Yet Another C# Blog

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...

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...

...Only that I often need to know Regular Expressions for my C# work. However, the online help and resources seem to come up a little short. So, today I diverge a little and discuss this cryptic yet valuable ancillary topic to try to help you through your next Regex dilema. I'm not going to waste time and internet bandwidth explaining what a Regular Expression is , there are plenty of sites for those. But, I will give special thanks here to OmegaMan who compiled and posted the following on the MSDN Regex Forum... OmegaMan's .Net Regex Resources Reference I refer to it often. So let's dive right in. Whenever you are considering using regular expressions, you need to determine what kind of pattern matching problem are you trying to solve. 1) Do I want a regular expression to check a string for validity? 2) Do I want a regular expression to find certain things in my string? 3) Do I want a regular expression so that I can replace patterns in my string? There can be some...

It has been a while since my last post. Things get crazy at times. But, here is another bit of sample code for you to muse over. We will look at enumerations and strings. In C#, an enumeration is NOT a string, nor can you define it to be one. An enumeration can be defined as any of a number of integer types. You can leave it as its default type... public enum unspecifiedTypeEnum { one = 1, two, three, } In which case you get named 32 bit values. Or you can specify the type of the underlying value as byte , sbyte , ushort , short , uint , int , ulong or long ... public enum byteTypeEnum : byte { one = 1, two, three, } // or... public enum ushortTypeEnum : ushort { one = 1, two, three, } // etc... ... But, you can't declare it as a string. That doesn't mean you can't use strings at all. When I want to save data to a file for future reference, I like to make my enumerations human readable and store them...

Suppose you've been given the task to write a function that copies the contents of one folder to another. So you set off on your merry way and come up with something like the following. using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Windows.Forms; using System.IO; namespace ThreadPoolPart4 { public partial class Form1 : Form { public Form1() { InitializeComponent(); } private void button1_Click(object sender, EventArgs e) { // Get the Folder names, copy contents from one to the other FolderBrowserDialog fb = new FolderBrowserDialog(); fb.ShowDialog(); string src = fb.SelectedPath; fb.ShowDialog(); string dst = fb.SelectedPath; // no error checking on the names, this is an example only if (dst != src)...

You are trying to come up to speed in C# fast. Then all of a sudden, you come across the C# Generic Type and wonder how do I master that. Well, I've got some good news for you. You are in good company. You thought I was going to say I'll help you master generics. No, that's beyond a simple blog like mine. But, maybe I can help you become proficient. We just have to get the main learning hurdles out of the way. Hurdle #1 - Rationale Generic Types were added to C# in version 2.0. Now, I am not going to go into any detail on the history of C# or generics. I just mention this because the C# team decided they had a serious enough short coming in 1.1 to add this major feature. That is, many, many programmers were opting to ditch type-safety and decent performance in order to write more versatile data structures. How's that? Well, folks (MS included) were writing things like List and Queue and Stack to take "objects". Then their particular data structure ...

When I first started programming, I thought "Sleep" to be one of the most useless calls I could make. No, I'm not talking about personal habits, I'm talking about the Sleep() function. using System.Threading; Thread.Sleep(int milliSeconds) We find this little "do nothing" function in C, C++, C#, VB, VB.Net, WScipt, and similar functions in other languages. And, I have since come to understand how useful and confusing "doing nothing" can be. So, let's take a look at it; I'll be focusing on the C# Sleep() function. Sleep() simply suspends the execution of your thread for a specific period of time. It relinquishes the remainder of its time-slice and becomes "unrunnable" for a period of time. If the time period is zero, it relinquish its time-slice only if another thread is ready and waiting to run. If there are no waiting threads, and the time span is zero, the calling thread remains ready to run and therefore returns from Slee...