Regex does not work properly

Question

I have a windows form, in which i have a textbox. I want to check using Regex that the text inserted does not contain any other character except:

Alphabetic letters [a-z] or [A-Z]
Numbers, 0-9
_ (underscore) or . (Dot)

I have written this line of code which seems to not work properly.
In VB.NET/C#:

Regex.IsMatch(txtCreateDomain.ToString(), "^[a-zA-Z0-9_.]*$")

I want for example to create a variable like below:
C#

bool isValid = Regex.IsMatch(txtCreateDomain.ToString(), "^[a-zA-Z0-9_.]*$")

VB

Dim isValid As Boolean = Regex.IsMatch(txtCreateDomain.ToString(), "^[a-zA-Z0-9_.]*$")

What am i missing?

If `txtCreateDomain` is a TextBox you should be calling `txtCreateDomain.Text` and not `ToString()`. — Visual Vincent, May 31 '16 at 13:47

score 2 · Answer 1 · edited May 23 '17 at 12:15

2

Try this:

Regex.IsMatch(txtCreateDomain.ToString(), "^[a-zA-Z0-9_.]*$")

Edit:

Since you're trying to validate domain names a better solution would be to use the solution described here:

// https://stackoverflow.com/a/967610/162671
private static bool IsValidDomainName(string name)
{
    return Uri.CheckHostName(name) != UriHostNameType.Unknown;
}

Or something like this:

var valid = false;
try
{
    var uri = new Uri("http://example.com/");
    valid = false;
}
catch (UriFormatException){
    valid = false;
}

edited May 23 '17 at 12:15

Community

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answered May 31 '16 at 12:51

Nasreddine

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@Nasreddine not if the dot is inside the character class. – Lucas Araujo May 31 '16 at 12:55
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I learned something today. Thanks @user6188402 and lbarros. – Nasreddine May 31 '16 at 12:56
From my Regex i want all this cases to be valid: domain.intern , domain1.intern, my-domain.intern @user6188402 – drgmak May 31 '16 at 12:57
1

@drgmak are you trying to validate domain names? – Nasreddine May 31 '16 at 12:57
@Nasreddine yes, I am. – drgmak May 31 '16 at 12:58
@drgmak A better solution would be something like [this](http://stackoverflow.com/a/967610/162671) instead of a regex – Nasreddine May 31 '16 at 13:04

eol · Accepted Answer · 2016-05-31T14:10:49.027

1

You forgot the underscore and the dash:

bool isValid = Regex.IsMatch(txtCreateDomain.Text, "^[a-zA-Z0-9_.-]*$")

edited May 31 '16 at 14:10

answered May 31 '16 at 12:56

eol

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This will check only if the text contains all of these right? From my Regex i want all this cases to be valid: domain.intern , domain1.intern, my-domain.intern – drgmak May 31 '16 at 13:03
All of these will match, yes. But if you want to validate domain names maybe have a look at: http://stackoverflow.com/questions/24730805/regex-to-match-a-capture-a-domain-name or https://www.safaribooksonline.com/library/view/regular-expressions-cookbook/9781449327453/ch08s15.html – eol May 31 '16 at 13:06
Thanx, this solved my issue. :) – drgmak May 31 '16 at 13:36
`Regex.IsMatch(txtCreateDomain.ToString(), @"^[\w.-]*$", RegexOptions.ECMAScript)` is simpler, I think. In VB.NET, the `@` should be removed of course. Also, there is no dash in the pattern, only a *hyphen*. BTW, there is no requirement to match a hyphen in the question. That looks suspicious. – Wiktor Stribiżew May 31 '16 at 13:39
@WiktorStribiżew Of course `\w` is simpler, I decided to keep it anyway. Thanks for pointing out that it's a hyphen, not a dash, I wasn't aware of that. Regarding matching the hypen: it's not mentioned in the question, but it's mentioned in the comments for my answer and Nasreddine's answer... – eol May 31 '16 at 13:55
1

Good, still, the question should contain all the details required to answer it. I do not find fault with your answer, just the question itself. – Wiktor Stribiżew May 31 '16 at 13:58
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I am sorry for the mistakes in the question. I appreciaty your help. Thanx for your time – drgmak May 31 '16 at 14:46

Om Prakash · Answer 3 · 2016-05-31T13:06:10.183

0

/^\w+$/

\w is equivalent to [A-Za-z0-9_]

edited May 31 '16 at 13:06

answered May 31 '16 at 13:01

Om Prakash

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user6188402 - Thnx for inform me. i am new here so didn't this. – Om Prakash May 31 '16 at 13:08
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`\w is equivalent to [A-Za-z0-9_]` - not in .NET by default. – Wiktor Stribiżew May 31 '16 at 13:13

Regex does not work properly

3 Answers3