VB.NET encoding one character wrong

Question

I have a byte array that I'm encoding to a string:

Private Function GetKey() As String
    Dim ba() As Byte = {&H47, &H43, &H44, &H53, &H79, &H73, &H74, &H65, &H6D, _
                        &H73, &H89, &HA, &H1, &H32, &H31, &H36}

    Dim strReturn As String = Encoding.ASCII.GetString(ba)

    Return strReturn
End Function

Then I write that to a file via IO.File.AppendAllText. If I open that file in 010 Editor (to view the binary data) it displays as this:

47 43 44 53 79 73 74 65 6D 73 3F 0A 01 32 31 36

The original byte array contained 89 at position 11, and the encoded string contains 3F. If I change my encoding to Encoding.Default.GetString, it gives me:

47 43 44 53 79 73 74 65 6D 73 E2 80 B0 0A 01 32 31 36

Any help would be much appreciated!

Answer 1

Encoding.ASCII is limited to 7-bit characters. That is byte values from 0 to 127 (&H00 to &H7F). GetString sets all values outside this range to &H3F which is a questionmark.

Encoding.Default is the current ANSI code page for the operating system which on my computer is CodePage 1252..

The ANSI code pages can be different on different computers, or can be changed for a single computer, leading to data corruption. For the most consistent results, applications should use Unicode, such as UTF-8 (code page 65001) or UTF-16, instead of a specific code page.

Encoding.UTF7 would work for you here:

Dim strReturn As String = Encoding.UTF7.GetString(ba)

Edit:

Instead of using Encoding I'd write the bytes directly using something like this:

Dim key = GetKey()
Dim f = System.IO.File.OpenWrite("output.txt")
f.Seek(0, SeekOrigin.End)
f.Write(key, 0, key.Length)
f.Close()

Private Function GetKey() As String
  Dim ba() As Byte = {&H47, &H43, &H44, &H53, &H79, &H73, &H74, &H65, &H6D, &H73, &H89, &HA, &H1, &H32, &H31, &H36}

  Return ba
End Function