PHP 判斷字符串是否純漢字

function xmsb_checkString($str = '')
{
    $return = [];
    $return['msg'] = '英文、漢字混合字符串';
    $return['code'] = 0;
    
    if(!is_string($str) || trim($str) == '')
    {
        trigger_error('xmsb_checkString() 參數1必須為一個非空字符串', E_USER_ERROR);
    }
    else
    {
        $mbLen = mb_strlen($str, 'utf-8');
        $noLen = strlen($str);
        
        if($mbLen == $noLen)
        {
            $return['msg'] = '純英文字符串';
            $return['code'] = 1;
        }
        else if($noLen / $mbLen == 3)
        {
            $return['msg'] = '純漢字字符串';
            $return['code'] = 2;
        }
    }
    
    return $return;
}