php判断字符串编码函数

//判断字符串是什么编码
if ($tag === mb_convert_encoding(mb_convert_encoding($tag, "GB2312", "UTF-8"), "UTF-8", "GB2312")) {

}
else {//如果是gb2312 的就转换为utf8的
$tag = mb_convert_encoding($tag, 'UTF-8', 'GB2312');
}

/**
 +----------------------------------------------------------
 * 检查字符串是否是UTF8编码
 +----------------------------------------------------------
 * @param string $string 字符串
 +----------------------------------------------------------
 * @return Boolean
 +----------------------------------------------------------
 */
function is_utf8($string)
{
    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_gb2312($str)
{
        for($i=0; $i                 $v = ord( $str[$i] );
                if( $v > 127) {
                        if( ($v >= 228) && ($v <= 233) )
                        {
                                if( ($i+2) >= (strlen($str) - 1)) return true;  // not enough

characters
                                $v1 = ord( $str[$i+1] );
                                $v2 = ord( $str[$i+2] );
                                if( ($v1 >= 128) && ($v1 <=191) && ($v2 >=128) && ($v2 <= 191) ) // utf

编码
                                        return false;
                                else
                                        return true;
                        }
                }
        }
        return true;
}