$str = "中文字及english測試"; echo strlen($str) . "<br />"; echo mb_strlen($str, 'UTF-8') . "<br />"; echo mb_strlen($str, 'UTF8') . "<br />"; echo mb_strwidth($str, 'UTF-8') . "<br />"; echo mb_substr($str, 2, 4, 'UTF-8') . "<br />";

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Result:
25
13
13
19
字及en