PHP Manual: mb

function mb_strlen(string $string, ?string $encoding = null): int

Gets the length of a string.

string: The string being checked for length.
encoding: The encoding parameter is the character encoding. If it is omitted or null, the internal character encoding value will be used.

Returns the number of characters in string string having character encoding encoding. A multi-byte character is counted as 1.

As of PHP 8.0.0, a ValueError is thrown if encoding is an invalid encoding. Prior to PHP 8.0.0, an E_WARNING was emitted instead.

Version	Description
8.0.0	`encoding` is nullable now.
8.0.0	Now throws a ValueError if `encoding` is an invalid encoding. Previously, an `E_WARNING` was emitted and `false` was returned.

mb_strlen