Ngoc Thanh

In this final part, we’ll ensure your regex patterns are not only powerful — but also testable , debuggable , and maintainable . We’ll cover: Why testing regex matters Writing unit tests for regex in C# Using online regex testers Visual debugging techniques Common mistakes and how to catch them .NET tools and Visual Studio support Building your own test harness 11.1 Why Test Regular Expressions? Regex is easy to write but hard to maintain . A working pattern can: Break silently Be too greedy Miss edge cases Match unintended inputs Tests act as a safety net . 11.2 Writing Unit Tests for Regex in C# Use your test framework of choice (e.g., MSTest, xUnit, NUnit). ✅ Example with xUnit: public class EmailRegexTests { [Theory] [InlineData("john@example.com", true)] [InlineData("bademail@", false)] public void TestEmailPattern ( string in...

C# goes beyond standard regex usage — it gives you tools to compile and cache patterns into strongly-typed classes using RegexCompilationInfo, which boosts performance and lets you bundle regex logic in a reusable way. In this part, you’ll learn: How the .NET regex engine works under the hood How to create precompiled regex classes using RegexCompilationInfo Caching strategies Performance considerations When to compile vs. interpret 10.1 How the .NET Regex Engine Works Interpreted vs Compiled Mode Interpreted : default; parses and evaluates the regex every time. Compiled : transforms regex into IL (intermediate language) code. Key Options: RegexOptions.Compiled RegexOptions.IgnoreCase RegexOptions.Singleline RegexOptions.ExplicitCapture Compiled trades memory for speed — ideal for regexes used frequently. 10.2 Regex Compilation via RegexCompilationInfo You can precompile regex into standalone C# classe...

Regular Expressions are powerful — but with great power comes great potential for bugs, performance issues, and maintenance nightmares . In this part, you’ll learn how to avoid traps and write smarter, safer regex in C#. 9.1 Catastrophic Backtracking ❌ Problem: Poorly written patterns with nested quantifiers can take exponential time. Example: var pattern = @"^(a+)+$" ; var input = new string ( 'a' , 10000 ) + "!" ; Regex.IsMatch(input, pattern); // ❗ Will hang or be super slow ✅ Solution: Use atomic groups or lazy quantifiers. Or redesign. var safePattern = @"^a+$" ; Avoid unbounded nested quantifiers like (a+)+, (.*)+, (.+)+. 9.2 Greedy vs Lazy Quantifiers ❌ Greedy Example: var input = "<tag>Hello</tag><tag>World</tag>" ; var pattern = "<tag>.*</tag>" ; var matches = Regex.Matches(input, pattern); // Returns one big match ...

Why This Matters Writing regex is one thing — making sure it's correct, fast, and maintainable is another. In this part, you’ll learn: How to test regex patterns in Visual Studio How to debug regex with online tools How to write unit tests for regex How to benchmark regex performance How to use .NET libraries for regex diagnostics How to build a live regex tester inside your own app 8.1 Testing Regex in Visual Studio ✅ Steps: Open any .cs file. Write a regex as a string: var pattern = @"\d{4}-\d{2}-\d{2}" ; Hover over it → Visual Studio (2022+) shows a preview. Use Quick Actions > Test Regex to open the test window. ✨ Features: Test input against the pattern. Toggle multiline, ignore case, etc. See groups and matches live. 8.2 Online Regex Testers 🔧 Regex101.com Supports flavor selection (choose ".NET") Highli...