mb_substr

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

mb_substrGet part of string

Beschreibung

mb_substr(
    string $string,
    int $start,
    ?int $length = null,
    ?string $encoding = null
): string

Performs a multi-byte safe substr() operation based on number of characters. Position is counted from the beginning of string. First character's position is 0. Second character position is 1, and so on.

Parameter-Liste

string

The string to extract the substring from.

start

If start is non-negative, the returned string will start at the start'th position in string, counting from zero. For instance, in the string 'abcdef', the character at position 0 is 'a', the character at position 2 is 'c', and so forth.

If start is negative, the returned string will start at the start'th character from the end of string.

length

Maximum number of characters to use from string. If omitted or NULL is passed, extract all characters to the end of the string.

encoding

Der Parameter encoding legt die Zeichenkodierung fest. Wird er nicht übergeben, so wird die interne Zeichenkodierung genutzt.

Rückgabewerte

mb_substr() returns the portion of string specified by the start and length parameters.

Changelog

Version Beschreibung
8.0.0 encoding ist nun nullable (akzeptiert den null-Wert).

Siehe auch

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User Contributed Notes 9 notes

up
48
Silvan
16 years ago
Passing null as length will not make mb_substr use it's default, instead it will interpret it as 0.
<?php
mb_substr
($str,$start,null,$encoding); //Returns '' (empty string) just like substr()
?>
Instead use:
<?php
mb_substr
($str,$start,mb_strlen($str),$encoding);
?>
up
8
qbolec at gmail dot com
8 years ago
As you often need to iterate over UTF-8 characters inside a string, you might be tempted to use mb_substr($text,$i,1).
The problem with this is that there is no "magic" way to find $i-th character inside UTF-8 string, other than reading it byte by byte from the begining. Thus a loop which calls mb_substr($text,$i,1) N times for all possible N values of $i, will take much longer than expected. The larger the $i gets, the longer is the search for $i-th letter. As characters are between 1 to 6 bytes long, one can convince oneself, that the execution time of such loop is actually Theta(N^2), which can be really slow even for moderately long texts.
One way to work around it is to first split your text into an array of letters using some smart preprocessing, and only then iterate over the array.
Here is the idea:
<?php
class Strings
{
  public static function
len($a){
    return
mb_strlen($a,'UTF-8');
  }
  public static function
charAt($a,$i){
    return
self::substr($a,$i,1);
  }
  public static function
substr($a,$x,$y=null){
    if(
$y===NULL){
     
$y=self::len($a);
    }
    return
mb_substr($a,$x,$y,'UTF-8');
  }
  public static function
letters($a){
   
$len = self::len($a);
    if(
$len==0){
      return array();
    }else if(
$len == 1){
      return array(
$a);
    }else{
      return
Arrays::concat(
       
self::letters(self::substr($a,0,$len>>1)),
       
self::letters(self::substr($a,$len>>1))
      );
    }
  }
?>
As you can see, the Strings::letters($text) split the text recursively into two parts. Each level of the recursion requires time linear in the length of the string, and there is logarithmic number of levels, so the total runtime is O(N log N), which is still more than theoretically optimal O(N), but sadly this is the best idea I've got.
up
4
xiaogil at yahoo dot fr
18 years ago
Thanks Darien from /freenode #php for the following example (a little bit changed).

It just prints the 6th character of $string.
You can replace the digits by the same in japanese, chinese or whatever language to make a test, it works perfect.

<?php
mb_internal_encoding
("UTF-8");
$string = "0123456789";
$mystring = mb_substr($string,5,1);
echo
$mystring;
?>

(I couldn't replace 0123456789 by chinese numbers for example here, because it's automatically converted into latin digits on this website, look :
&#38646;&#19968;&#20108;&#19977;&#22235;
&#20116;&#20845;&#19971;&#20843;&#20061;)

gilv
up
2
drraf at tlen dot pl
19 years ago
Note: If borders are out of string - mb_string() returns empty _string_, when function substr() returns _boolean_ false in this case.
Keep this in mind when using "===" comparisions.

Example code:
<?php

var_dump
( substr( 'abc', 5, 2 ) ); // returns "false"
var_dump( mb_substr( 'abc', 5, 2 ) ); // returns ""

?>

It's especially confusing when using mbstring with function overloading turned on.
up
0
desmatic at gmail dot com
10 years ago
quick and dirty loop through multibyte string
<?php
function get_character_classes($string, $encoding = "UTF-8") {
   
$current_encoding = mb_internal_encoding();
   
mb_internal_encoding($encoding);
   
$has = array();
   
$stringlength = mb_strlen($string, $encoding);
    for (
$i=0; $i < $stringlength; $i++) {
       
$c = mb_substr($string, $i, 1);
        if ((
$c >= "0") && ($c <= "9")) {
           
$has['numeric'] = "numeric";
        } else if ((
$c >= "a") && ($c <= "z")) {
           
$has['alpha'] = "alpha";
           
$has['alphalower'] = 'alphalower';
        } else if ((
$c >= "A") && ($c <= "Z")) {
           
