions. It now tries to find the encoding that will use the least amount of space regardless of the order, and I am not sure who needs that.

Below is an example function that will do what mb_detect_encoding was doing prior to the 8.1 change.

<?php

function mb_detect_enconding_in_order(string $string, array $encodings): string|false
{
foreach(
$encodings as $enc) {
if (
mb_check_encoding($string, $enc)) {
return
$enc;
}
}
return
false;
}

?>
up
5
geompse at gmail dot com
1 year ago
Major undocumented breaking change since 8.1.7
https://3v4l.org/BLjZ3

Make sure to replace mb_detect_encoding with a loop of calls to mb_check_encoding
up
22
Chrigu
18 years ago
If you need to distinguish between UTF-8 and ISO-8859-1 encoding, list UTF-8 first in your encoding_list:
mb_detect_encoding($string, 'UTF-8, ISO-8859-1');

if you list ISO-8859-1 first, mb_detect_encoding() will always return ISO-8859-1.
up
18
chris AT w3style.co DOT uk
17 years ago
Based upon that snippet below using preg_match() I needed something faster and less specific. That function works and is brilliant but it scans the entire strings and checks that it conforms to UTF-8. I wanted something purely to check if a string contains UTF-8 characters so that I could switch character encoding from iso-8859-1 to utf-8.

I modified the pattern to only look for non-ascii multibyte sequences in the UTF-8 range and also to stop once it finds at least one multibytes string. This is quite a lot faster.

<?php

function detectUTF8($string)
{
return
preg_match('%(?:
[\xC2-\xDF][\x80-\xBF] # non-overlong 2-byte
|\xE0[\xA0-\xBF][\x80-\xBF] # excluding overlongs
|[\xE1-\xEC\xEE\xEF][\x80-\xBF]{2} # straight 3-byte
|\xED[\x80-\x9F][\x80-\xBF] # excluding surrogates
|\xF0[\x90-\xBF][\x80-\xBF]{2} # planes 1-3
|[\xF1-\xF3][\x80-\xBF]{3} # planes 4-15
|\xF4[\x80-\x8F][\x80-\xBF]{2} # plane 16
)+%xs'
, $string);
}

?>
up
12
dennis at nikolaenko dot ru
15 years ago
Beware of bug to detect Russian encodings
http://bugs.php.net/bug.php?id=38138
up
17
nat3738 at gmail dot com
14 years ago
A simple way to detect UTF-8/16/32 of file by its BOM (not work with string or file without BOM)

<?php
// Unicode BOM is U+FEFF, but after encoded, it will look like this.
define ('UTF32_BIG_ENDIAN_BOM' , chr(0x00) . chr(0x00) . chr(0xFE) . chr(0xFF));
define ('UTF32_LITTLE_ENDIAN_BOM', chr(0xFF) . chr(0xFE) . chr(0x00) . chr(0x00));
define ('UTF16_BIG_ENDIAN_BOM' , chr(0xFE) . chr(0xFF));
define ('UTF16_LITTLE_ENDIAN_BOM', chr(0xFF) . chr(0xFE));
define ('UTF8_BOM' , chr(0xEF) . chr(0xBB) . chr(0xBF));

function
detect_utf_encoding($filename) {

$text = file_get_contents($filename);
$first2 = substr($text, 0, 2);
$first3 = substr($text, 0, 3);
$first4 = substr($text, 0, 3);

if (
$first3 == UTF8_BOM) return 'UTF-8';
elseif (
$first4 == UTF32_BIG_ENDIAN_BOM) return 'UTF-32BE';
elseif (
$first4 == UTF32_LITTLE_ENDIAN_BOM) return 'UTF-32LE';
elseif (
$first2 == UTF16_BIG_ENDIAN_BOM) return 'UTF-16BE';
elseif (
$first2 == UTF16_LITTLE_ENDIAN_BOM) return 'UTF-16LE';
}
?>
up
5
rl at itfigures dot nl
16 years ago
I used Chris's function "detectUTF8" to detect the need from conversion from utf8 to 8859-1, which works fine. I did have a problem with the following iconv-conversion.

The problem is that the iconv-conversion to 8859-1 (with //TRANSLIT) replaces the euro-sign with EUR, although it is common practice that \x80 is used as the euro-sign in the 8859-1 charset.

