Briefly introduce the difference between strlen and mb_strlen in php

Commonly used functions in php to calculate string length are: strlen and mb_strlen. When the characters are all English characters, the two are Same. Here we mainly compare the two calculation results when Chinese and English are mixed.

In PHP, strlen and mb_strlen are functions to find the length of a string, but for some beginners, if they don’t read the manual, they may not be clear about the difference.
The following is an example to explain the difference between the two.

Look at the example first:

<?php 
//测试时文件的编码方式要是UTF8 
$str=&#39;中文a字1符&#39;; 
echo strlen($str).&#39;<br>&#39;;//14 
echo mb_strlen($str,&#39;utf8&#39;).&#39;<br>&#39;;//6 
echo mb_strlen($str,&#39;gbk&#39;).&#39;<br>&#39;;//8 
echo mb_strlen($str,&#39;gb2312&#39;).&#39;<br>&#39;;//10 
?>

Result analysis: When calculating strlen, a UTF8 Chinese character is treated as 3 lengths, so the length of "Chinese a character 1 character" is 3*4+ 2=14. When calculating mb_strlen, if the internal code is selected as UTF8, a Chinese character will be calculated as a length of 1, so the length of "Chinese a character 1 character" is 6.

Use these two A function can jointly calculate the occupancy of a mixed Chinese and English string (the occupancy of a Chinese character is 2, and the occupancy of an English character is 1)

echo (strlen($str) + mb_strlen($str,'UTF8')) / 2;

For example, "Chinese a character 1 character" The value of strlen($str) is 14, and the value of mb_strlen($str) is 6. Then it can be calculated that the placeholder for "Chinese a character 1 character" is 10.

echo mb_internal_encoding();

PHP's built-in string length function strlen Doesn't handle Chinese strings correctly, all it gets is the number of bytes occupied by the string. For GB2312 Chinese encoding, the value obtained by strlen is twice the number of Chinese characters, while for UTF-8 encoded Chinese, the difference is three times (under UTF-8 encoding, one Chinese character occupies 3 bytes).

Using the mb_strlen function can better solve this problem. The usage of mb_strlen is similar to strlen, except that it has a second optional parameter to specify the character encoding. For example, to get the UTF-8 string $str length, you can use mb_strlen($str,'UTF-8'). If the second parameter is omitted, PHP's internal encoding will be used. The internal encoding can be obtained through the mb_internal_encoding() function.

It should be noted that mb_strlen is not a core function of PHP. Before using it, you need to make sure that php_mbstring.dll is loaded in php.ini, that is, make sure that "extension=php_mbstring.dll" A line exists and is not commented, otherwise an undefined function problem will occur.

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