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

mb_substr() is a PHP string function that can cut a part of a multibyte string and return the new string. Unlike substr(), mb_substr() correctly handles multibyte characters (e.g., Chinese, Japanese) ensuring no garbled output.

mb_substr() function syntax

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

Where $str is the input string, $start is the starting position (0‑based), $length is the length to cut, and $encoding is the character encoding (default is the script’s encoding, usually UTF‑8).

Usage examples

Example 1

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

Because Chinese characters occupy two bytes, cutting the first two characters yields "今天".

Example 2

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

Since Chinese characters are two bytes, extracting four characters starting from position 1 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 returns the substring from the start position to 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 substring extends to the end.

When building multilingual websites, mb_substr() is convenient for correctly handling multibyte characters without affecting page display.

Overall, mb_substr() is a practical PHP function for safely cutting multibyte strings, essential for developers working on internationalized projects.