Master PHP’s mb_strlen: Accurately Measure Multibyte String Lengths

When working with multibyte characters such as Chinese or Japanese, the standard PHP string functions fall short, so the mb_strlen() function from the mbstring extension is used to obtain the correct length of multibyte strings.

Before using mb_strlen(), ensure the mbstring extension is installed and enabled. This can be done by removing the comment in php.ini or confirming activation with phpinfo().

The function signature is:

int mb_strlen ( string $str [, string $encoding = mb_internal_encoding() ] )

$str

is the target multibyte string, and $encoding is optional; if omitted, the encoding returned by mb_internal_encoding() is used.

Example 1 – Chinese string

<?php
$str = "你好，世界！";
echo mb_strlen($str); // Output: 7
?>

The string contains four Chinese characters and three ASCII characters, resulting in a length of 7.

Example 2 – UTF‑8 Japanese string

<?php
$str = "こんにちは世界";
echo mb_strlen($str, "UTF-8"); // Output: 6
?>

Specifying the UTF‑8 encoding, the function counts three Japanese characters and three Chinese characters, yielding a length of 6.

Example 3 – Length validation

<?php
$str = "This is a very long sentence.";
$max_length = 20;
if (mb_strlen($str) > $max_length) {
    echo "String is too long.";
} else {
    echo "String is within the limit.";
}
?>

This snippet demonstrates how to enforce a maximum length constraint using mb_strlen().

In summary, mb_strlen() provides a reliable way to obtain the length of multibyte strings, optionally specify character encoding, and perform length checks, helping developers handle international text accurately and improve program stability.