Absurd error GetInvalidPathChars - System.InvalidCastException

Question

Absurd error GetInvalidPathChars - System.InvalidCastException

DJG 26

Hi,
executing this code i get this error

Dim dir = "C:\Pippo\conversations\conversation\"
Dim CheckDir As Char = System.IO.Path.GetInvalidPathChars(dir)
Dim data() As Byte = File.ReadAllBytes("C:\Ferie\2020_0908_155849_185.jpg")
File.WriteAllBytes(dir & "2020_0908_155849_185A.jpg", data)

System.InvalidCastException
HResult=0x80004002
Messaggio=Cast not valid from string "C:\Pippo\conversations\conversat" to 'Integer' type.
Origine=Microsoft.VisualBasic
Stack analysis:
in Microsoft.VisualBasic.CompilerServices.Conversions.ToInteger(String Value)
in ProvaPath.Form1.Button1_Click(Object sender, EventArgs e) in C:\Progetti\ProvaPath\ProvaPath\Form1.vb: riga 9
in System.Windows.Forms.Control.OnClick(EventArgs e)
in System.Windows.Forms.Button.OnClick(EventArgs e)
in System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
in System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
in System.Windows.Forms.Control.WndProc(Message& m)
in System.Windows.Forms.ButtonBase.WndProc(Message& m)
in System.Windows.Forms.Button.WndProc(Message& m)
in System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
in System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
in System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
in System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
in System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
in System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
in System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
in Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.OnRun()
in Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.DoApplicationModel()
in Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.Run(String[] commandLine)
in ProvaPath.My.MyApplication.Main(String[] Args) in : riga 83

This exception was originally thrown in the following call stack:
Microsoft.VisualBasic.CompilerServices.Conversions.ParseDouble(string, System.Globalization.NumberFormatInfo)
Microsoft.VisualBasic.CompilerServices.Conversions.ToInteger(string)

Eccezione interna 1:
FormatException: Incorrect input string format.

How is it possible?

Thanks.

4 answers

Your answer

Answer 1

DJG 26

Hi cooldadtx,
perhaps i've found the problem, executing your last suggested test, here below the bytes resulting from filename = "0_D_1_6.att", see the last one...

	(0)	48	Byte  
	(1)	95	Byte  
	(2)	68	Byte  
	(3)	95	Byte  
	(4)	49	Byte  
	(5)	95	Byte  
	(6)	54	Byte  
	(7)	46	Byte  
	(8)	97	Byte  
	(9)	116	Byte  
	(10)	116	Byte  
	(11)	0	Byte

Thanks

Michael Taylor 60,326 Reputation points

2022-12-26T17:00:30.437+00:00

That seems to indicate that your FileName has an extra null on the end. You never told us where the value for that variable is coming from but it appears you have bad code setting the value (or the data source it comes from is bad). You don't normally see this unless you're interacting with C/C++ code.

Nevertheless clean up the file (assuming it is just zeroes) using this: FileName = FileName.Replace(vbNullChar, "") and see if the problem goes away.
DJG 26 Reputation points

2022-12-28T16:38:16.443+00:00

Many thanks cooldadtx,
i found different length between client and server conversion strings from Encoding.UTF8.GetBytes, which result in adding the server side null character.
The lenght of the client string is 297 char, instead the resulting bytes conversion with Encoding.UTF8.GetBytes is 302.
I think i'm going to try different code (for example Encoding.GetEncoding(1252).GetBytes)
If none of this tries will be succesfull, i finally will adopt the replace of the vbNullChar like you've suggest me

Thank again for you great help

Best regards

Answer 2

GetInvalidPathChars returns an array of characters that are considered invalid as part of a file path. As such the method has no parameters and returns an array. You are passing an argument to the method and taking the return value and storing it into a single char.

So the question becomes why VB is allowing you to pass an argument to a method that has none. This is a backwards compatibility thing. In VB (prior to .NET) you called subroutines without parens. So GetInvalidPathChars(dir) would have been GetInvalidPathChars dir. For whatever reason the compiler rewrites the code to the invalid, but equivalent, GetInvalidPathChars()(dir). Since the method is returning a character array it tries to index into the array to get the value but it is using a string and not an int and therefore you get the runtime error.

Answer 3

DJG 26

Hi cooldadtx,
thank for the answer.
Now i've tried to remove the As Char from Dim CheckDir As Char = System.IO.Path.GetInvalidPathChars(dir)
and so now i've Dim CheckDir = System.IO.Path.GetInvalidPathChars(dir).
Executing the code now i obtain

'Invalid cast from string "C:\Pippo\conversations\conversat" to type 'Integer'.'

and before this i've received on time chrW(15) not valid (where is chrW(15) in this string ?)

