here is a sketch of the code that caused that issue:
at the class level these variables are defined:
Private
Const STATE_LENGTH_M1 As Integer = 256 - 1Private _state(STATE_LENGTH_M1) As Byte
within an instance method, something like the following was the cause of the problem (simplified -- the debugger still loses the values in this simple case, btw):
Dim
n As Byte = 0'....
n = _state(i) + _state(j)
Although the fix to this code was pretty trivial, when the IDE broke on this line, the values contained in array _state were "undefined" which made it tough to identify the cause (since the line was more complicated)
Here was the fix:
Dim n As Integer = 0
n = (CType(_state(i), Integer) + CType(_state(j), Integer)) Mod 256
'use the value of n in a subsequent expression as Convert.ToByte(n) Since the IDE had "lost" the values, this simple bug took much longer to fix than it should have...
BUG: debugger losing variable values
suparba
Question 2) The message is generated at run time to replace the typename with the actual type (in this case Byte):
I searched the integrated help for "Constant expression not representable in type" and the first topic was the one you probably are looking for:
Constant expression not representable in type '<typename>'
Question 1) You are right, F1 on the watch window bring up general help about the watch window, that I think is the expected behavior (help on individual exceptions is available using the exception assistant)
Question 3) Yes, it is true, sometimes the error message from the watch window is different than the one in code, but in this scenario I think it is a pretty good error message (especially since I can see the value of _state(i) and _state(j))
Still, too bad I could not reproduce the scenario you run into where the values were not displayed.
Yury_A
the specific watch window message does beg three questions, however. 1) "Why aren't these messages searchable in the integrated help from the watch window " 2) "Why aren't these messages in the integrated help " and 3) "Why doesn't the watch window throw the same error that the code does ". First, Selecting the message in the watch window and pressing F1 results in general help about the watch window. Next, Pasting the message into the search page yields no topically applicable results. Finally, that the watch window and the code line yield different results suggests that the code and the watch window are not 100% in sync.
tbrierly
I’m sorry to hear that this had you hung up for so long! I just tried this out on the final version of VS2005 – what I get is the exception dialog stating that there was an overflow exception, and when I examine the watch window at that point (or hover over the variables) I’m seeing the correct values in the byte array, so it looks like this is something that got addressed between releasing beta2 and the final product. If & when you upgrade to the final version, I’d really like to hear if this problem has indeed gone away for you – please let us know!
--Matt--*
VirginiaA
Thanks for the response.
My December partner bundle just arrived and I plan to migrate over the weekend. I will test this scenario out and see if it is still an issue.
Matt Waldron
Thanks for reporting this issue but I am not sure how to repro it: I run the following code and the debugger will stop at the exception but the values in the array are not "undefined".
Module1Module
Sub Main()
Dim i As New c
i.OverFlow()
End Sub
Class c
Private Const STATE_LENGTH_M1 As Integer = 256 - 1
Private _state(STATE_LENGTH_M1) As Byte
Sub OverFlow()
Dim n As Byte = 0
_state(1) = 200
_state(2) = 200
n = _state(1) + _state(2)
End Sub
End Class
End Module
If you have time to post the simplified code that caused the problem I could look into it.
Luca
VB Test Team
RichardGreenwell
it was a short piece based upon the "CipherSaber" algorithm -- since the code for the whole class is short, I'll post it up -- the problem has been fixed in the class listing below
Dim n As Integer = 0
'...
n = (CType(_state(i), Integer) + CType(_state(j), Integer)) Mod 256
which would have been
Dim n As Byte = 0
n = _state(i) + _state(j)
as a note, I was also unable to duplicate the problem on my machine at work (Server 2003, VS Beta 2) -- my home machine is XP Pro SP2, VS Beta 2 -- doubt the OS makes a difference, but it might...