I could not use 8859-15 since that mangled some other characters, so I added 2 str_replace's:

if(detectUTF8($str)){
$str=str_replace("\xE2\x82\xAC","&euro;",$str);
$str=iconv("UTF-8","ISO-8859-1//TRANSLIT",$str);
$str=str_replace("&euro;","\x80",$str);
}

If html-output is needed the last line is not necessary (and even unwanted).
up
6
eyecatchup at gmail dot com
10 years ago
Just a note: Instead of using the often recommended (rather complex) regular expression by W3C (http://www.w3.org/International/questions/qa-forms-utf-8.en.php), you can simply use the 'u' modifier to test a string for UTF-8 validity:

<?php
if (preg_match("//u", $string)) {
// $string is valid UTF-8
}
up
6
hmdker at gmail dot com
15 years ago
Function to detect UTF-8, when mb_detect_encoding is not available it may be useful.

<?php
function is_utf8($str) {
$c=0; $b=0;
$bits=0;
$len=strlen($str);
for(
$i=0; $i<$len; $i++){
$c=ord($str[$i]);
if(
$c > 128){
if((
$c >= 254)) return false;
elseif(
$c >= 252) $bits=6;
elseif(
$c >= 248) $bits=5;
elseif(
$c >= 240) $bits=4;
elseif(
$c >= 224) $bits=3;
elseif(
$c >= 192) $bits=2;
else return
false;
if((
$i+$bits) > $len) return false;
while(
$bits > 1){
$i++;
$b=ord($str[$i]);
if(
$b < 128 || $b > 191) return false;
$bits--;
}
}
}
return
true;
}
?>
up
2
garbage at iglou dot eu
6 years ago
For detect UTF-8, you can use:

if (preg_match('!!u', $str)) { echo 'utf-8'; }

- Norihiori
up
3
php-note-2005 at ryandesign dot com
19 years ago
Much simpler UTF-8-ness checker using a regular expression created by the W3C:

<?php

// Returns true if $string is valid UTF-8 and false otherwise.
function is_utf8($string) {

// From http://w3.org/International/questions/qa-forms-utf-8.html
return preg_match('%^(?:
[\x09\x0A\x0D\x20-\x7E] # ASCII
| [\xC2-\xDF][\x80-\xBF] # non-overlong 2-byte
| \xE0[\xA0-\xBF][\x80-\xBF] # excluding overlongs
| [\xE1-\xEC\xEE\xEF][\x80-\xBF]{2} # straight 3-byte
| \xED[\x80-\x9F][\x80-\xBF] # excluding surrogates
| \xF0[\x90-\xBF][\x80-\xBF]{2} # planes 1-3
| [\xF1-\xF3][\x80-\xBF]{3} # planes 4-15
| \xF4[\x80-\x8F][\x80-\xBF]{2} # plane 16
)*$%xs'
, $string);

}
// function is_utf8

?>
up
1
bmrkbyet at web dot de
10 years ago
a) if the FUNCTION mb_detect_encoding is not available:

### mb_detect_encoding ... iconv ###

<?php
// -------------------------------------------

if(!function_exists('mb_detect_encoding')) {
function
mb_detect_encoding($string, $enc=null) {

static
$list = array('utf-8', 'iso-8859-1', 'windows-1251');

foreach (
$list as $item) {
$sample = iconv($item, $item, $string);
if (
md5($sample) == md5($string)) {
if (
$enc == $item) { return true; } else { return $item; }
}
}
return
null;
}
}

// -------------------------------------------
?>

b) if the FUNCTION mb_convert_encoding is not available:

### mb_convert_encoding ... iconv ###

<?php
// -------------------------------------------

if(!function_exists('mb_convert_encoding')) {
function
mb_convert_encoding($string, $target_encoding, $source_encoding) {
$string = iconv($source_encoding, $target_encoding, $string);
return
$string;
}
}

// -------------------------------------------
?>
up
1
emoebel at web dot de
10 years ago
if the function " mb_detect_encoding" does not exist ...

... try:

<?php
// ----------------------------------------------------
if ( !function_exists('mb_detect_encoding') ) {

// ----------------------------------------------------------------
function mb_detect_encoding ($string, $enc=null, $ret=null) {

static
$enclist = array(
'UTF-8', 'ASCII',
'ISO-8859-1', 'ISO-8859-2', 'ISO-8859-3', 'ISO-8859-4', 'ISO-8859-5',
'ISO-8859-6', 'ISO-8859-7', 'ISO-8859-8', 'ISO-8859-9', 'ISO-8859-10',
'ISO-8859-13', 'ISO-8859-14', 'ISO-8859-15', 'ISO-8859-16',
'Windows-1251', 'Windows-1252', 'Windows-1254',
);

