C# 正則表達式完全指南

C#通過 System.Text.RegularExpressions 命名空間提供強大的正則表達式支持。本指南將詳細介紹C#中正則表達式的使用方法、性能優(yōu)化和最佳實踐。

1. 基礎(chǔ)知識

1.1 命名空間導入

using System.Text.RegularExpressions;

1.2 基本使用

public class RegexBasics
{public void BasicExamples(){string text = "Hello, my phone is 123-456-7890";// 創(chuàng)建正則表達式對象Regex regex = new Regex(@"\d+");// 檢查是否匹配bool isMatch = regex.IsMatch(text);// 查找第一個匹配Match match = regex.Match(text);if (match.Success){Console.WriteLine($"Found: {match.Value}");}// 查找所有匹配MatchCollection matches = regex.Matches(text);foreach (Match m in matches){Console.WriteLine($"Found: {m.Value}");}}
}

1.3 正則表達式選項

public class RegexOptions
{public void OptionsExample(){// 不區(qū)分大小寫Regex caseInsensitive = new Regex(@"hello", RegexOptions.IgnoreCase);// 多行模式Regex multiline = new Regex(@"^start", RegexOptions.Multiline);// 忽略空白字符和注釋Regex ignored = new Regex(@"\d+  # 匹配數(shù)字\s*  # 可選的空白字符\w+  # 匹配單詞", RegexOptions.IgnorePatternWhitespace);// 編譯正則表達式以提高性能Regex compiled = new Regex(@"\d+", RegexOptions.Compiled);}
}

2. 正則表達式語法

2.1 字符匹配

public class CharacterMatching
{public void MatchingExamples(){string text = "C# 10.0 is awesome! Price: $99.99";// 匹配數(shù)字Regex digits = new Regex(@"\d+");foreach (Match m in digits.Matches(text)){Console.WriteLine($"Number: {m.Value}");}// 匹配單詞Regex words = new Regex(@"\w+");var wordMatches = words.Matches(text).Cast<Match>().Select(m => m.Value).ToList();// 匹配空白字符string[] parts = Regex.Split(text, @"\s+");// 自定義字符類Regex vowels = new Regex(@"[aeiou]", RegexOptions.IgnoreCase);var vowelMatches = vowels.Matches(text).Cast<Match>().Select(m => m.Value).ToList();}
}

2.2 分組和捕獲

public class GroupingExample
{public void GroupExamples(){string text = "John Smith, Jane Doe, Bob Johnson";// 基本分組Regex regex = new Regex(@"(\w+)\s(\w+)");foreach (Match match in regex.Matches(text)){Console.WriteLine($"Full name: {match.Groups[0].Value}");Console.WriteLine($"First name: {match.Groups[1].Value}");Console.WriteLine($"Last name: {match.Groups[2].Value}");}// 命名分組Regex namedRegex = new Regex(@"(?<first>\w+)\s(?<last>\w+)");foreach (Match match in namedRegex.Matches(text)){Console.WriteLine($"First: {match.Groups["first"].Value}");Console.WriteLine($"Last: {match.Groups["last"].Value}");}}
}

3. 高級特性

3.1 替換操作

public class ReplacementOperations
{public string ReplaceExample(string text){// 簡單替換string result1 = Regex.Replace(text, @"\d+", "X");// 使用MatchEvaluator委托string result2 = Regex.Replace(text, @"\d+", match =>{int number = int.Parse(match.Value);return (number * 2).ToString();});// 使用命名組的替換Regex regex = new Regex(@"(?<first>\w+)\s(?<last>\w+)");string result3 = regex.Replace(text, "${last}, ${first}");return result3;}
}

3.2 前瞻和后顧

public class LookAroundExample
{public void LookAroundDemo(){string text = "Price: $100, Cost: $50";// 正向前瞻Regex positiveAhead = new Regex(@"\d+(?=\s*dollars)");// 負向前瞻Regex negativeAhead = new Regex(@"\d+(?!\s*dollars)");// 正向后顧Regex positiveBehind = new Regex(@"(?<=\$)\d+");// 負向后顧Regex negativeBehind = new Regex(@"(?<!\$)\d+");}
}

