php字符串截取，支持中文和其他编码

/**
 * 字符串截取，支持中文和其他编码
 *
 * @static
 * @access public
 * @param string $str 需要转换的字符串
 * @param string $start 开始位置
 * @param string $length 截取长度
 * @param string $charset 编码格式
 * @param string $suffix 截断显示字符
 * @return string
 */
function msubstr($str, $start=0, $length, $charset="utf-8", $suffix=true)
{
    if(function_exists("mb_substr"))
         mb_substr($str, $start, $length, $charset);
    elseif(function_exists('iconv_substr')) {
         iconv_substr($str,$start,$length,$charset);
    }
    $re['utf-8']   = "/[x01-x7f]|[xc2-xdf][x80-xbf]|[xe0-xef][x80-xbf]{2}|[xf0-xff][x80-xbf]{3}/";
    $re['gb2312'] = "/[x01-x7f]|[xb0-xf7][xa0-xfe]/";
    $re['gbk']    = "/[x01-x7f]|[x81-xfe][x40-xfe]/";
    $re['big5']   = "/[x01-x7f]|[x81-xfe]([x40-x7e]|xa1-xfe])/";
    preg_match_all($re[$charset], $str, $match);
    $slice = join("",array_slice($match[0], $start, $length));
    if($suffix) return $slice."…";
    return $slice;
}

function msubstr($str, $start, $len) {
    $tmpstr = "";
    $strlen = $start + $len;
    for($i = 0; $i < $strlen; $i++) {
        if(ord(substr($str, $i, 1)) > 0xa0) {
            $tmpstr .= substr($str, $i, 2);
            $i++;
        } else
            $tmpstr .= substr($str, $i, 1);
    }
    return $tmpstr;
}