$result = false;

foreach (
$enclist as $item) {
$sample = iconv($item, $item, $string);
if (
md5($sample) == md5($string)) {
if (
$ret === NULL) { $result = $item; } else { $result = true; }
break;
}
}

return
$result;
}
// ----------------------------------------------------------------

}
// ----------------------------------------------------
?>

example / usage of: mb_detect_encoding()

<?php
// ------------------------------------------------------
function str_to_utf8 ($str) {

if (
mb_detect_encoding($str, 'UTF-8', true) === false) {
$str = utf8_encode($str);
}

return
$str;
}
// ------------------------------------------------------
?>

$txtstr = str_to_utf8($txtstr);
up
0
d_maksimov
1 year ago
It was helpful for my exec(...) call. When it returned cp866 or cp1251:

try {
$line = iconv('CP866', 'CP1251', $line);
} catch(Exception $e) {
}
return iconv('CP1251', 'UTF-8', $line);
up
0
recentUser at example dot com
5 years ago
In my environment (PHP 7.1.12),
"mb_detect_encoding()" doesn't work
where "mb_detect_order()" is not set appropriately.

To enable "mb_detect_encoding()" to work in such a case,
simply put "mb_detect_order('...')"
before "mb_detect_encoding()" in your script file.

Both
"ini_set('mbstring.language', '...');"
and
"ini_set('mbstring.detect_order', '...');"
DON'T work in script files for this purpose
whereas setting them in PHP.INI file may work.
up
0
lotushzy at gmail dot com
6 years ago
About function mb_detect_encoding, the link http://php.net/manual/zh/function.mb-detect-encoding.php , like this:
mb_detect_encoding('áéóú', 'UTF-8', true); // false
but now the result is not false, can you give me reason, thanks!
up
0
maarten
19 years ago
Sometimes mb_detect_string is not what you need. When using pdflib for example you want to VERIFY the correctness of utf-8. mb_detect_encoding reports some iso-8859-1 encoded text as utf-8.
To verify utf 8 use the following:

//
// utf8 encoding validation developed based on Wikipedia entry at:
// http://en.wikipedia.org/wiki/UTF-8
//
// Implemented as a recursive descent parser based on a simple state machine
// copyright 2005 Maarten Meijer
//
// This cries out for a C-implementation to be included in PHP core
//
function valid_1byte($char) {
if(!is_int($char)) return false;
return ($char & 0x80) == 0x00;
}

function valid_2byte($char) {
if(!is_int($char)) return false;
return ($char & 0xE0) == 0xC0;
}

function valid_3byte($char) {
if(!is_int($char)) return false;
return ($char & 0xF0) == 0xE0;
}

function valid_4byte($char) {
if(!is_int($char)) return false;
return ($char & 0xF8) == 0xF0;
}

function valid_nextbyte($char) {
if(!is_int($char)) return false;
return ($char & 0xC0) == 0x80;
}

function valid_utf8($string) {
$len = strlen($string);
$i = 0;
while( $i < $len ) {
$char = ord(substr($string, $i++, 1));
if(valid_1byte($char)) { // continue
continue;
} else if(valid_2byte($char)) { // check 1 byte
if(!valid_nextbyte(ord(substr($string, $i++, 1))))
return false;
} else if(valid_3byte($char)) { // check 2 bytes
if(!valid_nextbyte(ord(substr($string, $i++, 1))))
return false;
if(!valid_nextbyte(ord(substr($string, $i++, 1))))
return false;
} else if(valid_4byte($char)) { // check 3 bytes
if(!valid_nextbyte(ord(substr($string, $i++, 1))))
return false;
if(!valid_nextbyte(ord(substr($string, $i++, 1))))
return false;
if(!valid_nextbyte(ord(substr($string, $i++, 1))))
return false;
} // goto next char
}
return true; // done
}

for a drawing of the statemachine see: http://www.xs4all.nl/~mjmeijer/unicode.png and http://www.xs4all.nl/~mjmeijer/unicode2.png
up
-1
telemach
18 years ago
beware : even if you need to distinguish between UTF-8 and ISO-8859-1, and you the following detection order (as chrigu suggests)

mb_detect_encoding('accentu?e' , 'UTF-8, ISO-8859-1')

returns ISO-8859-1, while

mb_detect_encoding('accentu?' , 'UTF-8, ISO-8859-1')

returns UTF-8

bottom line : an ending '?' (and probably other accentuated chars) mislead mb_detect_encoding
up
-4
Anonymous
10 years ago
// -----------------------------------------------------------

if(!function_exists('mb_detect_encoding')) {

function mb_detect_encoding($string, $enc=null, $ret=true) {
$out=$enc;
static $list = array('utf-8', 'iso-8859-1', 'iso-8859-15', 'windows-1251');
foreach ($list as $item) {
$sample = iconv($item, $item, $string);
if (md5($sample) == md5($string)) { $out = ($ret !== false) ? true : $item; }
}
return $out;
}

