php 怎么处理 非 utf-8 编码的文件？

public function detect_utf_encoding($filename){        
        if( 'UTF-16LE' === $this->utf_encoding( $filename )){
            return iconv('UTF-16', 'UTF-8', file_get_contents( $filename ));
        }else {
            return file_get_contents( $filename );
        }
}

public function utf_encoding($filename) {

    $utf32_big_bom = chr(0x00) . chr(0x00) . chr(0xFE) . chr(0xFF);
    $utf32_little_bom = chr(0xFF) . chr(0xFE) . chr(0x00) . chr(0x00);
    $utf16_big_bom = chr(0xFE) . chr(0xFF);
    $utf16_little_bom = chr(0xFF) . chr(0xFE);
    $utf8_bom = chr(0xEF) . chr(0xBB) . chr(0xBF);

    $text = file_get_contents($filename);
    $first2 = substr($text, 0, 2);
    $first3 = substr($text, 0, 3);
    $first4 = substr($text, 0, 3);

    if ($first3 == $utf8_bom)
    return 'UTF-8';
        elseif ($first4 == $utf32_big_bom)
            return 'UTF-32BE';
        elseif ($first4 == $utf32_little_bom)
            return 'UTF-32LE';
        elseif ($first2 == $utf16_big_bom)
            return 'UTF-16BE';
        elseif ($first2 == $utf16_little_bom)
            return 'UTF-16LE';
}

可参考如下方式转换：

$str = file_get_contents('filename.txt');
$str = mb_convert_encoding($str, "UTF-8", "GBK");
var_dump($str);