Length cannot be less than zero

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Excuse me, I have a program and I got some error. there Is error in "Dim fileoutput As String = TextBox2.Text.Substring(0, TextBox2.Text.Length - 4)" from my program, please help me for my studying. thank you, sorry for my bad English.

What I have tried:

C#

Private Sub namafiledeskrip()
        Dim posisi As Integer = 0
        Dim t As Integer = 0

        While TextBox2.Text.IndexOf("\"c, t) <> -1
            posisi = TextBox2.Text.IndexOf("\"c, t)
            t = posisi + 1
        End While

        Dim fileoutput As String = TextBox2.Text.Substring(0, TextBox2.Text.Length - 4)
        fileoutput = fileoutput.Substring((posisi + 1))
        RichTextBox2.Text = fileoutput.Replace("_"c, "."c)


    End Sub

Posted 26-Nov-16 6:57am

Member 11905957

Updated 26-Nov-16 20:33pm

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Afzaal Ahmad Zeeshan 26-Nov-16 14:54pm

Index must be zero or greater, that is why the problem.

Member 11905957 27-Nov-16 9:23am

Thank You Sir

3 solutions

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OriginalGriff · Accepted Answer · 2016-11-26T07:23:00

Solution 1

The error message is pretty explicit: "Length cannot be less than zero"
Since you are passing the length based on the Textbox content:

VB

Dim fileoutput As String = TextBox2.Text.Substring(0, TextBox2.Text.Length - 4)

The problem is almost certainly that the text box contains three characters or less...

Posted 26-Nov-16 7:23am

OriginalGriff

Comments

Member 11905957 26-Nov-16 12:31pm

yes sir, my text box is contains more 3 characters, so what have I change Sir from my code? thank for helping me Sir..

OriginalGriff 26-Nov-16 12:36pm

How are you sure? What does the debugger say? The error message say it doesn't...
Are you sure you are using the right textbox?

Member 11905957 27-Nov-16 8:41am

oh yeah, thank you, i get it sir, its work, thank you

OriginalGriff 27-Nov-16 8:51am

You're welcome!

Member 11905957 27-Nov-16 9:09am

Sir, can you help me again?

OriginalGriff 27-Nov-16 9:15am

unless it's with the same problem, you should post it as a new question - it makes it easier to find for others with the same problem.

Member 11905957 27-Nov-16 9:21am

hehe it's the different problem Sir , thanks for your suggestion Sir.. nice to learn with you..

OriginalGriff 27-Nov-16 9:25am

No problem!

Member 11905957 21-Feb-17 12:45pm

Hello Sir, I got some error "Object reference not set to an instance object", can You help me Sir?? thank you.

OriginalGriff 21-Feb-17 13:06pm

At the risk of repeating myself:
"unless it's with the same problem, you should post it as a new question - it makes it easier to find for others with the same problem."

But...we can't fix that for you.
This is one of the most common problems we get asked, and it's also the one we are least equipped to answer, but you are most equipped to answer yourself.

Let me just explain what the error means: You have tried to use a variable, property, or a method return value but it contains null - which means that there is no instance of a class in the variable.
It's a bit like a pocket: you have a pocket in your shirt, which you use to hold a pen. If you reach into the pocket and find there isn't a pen there, you can't sign your name on a piece of paper - and you will get very funny looks if you try! The empty pocket is giving you a null value (no pen here!) so you can't do anything that you would normally do once you retrieved your pen. Why is it empty? That's the question - it may be that you forgot to pick up your pen when you left the house this morning, or possibly you left the pen in the pocket of yesterdays shirt when you took it off last night.

We can't tell, because we weren't there, and even more importantly, we can't even see your shirt, much less what is in the pocket!

Back to computers, and you have done the same thing, somehow - and we can't see your code, much less run it and find out what contains null when it shouldn't.
But you can - and Visual Studio will help you here. Run your program in the debugger and when it fails, VS will show you the line it found the problem on. You can then start looking at the various parts of it to see what value is null and start looking back through your code to find out why. So put a breakpoint at the beginning of the method containing the error line, and run your program from the start again. This time, VS will stop before the error, and let you examine what is going on by stepping through the code looking at your values.

But we can't do that - we don't have your code, we don't know how to use it if we did have it, we don't have your data. So try it - and see how much information you can find out!

Member 11905957 21-Feb-17 13:26pm

Sorry for disturbing You Sir, I have wrote question, but I more interesting with your answer Sir. really. I have tried to debug and I put a breakpoint at the error line in my program. and one of the variable say "nothing". is it mean that variable is null?? that variable as byte. Thanks a lot for your respect Sir.

OriginalGriff 21-Feb-17 14:00pm

Normally, yes.
But a byte is a value type, so it can't be null - only reference types can be null.
So have a look at the rest of it, and see if there is anything else in there.

Member 11905957 23-Feb-17 6:32am

yeah I understood about the risk Sir. evidently the variable is crash with the other variable on top. Thanks for your explanation Sir.

Peter Leow · Accepted Answer · 2016-11-26T07:28:00

Based on the error message, apparently your TextBox2.Text.Length is less than 4 which resulted in negative value from their subtraction. You can't have a negative length for the second argument of Substring() method.
Look like you are trying to remove the dot extension from your file path, if so, you should first ascertain that that dot extension exists, e.g.

C#

Dim value As String = "peterleow/haha.html"

If value.LastIndexOf("."c) <> -1 Then
    Console.WriteLine(value.Substring(0, value.LastIndexOf("."c)))
End If

Learn LastIndexOf[^]

Patrice T · Accepted Answer · 2016-11-26T20:33:00

Solution 3

VB

TextBox2.Text.Substring(0, TextBox2.Text.Length - 4)

This extract the contain of TextBox2 minus the last 4 chars, this imply that it will fail if there is not at least 4 chars.
To proof your code, you gave to check if length is more than 4 and tell what to do otherwise.

Posted 26-Nov-16 20:33pm

Patrice T

Comments

Member 11905957 27-Nov-16 8:42am

Thank you Sir

Length cannot be less than zero

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Length cannot be less than zero

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