Yet Another C# Blog

In my last article titled "Regular Expression Alternation" we discussed Alternation as one means of performing the AND operation in a regular expression pattern. (?(expression)yes|no) But, what if you don't have this pattern in your version of RegEx? Some of you may be reading to gain knowledge that you can apply in other programming languages besides C# or the .NET environment. The pattern I described in the last article does not work in all versions of .NET Regular Expressions. In particular, it does not work in JScript Regular Expression Syntax. And, when you use tools like ASP.NET’s RegularExpressionValidator, you are implicitly using JScript. So then, what do you do? To restate the original requirement, we want to validate a string that has at least one digit, at least one uppercase letter, and at least 6 characters. The problem statement is clearly an AND problem, so it begs to be written with the Alternation pattern. But in situations where we can...

I promised in my last article that I'd have more to say about regular expression. So here you have it. Today, we look at another tough problem for Regular Expressions. Let’s consider writing a pattern to validate that a string contains at least one digit, at least one uppercase letter, and at least 6 characters. One would think that this would be easy. But here we’re faced with an AND situation and the regular expression syntax doesn't provide an AND operator. Take, for example, any validation problem that has the form… A and B and C Without an AND operation in Regex, you are almost forced to go outside of the pattern and implement the test in multiple patterns and multiple passes of your validator. That may be the best approach, or it may be impossible if you are working with a blackbox validator and must provide a single Regex pattern. I've found two approaches that can be applied to solve such problems. We'll discuss one of those approaches today. The app...