中英文截取长度

    #region 中英文截取长度一致
    //是否是中文
    public static bool IsChinese(char c)
    {
        return (int)c >= 0x4E00 && (int)c <= 0x9FA5;
    }

    //获得字节长度
    private static int getLengthb(string str)
    {
        return System.Text.Encoding.Default.GetByteCount(str);
    }

    //c#的中英文混合字符串截取指定长度,startidx从0开始 by gisoracle@126.com
    public static string getStrLen(string str, int startidx, int len)
    {
        int Lengthb = getLengthb(str);
        if (startidx + 1 > Lengthb)
        {
            return "";
        }
        int j = 0;
        int l = 0;
        int strw = 0;//字符的宽度
        bool b = false;
        string rstr = "";
        for (int i = 0; i < str.Length; i++)
        {
            char c = str[i];
            if (j >= startidx)
            {
                rstr = rstr + c;
                b = true;
            }
            if (IsChinese(c))
            {
                strw = 2;
            }
            else
            {
                strw = 1;
            }
            j = j + strw;
            if (b)
            {
                l = l + strw;
                if ((l + 1) >= len) break;

            }
        }
        return rstr;
    }
    #endregion