error in simple regex validation

Question

4.50/5 (2 votes)

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i have a textbox which is determining the time, on the form load i have written the code so that the time will be filled in the textbox which is in this format
09:09 AM
i am using the regex for validation purpose
so i have wirtten this code

C#

private bool time()
        {
            Regex regex = new Regex("^(1[0-2]|0[1-9]):[0-5][0-9]\040(AM|am|PM|pm)$");
            if (regex.IsMatch(textBox2.Text))
            {
                return true;
            }
            else
            {
                return false;
            }

       
       
        }

there is a button in the form which is for showing if the error is there then the error provider shows the error, and if not, then error provider doesnt blink, the code for button click is

the problem is when i keep the textbox blank and clicks the button, the error provider doesnt shows the error
even if i put ''09:09 st'' instead of ''09:09 pm'' it doesnt shows error

Posted 26-Dec-12 2:13am

sariqkhan

Updated 26-Dec-12 7:38am

v3

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Comments

Suvabrata Roy 26-Dec-12 8:41am

Regex regex = new Regex("^(1[0-2]|0[1-9]):[0-5][0-9]\040(AM|PM|)$",System.Text.RegularExpressions.RegexOptions.IgnoreCase);

sariqkhan 26-Dec-12 9:07am

even if i put 09:09 st instead of 09:09 am it works and there is no error provide which blinks

Sergey Alexandrovich Kryukov 26-Dec-12 16:59pm

I don't observe it. It shows the error even if this is "09:09 AM". Why \040? Why 1 and 2? The general idea is correct should work. Refine the detail.
And describe what exactly should match and what not. Do you mean it should be "hh:mm (AP|PM)" format? And remove different cases, just make the search not case-sensitive.
—SA

2 solutions

Solution 1

Hi!,
Try to test for text blank first,in the time(), like this

C#

private bool time()
        {
            Regex regex = new Regex("^(1[0-2]|0[1-9]):[0-5][0-9]\040(AM|am|PM|pm)$");
            //Tests for Null, Empty or just white space.
            if (string.IsNullOrWhiteSpace(textBox2.Text))
            {
                return false;
            }
            if (regex.IsMatch(textBox2.Text))
            {
                return true;
            }
            else
            {
                return false;
            }
 
        }

Posted 26-Dec-12 2:21am

Guilherme Morais

Comments

sariqkhan 26-Dec-12 8:44am

sir your code is correct but the the problem is when i put
09:09 st instead of 09:09 PM it does not shows error

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Sergey Alexandrovich Kryukov · Accepted Answer · 2012-12-26T11:08:00

Please see my comment to the question. I found a bug: you forgot to escape ':'. Make it '\:', escaped.

Besides, I would greatly simplified it, employing additional validation via C# after Regex validation. Do this:

Use the pattern ^([0-9][0-9])\:([0-9][0-9]) (AM|PM)$, and make the case-insensitive match.

It will give you three string string groups, inside round brackets. Extract two groups with digits and test each for comparison with numbers:

C#

string digitGroupText = //... take from Regex
// it will be anything from 00 to 99, but only 00 to 59 is valid...

byte number = byte.Parse(digitGroupText); // as Regex validation is passed, this should always be successful

if (number > 59) //... then it is invalid

Got the idea? Regex along is not suitable for each and every validation.

Good luck,

—SA