php截取utf8或gbk编码中英文字符串

//字符串截取
$a = "s＠@你好";
var_dump(strlen_weibo($a,'utf-8'));
结果输出为8，其中字母s计数为1，全角＠计数为2，半角@计数为1，两个中文计数为4。源码如下：
//截取字符串的函数代码
function strlen_weibo($string, $charset='utf-8')
{
    $n = $count = 0;
    $length = strlen($string);
    if (strtolower($charset) == 'utf-8')
    {
        while ($n         {
            $currentByte = ord($string[$n]);
            if ($currentByte == 9 ||
                $currentByte == 10 ||
                (32             {
                $n++;
                $count++;
            } elseif (194             {
                $n += 2;
                $count += 2;
            } elseif (224             {
                $n += 3;
                $count += 2;
            } elseif (240             {
                $n += 4;
                $count += 2;
            } elseif (248             {
                $n += 5;
                $count += 2;
            } elseif ($currentByte == 252 || $currentByte == 253)
            {
                $n += 6;
                $count += 2;
            } else
            {
                $n++;
                $count++;
            }
            if ($count >= $length)
            {
                break;
            }
        }
        return $count;
    } else
    {
        for ($i = 0; $i         {
            if (ord($string[$i]) > 127)
            {
                $i++;
                $count++;
            }
            $count++;
        }
        return $count;
    }
}