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...

In my last article on Regular Expressions, we looked at a couple of simple expressions and 3 algorithms to use the expressions for “validating” strings. The main point of the article is that Regular Expression behavior will be confusing if not considered in the context of the algorithm being used. Please take a look at Regular Expressions. What’s that got to do with C#? to get the background for this article. In this article, we will discuss one of the more difficult Regular Expression problems. How do you use “Negative Look-ahead” ? To use Regular Expression “Negative Look-Ahead” or “Negative Look-Behind”, you have to change the way you think about pattern matching. First, the negative look-ahead takes the syntax… “(?!pattern)” In the words of the MSDN documentation… (Zero-width negative lookahead assertion.) Continues match only if the subexpression does not match at this position on the right. For example, \b(?!un)\w+\b matches words that do not begin with un. This expres...