从字节数组转换为字符串时的结果奇怪

Question

I get strange results when converting byte array to string and then converting the string back to byte array.

Try this:

     byte[] b = new byte[1];
    b[0] = 172;
    string s = Encoding.ASCII.GetString(b);

    byte[] b2 = Encoding.ASCII.GetBytes(s);
    MessageBox.Show(b2[0].ToString());

And the result for me is not 172 as I'd expect but... 63.

Why does it happen?

Answer 1

Why does it happen?

Because ASCII only contains values up to 127.

When faced with binary data which is invalid for the given encoding, Encoding.GetString can provide a replacement character, or throw an exception. Here, it's using a replacement character of ? .

It's not clear exactly what you're trying to achieve, but:

• If you're converting arbitrary binary data to text, use Convert.ToBase64String instead; do not try to use an encoding, as you're not really representing text. You can use Convert.FromBase64String to then decode.
• Encoding.ASCII is usually a bad choice, and certainly binary data including a byte of 172 is not ASCII text
• You need to work out which encoding you're actually using. Personally I dislike using Encoding.Default unless you really know the data is in the default encoding for the platform you're working on. If you get the choice, using UTF-8 is a good one.

Answer 2

ASCII encoding is a 7-bit encoding. If you take a look into generated string it contains "?" - unrecognized character. You might choose Encoding.Default instead.

Answer 3

ASCII is a seven bit character encoding, so 172 falls out of that range, so when converting to a string, it converts to "?" which is used for characters that cannot be represented.