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I am looking for a Regular expression to match only if a date is in the first 28 days of the month. This is for my validator control in ASP.NET
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Here are the details: The regex will match a string only if it contains at least one valid date, like: [dd-mm] Assuming the year in question is not a leap year. The number of days each month should have are: January 31 days February 28 days So on All text outside a valid date can be ignored, including other invalid dates.
A regular expression for dates (YYYY-MM-DD) should check for 4 digits at the front of the expression, followed by a hyphen, then a two-digit month between 01 and 12, followed by another hyphen, and finally a two-digit day between 01 and 31. Here’s the regex code that does all this: /^d{4}-(0[1-9]|1[0-2])-(0[1-9]|[12][0-9]|3[01])$/
The month is matched by 0[1-9]|1[012], again enclosed by parentheses to keep the two options together. By using character classes, the first option matches a number between 01 and 09, and the second matches 10, 11 or 12. The last part of the regex consists of three options.
Regular Expression for YYYY-MM-DD Dates A date should start with a 4 digit year from 0000-9999. We can specify this using the following: /d {4}/
Don't do this with Regex. Dates are formatted differently in different countries. Use the DateTime.TryParse routine instead:
DateTime parsedDate;
if ( DateTime.TryParse( dateString, out parsedDate) && parsedDate.Day <= 28 )
{
// logic goes here.
}
Regex is nearly the golden hammer of input validation, but in this instance, it's the wrong choice.
164
I don't think this is a task very well-suited for a regexp.
I'd try and use the library functions (DateTime.Parse for .NET) to parse the date and then check the day component of it. Everything else is duplicating half the library function anyways.
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