mb_detect_encoding()

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

检测字符的编码

说明

mb_detect_encoding (string $str[, mixed $encoding_list= mb_detect_order() [,bool $strict= false ]] ) : string

检测字符串$str的编码。

参数

$str

待检查的字符串。

$encoding_list

$encoding_list是一个字符编码列表。编码顺序可以由数组或者逗号分隔的列表字符串指定。

如果省略了$encoding_list将会使用 detect_order。

$strict

$strict指定了是否严格地检测编码。默认是 FALSE。

返回值

检测到的字符编码，或者无法检测指定字符串的编码时返回 FALSE。

范例

mb_detect_encoding() 例子

<?php
/* 使用当前的 detect_order 来检测字符编码 */
echo mb_detect_encoding($str);
/* "auto" 将根据 mbstring.language 来扩展 */
echo mb_detect_encoding($str, "auto");
/* 通过逗号分隔的列表来指定编码列表 encoding_list */
echo mb_detect_encoding($str, "JIS, eucjp-win, sjis-win");
/* 使用数组来指定编码列表 encoding_list  */
$ary[] = "ASCII";
$ary[] = "JIS";
$ary[] = "EUC-JP";
echo mb_detect_encoding($str, $ary);
?>

参见

mb_detect_order()设置/获取字符编码的检测顺序

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
?>

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.

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);
}
?>

Beware of bug to detect Russian encodings
http://bugs.php.net/bug.php?id=38138

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).

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';
}
?>

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.

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;
}
?>

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
 }

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);

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
?>

For detect UTF-8, you can use:
if (preg_match('!!u', $str)) { echo 'utf-8'; }
- Norihiori

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

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('accentue' , '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

// ----------------------------------------------------------- 
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;
}
}
// -----------------------------------------------------------

<?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;
}
}
?>

<?php
$file = file_get_contents("somefile.txt");
$encodings = implode(',', mb_list_encodings());
echo mb_detect_encoding($file, $encodings, true);
?>
seems to work

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

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!

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.

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

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;
    }
  }

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;
}
?>