网页中实现截取等宽长度中英文字符串

/// <summary>
/// 截取指定长度中英文字符串(宽度一样)
/// </summary>
/// <param name="str">要截取的字符串</param>
/// <param name="length">截取长度,中文字符长度</param>
/// <returns>截取后的字符串</returns>
public static string CutStr(string str, int length)
{
    if (str == null)
        return string.Empty;

    int len = length * 2;
    int j = 0, k = 0;
    Encoding encoding = Encoding.GetEncoding("gb2312");

    for (int i = 0; i < str.Length; i++)
    {
        byte[] bytes = encoding.GetBytes(str.Substring(i, 1));
        if (bytes.Length == 2)//不是英文
            j += 2;
        else
            j++;

        if (j <= len)
            k += 1;

        if (j >= len)
            return str.Substring(0, k) + "...";
    }
    return str;
}