mb_strlen

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

mb_strlen — 获取字符串的长度

说明

mb_strlen ( string $str , string $encoding = mb_internal_encoding() ) : mixed

获取一个 string 的长度。

参数

str: 要检查长度的字符串。
encoding: encoding 参数为字符编码。如果省略或是 null，则使用内部字符编码。

返回值

返回具有 encoding 编码的字符串 str 包含的字符数。多字节的字符被计为 1。

如果给定的 encoding 无效则返回 false。

参见

mb_internal_encoding() - 设置/获取内部字符编码
grapheme_strlen() - Get string length in grapheme units
iconv_strlen() - 返回字符串的字符数统计
strlen() - 获取字符串长度

User Contributed Notes

David Spector 08-Jan-2020 11:19


It may not be clear whether PHP actually supports utf-8, which is the current de facto standard character encoding for Web documents, which supports most human languages. The good news is: it does.



I wrote a test program which successfully reads in a utf-8 file (without BOM) and manipulates the characters using mb_substr, mb_strlen, and mb_strpos (mb_substr should normally be avoided, as it must always start its search at character position 0).



The results with a variety of Unicode test characters in utf-8 encoding, up to four bytes in length, were mostly correct, except that accent marks were always mistakenly treated as separate characters instead of being combined with the previous character; this problem can be worked around by programming, when necessary.

Yzmir Ramirez 15-Apr-2011 09:06


If you are unsure about what $encoding can be set to, here's a full list of all the encodings supported by this extension:



http://www.php.net/manual/en/mbstring.supported-encodings.php

Ben 19-Nov-2008 02:59


If you find yourself without the mb string functions and can't easily change it, a quick hack replacement for mb_strlen for utf8 characters is to use a a PCRE regex with utf8 turned on.



$strlen = preg_match_all("/.{1}/us",$utf8string,$dummy);



This is basically an ugly hack which counts all single character matches, and I'd expect it to be painfully slow on large strings.

drake127 12-Aug-2007 08:36


Speed of mb_strlen varies a lot according to specified character set.



If you need length of string in bytes (strlen cannot be trusted anymore because of mbstring.func_overload) you should use <?php mb_strlen($string, '8bit'); ?>.

It's the fastest way (still a way slower than strlen, though) to determine byte length of string. Other single byte character sets (ASCII, ISO-8859-1, ...) are several times slower than 8bit.

koala at example dot com 27-Jul-2007 12:19


Just did a little benchmarking (1.000.000 times with lorem ipsum text) on the mbs functions



especially mb_strtolower and mb_strtoupper are really slow (up to 100 times slower compared to normal functions). Other functions are alike-ish, but sometimes up to 5 times slower.



just be cautious when using mb_ functions in high frequented scripts.



# test runs: 1000000

# benchmarking strlen vs. mb_strlen

# normal strlen: 3.6795361042023 ms, average: 3.6795361042023E-6 ms

# mb_strlen: 5.5934538841248 ms, average: 5.5934538841248E-6 ms

ok 1 - mb_strlen is slower than strlen

# mb_strlen is 1.52 slower than strlen

#

#

# benchmarking strpos vs. mb_strpos

# normal strpos: 5.5523281097412 ms, average: 5.5523281097412E-6 ms

# mb_strlen: 31.180974960327 ms, average: 3.1180974960327E-5 ms

ok 2 - mb_strlen is slower than strlen

# mb_strpos is 5.62 slower than strpos

#

#

# benchmarking substr vs. mb_substr

# normal substr: 3.4437320232391 ms, average: 3.4437320232391E-6 ms

# mb_strlen: 3.5374181270599 ms, average: 3.5374181270599E-6 ms

ok 3 - mb_strlen is slower than strlen

# mb_substr is 1.03 slower than substr

#

#

# benchmarking strtolower vs. mb_strtolower

# normal strtolower: 4.446839094162 ms, average: 4.446839094162E-6 ms

# mb_strlen: 193.44901108742 ms, average: 0.00019344901108742 ms

ok 4 - mb_strlen is slower than strlen

# mb_strtolower is 43.5 slower than strtolower

#

#

# benchmarking strtoupper vs. mb_strtoupper

# normal strtoupper: 3.0210740566254 ms, average: 3.0210740566254E-6 ms

# mb_strlen: 340.71775603294 ms, average: 0.00034071775603294 ms

ok 5 - mb_strlen is slower than strlen

# mb_strtoupper is 112.78 slower than strtoupper

motin at demomusic dot nu 06-Feb-2007 10:12


Thank you Peter Albertsson for presenting that!



After spending more than eight hours tracking down two specific bugs in my mbstring-func_overloaded environment I have learned a very important lesson:



Many developers rely on strlen to give the amount of bytes in a string. While mb-overloading has very many advantages, the most hard-spotted pitfall must be this issue. 



Two examples (from the two bugs found earlier):



1. Writing a string to a file:



<?php

$str = "string with utf-8 chars ?è? - doo-bee doo-bee dooh";

$fp = fopen($this->_file, "wb");

if ($fp) {

  $len = strlen($str);

  fwrite($fp, $str, $len);

}

?>



PS This is found i the PEAR::Cache_Lite package (Lite.php) - Reported



2. Iterating through a string's characters:



<?php

$str = "string with utf-8 chars ?è? - doo-bee doo-bee dooh";

$newStr = "";

for ($i = 0; $i < strlen($str); $i++) {

  $newStr .= $str[$i];

}

?>



Both of these situations will fail to save / store the last characters in $str. This can be very hard to spot and can be especially fatal for say serialized strings, xml etc. 



So, try to avoid these situations to support overloaded environments, and remeber Peter Albertssons remark if you find problems under such an environment.

filatei at gmail dot com 12-Aug-2006 10:48


I have been working with some funny html characters lately and due to the nightmare in manipulating them between mysql and php, I got the database column set to utf8, then store characters with html enity "&#7885;" as ? in the database and set the encoding on php as "utf8".



This is where mb_strlen became more useful than strlen.  While strlen('?') gives result as 3, mb_strlen('?','UTF-8') gives 1 as expected.



But left(column1,1) in mysql still gives wrong char for a multibyte string.  In the example above, I had to do left(column1,3) to get the correct string from mysql.  I am now about to investigate multibyte manipulation in mysql.