正则例子:
preg_replace("/([\x80-\xff])/","",$str);
preg_replace("/([u4e00-u9fa5])/","",$str);

二、代码例子

//判断内容里有没有中文-GBK (PHP)
function check_is_chinese($s){
    return preg_match('/[\x80-\xff]./', $s);
}

//获取字符串长度-GBK (PHP)
function gb_strlen($str){
    $count = 0;
    for($i=0; $i<strlen($str); $i++){
        $s = substr($str, $i, 1);
        if (preg_match("/[\x80-\xff]/", $s)) ++$i;
        ++$count;
    }
    return $count;
}

//截取字符串字串-GBK (PHP)
function gb_substr($str, $len){
    $count = 0;
    for($i=0; $i<strlen($str); $i++){
        if($count == $len) break;
        if(preg_match("/[\x80-\xff]/", substr($str, $i, 1))) ++$i;
        ++$count;       
    }
    return substr($str, 0, $i);
}

//统计字符串长度-UTF8 (PHP)
function utf8_strlen($str) {
    $count = 0;
    for($i = 0; $i < strlen($str); $i++){
        $value = ord($str[$i]);
        if($value > 127) {
            $count++;
            if($value >= 192 && $value <= 223) $i++;
            elseif($value >= 224 && $value <= 239) $i = $i + 2;
            elseif($value >= 240 && $value <= 247) $i = $i + 3;
            else die('Not a UTF-8 compatible string');
        }
        $count++;
    }
    return $count;
}

//截取字符串-UTF8(PHP)
function utf8_substr($str,$position,$length){
    $start_position = strlen($str);
    $start_byte = 0;
    $end_position = strlen($str);
    $count = 0;
    for($i = 0; $i < strlen($str); $i++){
        if($count >= $position && $start_position > $i){
            $start_position = $i;
            $start_byte = $count;
        }
        if(($count-$start_byte)>=$length) {
            $end_position = $i;
            break;
        }   
        $value = ord($str[$i]);
        if($value > 127){
            $count++;
            if($value >= 192 && $value <= 223) $i++;