Master Multibyte String Cutting in PHP with mb_substr – Examples & Tips

The mb_substr() function is a PHP string truncation function that can cut a portion of a multibyte string and return the new string. Unlike the regular substr() function, mb_substr() correctly handles multibyte characters (such as Chinese, Japanese, etc.), ensuring that the resulting string is not garbled or inaccurately cut. This is useful for internationalized projects.

mb_substr() function syntax:

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

Usage examples:

Example 1:

$str = "今天是个好日子";
echo mb_substr($str, 0, 2); // outputs "今天"

Since Chinese characters occupy 2 bytes, cutting the first 2 characters yields "今天".

Example 2:

$str = "abcdefg你好";
echo mb_substr($str, 1, 4); // outputs "bcde"

Because Chinese characters occupy 2 bytes, cutting 4 characters starting from the second character gives "bcde".

Example 3:

$str = "abcdefg你好";
echo mb_substr($str, 4); // outputs "g你好"

If the length parameter is omitted, the function extracts until the end of the string.

Note that if $start exceeds the string length, mb_substr() returns an empty string. If $length is negative, it is ignored and the function extracts to the end.

When building multilingual websites, mb_substr() is convenient because it correctly handles multibyte characters without affecting page display.

Overall, mb_substr() is a practical PHP string function that reliably processes multibyte encoded characters such as Chinese and Japanese, making it essential for developers working on internationalized projects.