$has['alpha'] = "alpha";
           
$has['alphaupper'] = "alphaupper";
        } else if ((
$c == "$") || ($c == "£")) {
           
$has['currency'] = "currency";
        } else if ((
$c == ".") && ($has['decimal'])) {
           
$has['decimals'] = "decimals";
        } else if (
$c == ".") {
           
$has['decimal'] = "decimal";
        } else if (
$c == ",") {
           
$has['comma'] = "comma";
        } else if (
$c == "-") {
           
$has['dash'] = "dash";
        } else if (
$c == " ") {
           
$has['space'] = "space";
        } else if (
$c == "/") {
           
$has['slash'] = "slash";
        } else if (
$c == ":") {
           
$has['colon'] = "colon";
        } else if ((
$c >= " ") && ($c <= "~")) {
           
$has['ascii'] = "ascii";
        } else {
           
$has['binary'] = "binary";
        }
    }
   
mb_internal_encoding($current_encoding);
   
    return
$has;
}

$string = "1234asdfA£^_{}|}~žščř";
echo
print_r(get_character_classes($string), true);
?>

Array
(
    [numeric] => numeric
    [alpha] => alpha
    [alphalower] => alphalower
    [alphaupper] => alphaupper
    [currency] => currency
    [ascii] => ascii
    [binary] => binary
)
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-1
p dot assenov at aip-solutions dot com
12 years ago
I'm trying to capitalize only the first character of the string and tried some of the examples above but they didn't work. It seems mb_substr() cannot calculate the length of the string in multi-byte encoding (UTF-8) and it should be set explicitly. Here is the corrected version:

<?php
function mb_ucfirst($str, $enc = 'utf-8') {
    return
mb_strtoupper(mb_substr($str, 0, 1, $enc), $enc).mb_substr($str, 1, mb_strlen($str, $enc), $enc);
}
?>

cheers!
up
-4
qdinar at gmail dot com
7 years ago
you can make mb_substr working faster with long strings with usage of ucs-2 encoding.

<?php

header
('Content-Type: text/html; charset=utf-8');
echo
'<meta http-equiv="Content-Type" content="text/html; charset=utf-8" >';

function
test($string, $encoding='utf8'){
   
$t1=microtime(true);
   
$textlen=mb_strlen($string);
   
$substr_len=3;
    for(
$i=0;$i<$textlen-$substr_len+1;$i++){
       
$substr=mb_substr($string,$i,$substr_len);
    }
    echo
'mb_substr, '.$encoding.': '.(microtime(true)-$t1);
    echo
' . check: ';
    if(
$encoding=='ucs2'){
       
$substr=mb_convert_encoding($substr,'utf-8','ucs2');
    }
   
var_dump( $substr );
    echo
' . <br>';
    echo
'<br>';
}

$corpus_short=str_repeat('тест Тест ',1000);
// it works likewise slowly with "test Test" with utf8
mb_internal_encoding('utf-8');
test($corpus_short);

$corpus_short_ucs2=mb_convert_encoding($corpus_short,'ucs2','utf-8');
mb_internal_encoding('ucs2');
test($corpus_short_ucs2,'ucs2');

?>

output:

mb_substr, utf8: 0.26480984687805 . check: string(5) "ст " .

mb_substr, ucs2: 0.0048871040344238 . check: string(5) "ст " .
up
-5
sanjuro at 1up-games dot com
10 years ago
A serious pitfall when using mb_substr() set to HTML-ENTITIES encoding is that the function performs a number of conversions before returning the value, the worst one being that html special characters are not just counted but decoded.

<?php

mb_internal_encoding
("ISO-8859-1"); echo mb_internal_encoding(),"\n<br><br>\n";

$a='j&uuml;st &#228; &quot; simple &quot; &#26085;&#26412; &lt;b&gt;test&lt;/b&gt;';

echo
mb_substr($a,0),"\n<br><br>\n";
// page source: j&uuml;st &#228; &quot; simple &quot; &#26085;&#26412; &lt;b&gt;test&lt;/b&gt;

echo mb_substr($a,0,strlen($a),'HTML-ENTITIES');
// page source: j&uuml;st &auml; " simple " &#26085;&#26412; <b>test</b>

?>
up
-15
projektas at gmail dot com
15 years ago
First letter in upper case <hr />

<?php
header
('Content-type: text/html; charset=utf-8');

if (isset(
$_POST['check']) && !empty($_POST['check'])) {
    echo
htmlspecialchars(ucfirst_utf8($_POST['check']));
} else {
    echo
htmlspecialchars(ucfirst_utf8('Žąsinų'));
}

function
ucfirst_utf8($str) {
    if (
mb_check_encoding($str,'UTF-8')) {
       
$first = mb_substr(
           
mb_strtoupper($str, "utf-8"),0,1,'utf-8'
       
);
        return
$first.mb_substr(
           
mb_strtolower($str,"utf-8"),1,mb_strlen($str),'utf-8'
       
);
    } else {
        return
$str;
    }
}
?>

<form method="post" action="" >
    <input type="input" name="check" />
    <input type="submit" />
</form>
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