}

// -----------------------------------------------------------
up
-5
yaqy at qq dot com
15 years ago
<?php
/*
*QQ: 290359552
* conver to Utf8 if $str is not equals to 'UTF-8'
*/
function convToUtf8($str)
{
if(
mb_detect_encoding($str,"UTF-8, ISO-8859-1, GBK")!="UTF-8" )
{

return
iconv("gbk","utf-8",$str);

}
else
{
return
$str;
}

}
?>
up
-5
lexonight at yahoo dot com
7 years ago
<?php
$file
= file_get_contents("somefile.txt");
$encodings = implode(',', mb_list_encodings());
echo
mb_detect_encoding($file, $encodings, true);
?>
seems to work
up
-7
matthijs at ischen dot nl
14 years ago
I seriously underestimated the importance of setlocale...
<?php
$strings
= array(
"mais coisas a pensar sobre diário ou dois!",
"plus de choses à penser à journalier ou à deux !",
"¡más cosas a pensar en diario o dos!",
"più cose da pensare circa giornaliere o due!",
"flere ting å tenke på hver dag eller to!",
"Další věcí, přemýšlet o každý den nebo dva!",
"mehr über Spaß spät schönen",
"më vonë gjatë fun bukur",
"több mint szórakozás késő csodálatos kenyér"
);

$convert = array();
setlocale(LC_CTYPE, 'de_DE.UTF-8');
foreach(
$strings as $string )
$convert[] = iconv('UTF-8', 'ASCII//TRANSLIT//IGNORE', $string);
?>

Produces the following:

Array
(
[0] => mais coisas a pensar sobre diario ou dois!
[1] => plus de choses a penser a journalier ou a deux !
[2] => ?mas cosas a pensar en diario o dos!
[3] => piu cose da pensare circa giornaliere o due!
[4] => flere ting aa tenke paa hver dag eller to!
[5] => Dalsi veci, premyslet o kazdy den nebo dva!
[6] => mehr ueber Spass spaet schoenen
[7] => me vone gjate fun bukur
[8] => toebb mint szorakozas keso csodalatos kenyer
)

whereas

<?php
$convert
= array();
setlocale(LC_CTYPE, 'nl_NL.UTF-8');
foreach(
$strings as $string )
$convert[] = iconv('UTF-8', 'ASCII//TRANSLIT//IGNORE', $string);
?>

produces:
Array
(
[0] => mais coisas a pensar sobre di?rio ou dois!
[1] => plus de choses ? penser ? journalier ou ? deux !
[2] => ?m?s cosas a pensar en diario o dos!
[3] => pi? cose da pensare circa giornaliere o due!
[4] => flere ting ? tenke p? hver dag eller to!
[5] => Dal?? v?c?, p?em??let o ka?d? den nebo dva!
[6] => mehr ?ber Spass sp?t sch?nen
[7] => m? von? gjat? fun bukur
[8] => t?bb mint sz?rakoz?s k?s? csod?latos keny?r
)

This might be of interest when trying to convert utf-8 strings into ASCII suitable for URL's, and such. this was never obvious for me since I've used locales for us and nl.
up
-6
jaaks at playtech dot com
19 years ago
Last example for verifying UTF-8 has one little bug. If 10xxxxxx byte occurs alone i.e. not in multibyte char, then it is accepted although it is against UTF-8 rules. Make following replacement to repair it.

Replace
} // goto next char
with
} else {
return false; // 10xxxxxx occuring alone
} // goto next char
up
-12
prgss at bk dot ru
14 years ago
Another light way to detect character encoding:
<?php
function detect_encoding($string) {
static
$list = array('utf-8', 'windows-1251');

foreach (
$list as $item) {
$sample = iconv($item, $item, $string);
if (
md5($sample) == md5($string))
return
$item;
}
return
null;
}
?>
up
-16
sunggsun
17 years ago
from PHPDIG

function isUTF8($str) {
if ($str === mb_convert_encoding(mb_convert_encoding($str, "UTF-32", "UTF-8"), "UTF-8", "UTF-32")) {
return true;
} else {
return false;
}
}
To Top