String to byte array only converts first 16 bytes according to Intellisense

Question

I'm trying to convert a string to a byte[] using the ASCIIEncoder object in the .NET library. The string will never contain non-ASCII characters, but it will usually have a length greater than 16. My code looks like the following:

public static byte[] Encode(string packet)
{
    ASCIIEncoder enc = new ASCIIEncoder();
    byte[] byteArray = enc.GetBytes(packet);
    return byteArray;
}

By the end of the method, the byte array should be full of packet.Length number of bytes, but Intellisense tells me that all bytes after byteArray[15] are literally questions marks that cannot be observed. I used Wireshark to view byteArray after I sent it and it was received on the other side fine, but the end device did not follow the instructions encoded in byteArray. I'm wondering if this has anything to do with Intellisense not being able to display all elements in byteArray, or if my packet is completely wrong.

Answer 1

If your packet string basically contains characters in the range 0-255, then ASCIIEncoding is not what you should be using. ASCII only defines character codes 0-127; anything in the range 128-255 will get turned into question marks (as you have observed) because there characters are not defined in ASCII.

Consider using a method like this to convert the string to a byte array. (This assumes that the ordinal value of each character is in the range 0-255 and that the ordinal value is what you want.)

public static byte[] ToOrdinalByteArray(this string str)
{
    if (str == null) { throw new ArgumentNullException("str"); }

    var bytes = new byte[str.Length];
    for (int i = 0; i < str.Length; ++i) {
        // Wrapping the cast in checked() will trigger an OverflowException
        // if the character being converted is out of range for a byte.
        bytes[i] = checked((byte)str[i]);
    }

    return bytes;
}

The Encoding class hierarchy is specifically designed for handling text. What you have here doesn't seem to be text, so you should avoid using these classes.