Why Regex.Ismatch return fail

Question

I had used Regex string:

versionPattern = @"^\d+(.\d+){3}$"

to check format of string with 4 number have hyphen is .

xxx.xxx.xxx.xxx or x.x.x.x ...

But it return true with string:

1.0.0.123

and return false with string:

1.0.0.4

My code for this:

if (Regex.IsMatch(svnShopLoorTable.Rows[i].ItemArray[2].ToString(), versionPattern))
{
     //MessageBox.Show("OK");
}
else
{
     //MessageBox.Show("Should be: x.x.x.x");
     s += "\r\nProgram " + svnShopLoorTable.Rows[i].ItemArray[1].ToString() + " of SHOPFLOOR has wrong version format: "
                        + svnShopLoorTable.Rows[i].ItemArray[2].ToString() + " should be formated as: " + "x.x.x.x";
    Console.WriteLine(s);
}

When svnShopLoorTable.Rows[i].ItemArray[1].ToString() is 1.0.0.123 it's ok, not display s. But when svnShopLoorTable.Rows[i].ItemArray[1].ToString() is 1.0.0.4, it's display log in console:

Program SetupSheet of SHOPFLOOR has wrong version format: 1.0.0.4 should be formated as: x.x.x.x

I don't know why this problem occur. Please help me to explain and solve this. Appreciate any help!

can't reproduce regex101.com/r/nC0wV7/1 , maybe try adding a m modifer @"(?m)regex" — Avinash Raj
– Avinash Raj, Commented Sep 25, 2015 at 3:04
It returns true for both cases, although I would escape the literal . for both good practice and to make sure it's validating an actual dot (otherwise it means any character - except newline). — hwnd
– hwnd, Commented Sep 25, 2015 at 3:05
If you put a backslash before the dot, then your problem was the dot, meaning any character. You don't want that. It shouldn't fail the regex, though I guess it's possible that the dot would eat digits too early and cause there to be none for the remaining groups. — siride
– siride, Commented Sep 25, 2015 at 3:45
do you have check any blank before or after 1.0.0.4 ,if so ,you can remove ^$ and try — Kerwin
– Kerwin, Commented Sep 25, 2015 at 3:46

Ronald Rogers · Accepted Answer · 2015-09-25 03:45:50Z

1

I'm going to take a wild-guess and assume that you have some white-space before or after invalidating your regex.

Your regular expression is valid when that line contains that and only that pattern.

Make sure you do not have any white-space preceding or following "1.0.0.4", or modify your regex to be less strict:

versionPattern = @"\d+(.\d+){3}"

Or to handle whitespace:

versionPattern = @"^\s*\d+(.\d+){3}\s*$"

Also you should put a backslash ("\") before the dot ("."), as the dot matches any character in regex.

Meaning this:

 ^\d+(.\d+){3}$

Would also match this:

1a2b3c4

But this would not:

^\d+(\.\d+){3}$

It would only work if the intervening characters were actual dots.

Edit: Now that I see your code I realize that you can also probably just get a away with a Trim, assuming I'm not wrong.

svnShopLoorTable.Rows[i].ItemArray[1].ToString().Trim()

edited Sep 25, 2015 at 3:45

answered Sep 25, 2015 at 3:40

Ronald Rogers

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1 Comment

Neo Over a year ago

Thank you so much, bro. You saved my day. Problem is solved!

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