class listing
Imports System.Security
Imports System.Security.Cryptography
Public Interface ICipherSabre
Property Key() As String
''' <summary>
''' Encrypts a String
''' </summary>
Function Encrypt(ByVal PlainText As String) As Byte()
''' <summary>
''' Decrypts a String
''' </summary>
Function Decrypt(ByVal CipherBytes() As Byte) As String
End Interface
Public Class CipherSabre
Implements ICipherSabre
Private Const IV_LENGTH_M1 As Integer = 10 - 1
Private Const KEY_LENGTH_MAXIMUM_M1 As Integer = 256 - 1
Private Const STATE_LENGTH_M1 As Integer = 256 - 1
Private _iv(IV_LENGTH_M1) As Byte
Private _key(KEY_LENGTH_MAXIMUM_M1) As Byte
Private _state(STATE_LENGTH_M1) As Byte
Public Sub New(ByVal Key As String)
'initialize IV
Dim gen As New RNGCryptoServiceProvider()
gen.GetBytes(_iv)
Me.Key = Key
__SetStateArray()
End Sub
Public Sub New(ByVal Key As String, ByVal IV() As Byte)
If (IV.Length = IV_LENGTH_M1 + 1) Then
IV.CopyTo(_iv, 0)
Else
Exit Sub
End If
Me.Key = Key
__SetStateArray()
End Sub
Public Function Decrypt(ByVal CipherBytes() As Byte) As String Implements ICipherSabre.Decrypt
For nloop As Integer = 0 To IV_LENGTH_M1
_iv(nloop) = CipherBytes(nloop)
Next
'initialize loop variables
Dim i As Integer = 0
Dim j As Integer = 0
Dim n As Integer = 0
'length of output string
Dim nlength As Integer = CipherBytes.Length - IV_LENGTH_M1 - 1
'input/output characters
Dim CharOut(nlength) As Char
'swap byte
Dim byt As Byte
'loop the byte array
For nloop As Integer = 0 To nlength - 1
Debug.WriteLine("iteration " & nloop.ToString())
i = (i + 1) Mod (STATE_LENGTH_M1 + 1)
j = (j + _state(i)) Mod (STATE_LENGTH_M1 + 1)
byt = _state(i)
_state(i) = _state(j)
_state(j) = byt
n = (CType(_state(i), Integer) + CType(_state(j), Integer)) Mod 256
CharOut(nloop) = Convert.ToChar(CipherBytes(IV_LENGTH_M1 + 1 + nloop) Xor Convert.ToByte(n))
Next
Return (CharOut)
End Function
Public Function Encrypt(ByVal PlainText As String) As Byte() Implements ICipherSabre.Encrypt
'initialize loop variables
Dim i As Integer = 0
Dim j As Integer = 0
Dim n As Integer = 0
'length of input string
Dim nlength As Integer = PlainText.Length
'input/output characters
Dim bytOut(IV_LENGTH_M1 + nlength) As Byte
_iv.CopyTo(bytOut, 0)
'Dim characters() As Char = PlainText.ToCharArray
'swap byte
Dim byt As Byte
'loop the string
For nloop As Integer = 0 To nlength - 1
Debug.WriteLine("iteration " & nloop.ToString())
i = (i + 1) Mod (STATE_LENGTH_M1 + 1)
j = (j + _state(i)) Mod (STATE_LENGTH_M1 + 1)
byt = _state(i)
_state(i) = _state(j)
_state(j) = byt
n = (CType(_state(i), Integer) + CType(_state(j), Integer)) Mod 256
bytOut(IV_LENGTH_M1 + 1 + nloop) = Convert.ToByte(PlainText(nloop)) Xor Convert.ToByte(n)
Next
Return (bytOut)
End Function
Protected Overrides Sub Finalize()
End Sub
Public Property Key() As String Implements ICipherSabre.Key
Get
Return (BitConverter.ToString(_key))
End Get
Set(ByVal value As String)
Dim keylen As Integer = value.Length + IV_LENGTH_M1 + 1
If keylen > 256 Then
Throw New ArgumentOutOfRangeException("Key", "Length of key must be less than 256 ASCII characters")
Exit Property
End If
ReDim _key(keylen - 1)
_iv.CopyTo(_key, 0)
For nloop As Integer = 0 To (value.Length - 1)
_key(IV_LENGTH_M1 + 1 + nloop) = Convert.ToByte(value(nloop))
Next
End Set
End Property
Private Sub __SetStateArray()
'populate state array
For nloop As Integer = 0 To STATE_LENGTH_M1
_state(nloop) = Convert.ToByte(nloop)
Next
'index variables
Dim j As Integer = 0 'following the ciphersaber convention
Dim n As Integer 'following the ciphersaber convention
'repeatedly calculating this in the loop makes no sense
Dim keylength As Integer = _key.Length
'swap variable
Dim byt As Byte
'mix the state array
For i As Integer = 0 To STATE_LENGTH_M1
n = i Mod keylength
j = (j + _state(i) + _key(n)) Mod (STATE_LENGTH_M1 + 1)
byt = _state(i)
_state(i) = _state(j)
_state(j) = byt
Next
End Sub
End Class
GreyW63
I tried on a recent build but I could not repro your problem: the values were displayed as expected and adding _state(i) + _state(j) to the watch window gave me the very useful error: Constant expression not representable in type 'Byte'.
Luca