International PHP Conference 2015

mb_substr

(PHP 4 >= 4.0.6, PHP 5)

mb_substr文字列の一部を得る

説明

string mb_substr ( string $str , int $start [, int $length = NULL [, string $encoding = mb_internal_encoding() ]] )

文字数に基づきマルチバイト対応の substr() 処理を行います。位置は、 str の始めから数えられます。 最初の文字の位置は 0、2 番目の文字の位置は 1、といったようになります。

パラメータ

str

部分文字列を取り出したい文字列。

start

start が非負である場合に返される文字列は、 stringstart バイト目以降の文字列となります (ゼロから数えます)。 たとえば、文字列 'abcdef' の 0 バイト目は 'a' で、 2 バイト目は 'c' のようになります。

start が負の数の場合に返される文字列は、 string の後ろから数えて start バイト目以降となります。

length

str の中から取り出す最大文字数。 省略したり NULL を渡したりした場合は、 文字列の最後までの全バイトを取り出します。

encoding

encoding パラメータには文字エンコーディングを指定します。省略した場合は、 内部文字エンコーディングを使用します。

返り値

mb_substr() は、start および length パラメータで指定した str の一部を返します。

変更履歴

バージョン 説明
5.4.8 lengthNULL を渡すと、文字列の末尾までのすべてのバイトを取り出すようになりました。 これより前のバージョンでは、NULL0 と同じ扱いでした。

参考

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User Contributed Notes 10 notes

up
22
Silvan
8 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
3
xiaogil at yahoo dot fr
10 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
Anonymous
5 years ago
If start  is negative, the returned string will start at the start'th character from the end of string
up
0
qbolec at gmail dot com
29 days 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($text) split the text recursively into two parts. Each level of the recursion requires time linear in the length of the string, and there is logarithmic number of levels, so the total runtime is O(N log N), which is still more than theoretically optimal O(N), but sadly this is the best idea I've got.
up
0
247hastings at gmail dot com
8 months ago
Starting in PHP 5.4.8 passing a null as a default value to mb_substr() and mb_strcut() will work as expected.
up
0
desmatic at gmail dot com
2 years ago
quick and dirty loop through multibyte string
<?php
function get_character_classes($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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0
p dot assenov at aip-solutions dot com
3 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
0
drraf at tlen dot pl
10 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
-4
projektas at gmail dot com
6 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>
up
-2
sanjuro at 1up-games dot com
1 year 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>

?>
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