5 ways to detect whether a string encoding is UTF8 in PHP

function mb_is_utf8($string)
{
    return mb_detect_encoding($string, 'UTF-8') === 'UTF-8';//新发现
}

方法二：

function preg_is_utf8($string)
{
    return preg_match('/^.*$/u', $string) > 0;//preg_match('/^./u', $string)
}

方法三：

function is_utf8_1($str)
{
    $c=0; $b=0;
    $bits=0;
    $len=strlen($str);
    for($i=0; $i<$len; $i++){
        $c=ord($str[$i]);
        if($c > 128){  // bbs.it-home.org
            if(($c >= 254)) return false;
            elseif($c >= 252) $bits=6;
            elseif($c >= 248) $bits=5;
            elseif($c >= 240) $bits=4;
            elseif($c >= 224) $bits=3;
            elseif($c >= 192) $bits=2;
            else return false;
            if(($i+$bits) > $len) return false;
            while($bits > 1){
                $i++;
                $b=ord($str[$i]);
                if($b < 128 || $b > 191) return false;
                $bits--;
            }
        }
    }
    return true;
}

方法四：

function is_utf8_2($string) {

    // From http://w3.org/International/questions/qa-forms-utf-8.html
    return preg_match('%^(?:
          [x09x0Ax0Dx20-x7E]            # ASCII
        | [xC2-xDF][x80-xBF]             # non-overlong 2-byte
        |  xE0[xA0-xBF][x80-xBF]        # excluding overlongs
        | [xE1-xECxEExEF][x80-xBF]{2}  # straight 3-byte
        |  xED[x80-x9F][x80-xBF]        # excluding surrogates
        |  xF0[x90-xBF][x80-xBF]{2}     # planes 1-3
        | [xF1-xF3][x80-xBF]{3}          # planes 4-15
        |  xF4[x80-x8F][x80-xBF]{2}     # plane 16
    )*$%xs', $string);

} // function is_utf8

方法五：

function isUTF8($string)
{
    return (utf8_encode(utf8_decode($string)) == $string);
}