C# matching regex to HHMMSS

Question

I'm using VS 2010 Data Generator to generate test strings based on a regular expression.

At the moment I'm having difficulty using the appropriate pattern to generateHHMMSS time strings.

So far I have this, but it's not wholly accurate: ([01]?[0-9]|2[0-3])[0-5][0-9][0-5][0-9]

For example one desired set would be like: 212013

Answer 1

The following should meet your format requirements:

([01][0-9]|2[0-3])[0-5][0-9][0-5][0-9]

The section ([01][0-9]|2[0-3]) covers 00 to 23, whilst [0-5][0-9] covers 00 to 59.

In your original, the ? was making the leading zero or one optional, and thus potentially generating invalid five-digit numbers.

Answer 2

If you don't care for regexes, how about this:

var r = new Random();
DateTime.FromOADate(r.NextDouble()).ToString("HHmmss")