I'm a bit confused

Michael Taylor 60,326 Reputation points

2022-12-24T16:39:23.457+00:00
No, you do not pass data to the GetInvalidPathChars function. That is what I described in my answer. You are trying to dereference the returned character array using a string because that function doesn't take any parameters.

Dim CheckDir = System.IO.Path.GetInvalidPathChars()

There is no function on Path that takes a path and determines if it contains invalid characters or not. You have to write your own function that calls GetInvalidPathChars and then searching the desired path for any of those characters. Here's a Stack Overflow post where several people gave approaches to solving this problem.

Note however that this doesn't mean the path is actually valid or even exists. It just determines if the path contains any characters that are considered invalid. If you need to determine if a path exists then use the Exist method. If you want to determine whether a path is actually formatted properly then the post I linked to has some options but ultimately you don't know until you actually try to use it because file systems ultimately enforce the rules. For example you might have a path with a 1000 character directory name that might work with NTFS but not FAT16 file systems.
DJG 26 Reputation points

2022-12-24T18:23:56.027+00:00

Ok, i've understand, but when i add the directory between the brackets, VS doesn't show me any error, it's really strange.
But the same thing happens for this comand File.WriteAllBytes(dir) is it possible?

Many thanks again
Michael Taylor 60,326 Reputation points

2022-12-24T19:09:34.727+00:00

Can you show the code? If you're literally just calling File.WriteAllBytes(dir) then you have the inverse problem. WriteAllBytes requires the string to write to and the byte array to write. If you're not passing both then that is an issue. But that shouldn't compile either.

As for the directory between brackets, I don't understand. But to catch the error at compile time, instead of waiting until late binding then you need to turn on Strict. It sounds like it is off in your build settings. Go to the project's compile settings. Then find Option Strict and set it on. Now the compiler is going to behave like a more strongly typed language you and fail to compile the original code you posted.

Answer 4

DJG 26

Here is the code.

caratteri non validi nel percorso = invalid characters in the path

Michael Taylor 60,326 Reputation points

2022-12-25T01:32:12.87+00:00
Just at a cursory glance there doesn't appear to be an invalid character in the path but if one the shown characters displays as a valid character but actually isn't then it would be hard to detect in a screenshot. Please show us the call stack associated with the exception along with the parameter name it associates with the error. I'm assuming the folder is actually being created correctly yes?

Note that you should be very careful about manually combining paths together. This can break if a path accidentally ends with a slash. Consider using Path.Combine instead. For example I can rewrite your code as follows.

Dim UserPath As String = Path.Combine(ApplicationPath, $"conversations\conversation_{id_conversation}", $"user_{id_user}") If Not Directory.Exists(UserPath) Then Directory.CreateDirectory(UserPath) End If Dim PathConversation As String = Path.Combine(UserPath, FileName) File.WriteAllBytes(PathConversation, img)

I'm using string interpolation here to reduce the string concatenation calls.
DJG 26 Reputation points

2022-12-25T18:27:24.71+00:00

HI cooldadtx,
i've discovered one more thing.
Now i've change my code folowing your suggestion, that is :

Dim UserPath As String = Path.Combine(ApplicationPath, "conversations", String.Format("conversation_{0}", id_conversation), String.Format("user_{0}", id_user))
If Not Directory.Exists(UserPath) Then
Directory.CreateDirectory(UserPath)
End If

But i still take "invalid characters" error on this comand:

Dim PathConversation As String = Path.Combine(UserPath, Path.GetFileName(FileName))

The FileName is equal to "0_D_6.att"

If i change temporarely at least one character in the Filename the comand doesn't give me any error and also if, after this change i change again the Filename to its original name.

it sounds very strange

Thanks.
Jack J Jun 25,296 Reputation points

2022-12-26T02:29:24.563+00:00

@DJG , based on my test, the code works for me. what is your string of your UserPath?
You could check the following picture where it is different from you.
Michael Taylor 60,326 Reputation points

2022-12-26T04:20:19.32+00:00
That is weird because the characters are valid. But maybe one of the characters in that string are actually not valid. We would be hard pressed to figure that out from here. Can you run that string through this code and show us the results of the encoded?

Dim encoded As Byte() = System.Text.Encoding.ASCII.GetBytes(FileName)

The expected value is 48, 95, 68, 95, 49, 95, 54, 46, 97, 116, 116.
DJG 26 Reputation points

2022-12-26T09:42:13.837+00:00

Hi JackJJun-MSFT,
i think that the problem is in the filename, see my last answer to cooldadtx

Thanks

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Absurd error GetInvalidPathChars - System.InvalidCastException

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