Why is string.contains() returning false?

Question

I have the following string: \\\?\hid#vid_04d8pid_003f#62edf110800000#{4d1e55b2-f16f-11cf-88cb-001111000030} stored in a string variable (from a function call) called devPathName

and the following defined: const string myDevice = @"vid_04d8pid_003f";

but the following code always evaluates to false:

Boolean test = true;

test = devPathName.Contains(myDevice);

statusLabel.Text += "\n\tThe value of test: " + test.ToString();

It returns true on my machine. You might want to provide more info about the context of that code and how you're testing. — Mehrdad Afshari
– Mehrdad Afshari, Commented Jun 29, 2009 at 3:25

devuxer · Accepted Answer · 2009-06-29 03:07:19Z

7

When I stick your code into C#, the compiler doesn't like the "\h" part of your long string. It says, "unrecognized escape sequence". Could that be your problem?

Oh, and if I put a "@" before the long string, the contains() method returns true.

HTH,

-Dan

answered Jun 29, 2009 at 3:07

devuxer

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Bevan · Accepted Answer · 2009-06-29 04:33:38Z

2

Assuming that you've already checked for letter "O" vs digit "0" and similar things, I'd suggest that the string you're seeing in the string variable devPathName is being encoded for display and isn't quite what you think it is.

For example, if the string contains the character \x000d (Control-M), the Visual Studio debugger will display this as \r when you inspect the value of the string.

Or, for another example, if the string contains the sequence 3504 (three-five-zero-four) but you instead search for 35O4 (three-five-oh-four) then you'll not find a match.

(Depending on your font, you may not be able to see differences between some characters. Compare "0O1lB8S5" with "0O1lB8S5" in different fonts to see what I mean.)

edited Jun 29, 2009 at 4:33

answered Jun 29, 2009 at 3:08

Bevan

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6 Comments

Dark Star1 Over a year ago

Hhmmm.... do you mean I need to convert it using UnicodeEncoding? I actually retrieve that string from an IntPtr ( devPathName = Marshal.PtrToStringAuto(pdevPathName);) but could you please explain what you mean? Thanks

Bevan Over a year ago

@dark-star1 - updated my answer with a clarification, hope this is clearer.

Dark Star1 Over a year ago

You and Pat seem to have hit the nail on the head. attempting to use the Path.* threw up exceptions showing that there's a '\r' and '\n' in there somewhere. I'm guessing this is at the beginning of the returned string. Is there a way to side step this or do I have to copy the string, modify and then test it for my substring?

Bevan Over a year ago

One good rule of thumb is to always sanity check input that comes from outside your application, whether directly entered by a user or not. As a first step, you could use Trim() to remove leading and training whitespace - but if it was my code, I'd go further to be rigourous.

Dark Star1 Over a year ago

You'll have to forgive my sloppiness. I'm learning C# and Visual studio 2008 express environment at the same time. I've always avoided coding on windows for a good reason. Anyways I found out that the string is constructed thus: an '&' is used to aggregate each piece of informationin the string. though this character is not displayed. it was this little thing that was throwing me off.

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SwDevMan81 · Accepted Answer · 2009-06-29 03:21:21Z

0

This returns true for me as well.


using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

namespace WindowsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            const string myDevice = @"vid_04d8pid_003f";
            string devPathName = @"\\\?\hid#vid_04d8pid_003f#62edf110800000#{4d1e55b2-f16f-11cf-88cb-001111000030}";
            Boolean test =devPathName.Contains(myDevice);
            MessageBox.Show("\n\tThe value of test: " + test.ToString());
        }
    }
}

I guess I would put a breakpoint in and make sure that devPathName isnt being changed on you and that the value is what you expect.

answered Jun 29, 2009 at 3:21

SwDevMan81

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4 Comments

Dark Star1 Over a year ago

devPathName is returned thus: devPathName = Marshal.PtrToStringAuto(pdevPathName); and pdevPathName: pdevPathName = new IntPtr(deviceDetailDataBuffer.ToInt32() + 4); I have tried all the following: 1) Path.GetFullPath() => returns and exception saying there're control characters (\r\n), but removing the first 4 characters get's rid of this problem. 2) removing the 1st 8 characters such that the string starts with my required substring. Still returns false.

SwDevMan81 Over a year ago

What type is deviceDetailDataBuffer? Is it a decimal? Where does the value come from? You could create a function to check for only letters/digits and punctuation to remove any escape charactors. See Char.IsLetterOrDigit and Char.IsPunctuation.

Dark Star1 Over a year ago

deviceDetailDataBuffer is an IntPtr that is returned by a function, and the built in string.Replace() functions can apparently remove escape characters.

SwDevMan81 Over a year ago

You might want to try string path_name = Marshal.PtrToStringAuto(deviceDetailDataBuffer);

Windows programmer · Accepted Answer · 2009-06-29 03:41:12Z

0

What's evaluating to false, your test variable or part of the display in statusLabel.text? Are you sure the display isn't something like this:

The value of test: false
The value of test: false
The value of test: false
The value of test: false
The value of test: true
The value of test: false

and maybe you're only looking at the first line of that string?

answered Jun 29, 2009 at 3:41

Windows programmer

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Comments

Pat Hermens · Accepted Answer · 2010-12-19 21:55:10Z

0

You just need to escape the long string before parsing it via .Contains()

Put an at-symbol (@) at the start of the string, as demonstrated in several of the previous answers and it should evaluate perfectly.

When stepping into .Contains, the initial string, in your case

\\\?\hid#vid_04d8pid_003f#62edf110800000#{4d1e55b2-f16f-11cf-88cb-001111000030}"

contains non-escaped characters and causes .Contains to terminate before it completes the comparison.

edited Dec 19, 2010 at 21:55

answered Jun 29, 2009 at 4:00

Pat Hermens

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4 Comments

Dark Star1 Over a year ago

unfortunately there's no way I can escape it that I know of as this string is supposed to be the path to a device returned from a setupapi* function. Do you know of a way/function that would llow me to filter out control characters such as '\r' and '\n'?

Pat Hermens Over a year ago

I think your only option in that case is to save it as a local variable and do whatever you need to before you pass it to .Contains If the function you're passing it to doesn't have the ability to return it as a "safe" string.

Dark Star1 Over a year ago

I finally figured it out. I ws watching the debugger when I noticed that the returned string that describes the device had a '&' between each part was decribing the device. So although the string being displayed is: \\\?\hid#vid_04d8pid_003f#62edf110800000#{4d1e55b2-f16f-11cf-88cb-001111000030}. The actual string in the buffer is: \\\?\hid#vid_04d8&pid_003f#6&2edf1108&0&0000#{4d1e55b2-f16f-11cf-88cb-001111000030}

Pat Hermens Over a year ago

Bevan picked that one. // Credit where credit is due. ;-) Glad you found it and it's working for you.

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