public static string SubString(string demand, int length, string substitute)
{
demand = DataSecurity.HtmlDecode(demand);
if (Encoding.Default.GetBytes(demand).Length <= length)
{
return(demand);
}
ASCIIEncoding encoding = new ASCIIEncoding();
length -= Encoding.Default.GetBytes(substitute).Length;
int num = 0;
StringBuilder builder = new StringBuilder();
byte[] bytes = encoding.GetBytes(demand);
for (int i = 0; i < bytes.Length; i++)
{
if (bytes[i] == 0x3f)
{
num += 2;
}
else
{
num++;
}
if (num > length)
{
break;
}
builder.Append(demand.Substring(i, 1));
}
builder.Append(substitute);
return(builder.ToString());
}
