Detailed explanation of the difference between strlen and mb_strlen functions in PHP

Detailed explanation of the difference between strlen and mb_strlen functions in PHP_PHP Tutorial

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Release： 2016-07-13 10:37:15

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There are two functions for calculating the number of strings in PHP
One is strlen and the other is mb_strlen;
Let’s first look at the definition in the manual
strlen
strlen — Get the length of a string
int strlen ( string $string )
Returns the length of the given string string.

mb_strlen
int mb_strlen ( string $str [, string $encoding ] )
Returns the length of the given string string.
The encoding parameter is character encoding. If omitted, the internal character encoding is used.

It seems that there is no other difference except that mb_strlen can pass a character encoding. The following is an example to explain the difference between the two.
Look at the example first:

Copy the code The code is as follows:

$str='Chinese a character 1 character';
echo strlen($str).'
';//14 str,'utf8').'
';//6
echo mb_strlen($str,'gbk').'
';//8
echo mb_strlen($str, 'gb2312').'
';//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 to be UTF8, a Chinese character will be calculated as a length of 1, so "Chinese a character 1 character" The length is 6.
Using these two functions, you 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)

Copy code The code is as follows:

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

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

Copy code The code is as follows:

echo mb_internal_encoding();

PHP’s built-in string length function strlen cannot 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 under Windows, you need to make sure that php_mbstring.dll is loaded in php.ini, that is, make sure that the line "extension=php_mbstring.dll" exists and has not been commented out. Otherwise, undefined function problems will occur. This extension needs to be compiled under Linux.