Mastering PHP’s mb_substr: Handle Multibyte Strings with Ease

mb_substr()

is a PHP string function that extracts a portion of a multibyte string, correctly handling characters such as Chinese or Japanese, unlike substr(). This ensures the resulting substring is not garbled.

mb_substr() function signature

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

The parameters are: $str: the input string to be cut. $start: the starting position (0‑based). $length: the length to extract (optional). $encoding: 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, extracting the first two characters yields “今天”.

Example 2

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

Again, Chinese characters take two bytes, so 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 argument is omitted, the function extracts to the end of the string.

Note that if $start exceeds the string length, mb_substr() returns an empty string. A negative $length is ignored and the substring runs to the end.

When building multilingual websites, mb_substr() is indispensable for correctly handling multibyte characters without breaking page layout.