4. 實用工具類

4.1 驗證器

public class Validator
{private static readonly Regex EmailRegex = new Regex(@"^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$",RegexOptions.Compiled);private static readonly Regex PhoneRegex = new Regex(@"^1[3-9]\d{9}$",RegexOptions.Compiled);private static readonly Regex PasswordRegex = new Regex(@"^(?=.*[A-Za-z])(?=.*\d)[A-Za-z\d]{8,}$",RegexOptions.Compiled);public static bool IsValidEmail(string email){if (string.IsNullOrEmpty(email)) return false;return EmailRegex.IsMatch(email);}public static bool IsValidPhone(string phone){if (string.IsNullOrEmpty(phone)) return false;return PhoneRegex.IsMatch(phone);}public static bool IsValidPassword(string password){if (string.IsNullOrEmpty(password)) return false;return PasswordRegex.IsMatch(password);}
}

4.2 文本處理器

public class TextProcessor
{private static readonly Regex UrlRegex = new Regex(@"https?://(?:[-\w.]|(?:%[\da-fA-F]{2}))+[^\s]*",RegexOptions.Compiled);private static readonly Regex HtmlTagRegex = new Regex(@"<[^>]+>",RegexOptions.Compiled);public static IEnumerable<string> ExtractUrls(string text){if (string.IsNullOrEmpty(text)) return Enumerable.Empty<string>();return UrlRegex.Matches(text).Cast<Match>().Select(m => m.Value);}public static string StripHtmlTags(string html){if (string.IsNullOrEmpty(html)) return string.Empty;return HtmlTagRegex.Replace(html, string.Empty);}public static string CleanWhitespace(string text){if (string.IsNullOrEmpty(text)) return string.Empty;return Regex.Replace(text.Trim(), @"\s+", " ");}
}

5. 性能優(yōu)化

5.1 靜態(tài)編譯正則表達式

public class RegexOptimization
{// 使用靜態(tài)字段存儲編譯后的正則表達式private static readonly Regex CompiledRegex = new Regex(@"\d+",RegexOptions.Compiled);// 使用Lazy<T>延遲初始化private static readonly Lazy<Regex> LazyRegex = new Lazy<Regex>(() => new Regex(@"\d+", RegexOptions.Compiled));public void OptimizedExample(){// 使用編譯后的正則表達式bool isMatch = CompiledRegex.IsMatch("123");// 使用延遲初始化的正則表達式bool lazyMatch = LazyRegex.Value.IsMatch("123");}
}

5.2 性能考慮

public class PerformanceConsiderations
{// 1. 使用適當?shù)倪x項private static readonly Regex FastRegex = new Regex(@"\d+",RegexOptions.Compiled | RegexOptions.ExplicitCapture);// 2. 避免過度使用通配符private static readonly Regex BetterRegex = new Regex(@"[^/]*foo[^/]*",  // 比 .*foo.* 更高效RegexOptions.Compiled);// 3. 使用非捕獲組private static readonly Regex NonCapturingRegex = new Regex(@"(?:\d+)(?:[a-z]+)",  // 使用(?:)表示非捕獲組RegexOptions.Compiled);
}

6. 異常處理

public class RegexExceptionHandling
{public static Regex CreateSafeRegex(string pattern){try{return new Regex(pattern, RegexOptions.Compiled);}catch (ArgumentException ex){throw new ArgumentException($"Invalid regex pattern: {ex.Message}", ex);}}public static bool SafeIsMatch(string input, string pattern){try{return Regex.IsMatch(input, pattern);}catch (RegexMatchTimeoutException ex){Console.WriteLine($"Regex matching timed out: {ex.Message}");return false;}catch (ArgumentException ex){Console.WriteLine($"Invalid regex pattern: {ex.Message}");return false;}}
}

7. 單元測試

[TestClass]
public class ValidatorTests
{[TestMethod]public void TestEmailValidation(){Assert.IsTrue(Validator.IsValidEmail("test@example.com"));Assert.IsTrue(Validator.IsValidEmail("user@domain.co.uk"));Assert.IsFalse(Validator.IsValidEmail("invalid.email"));Assert.IsFalse(Validator.IsValidEmail("@domain.com"));}[TestMethod]public void TestPhoneValidation(){Assert.IsTrue(Validator.IsValidPhone("13812345678"));Assert.IsFalse(Validator.IsValidPhone("12345678"));Assert.IsFalse(Validator.IsValidPhone("2381234567"));}[TestMethod]public void TestTextProcessing(){string html = "<p>Hello</p><div>World</div>";Assert.AreEqual("HelloWorld",TextProcessor.StripHtmlTags(html));string text = "  multiple   spaces   here  ";Assert.AreEqual("multiple spaces here",TextProcessor.CleanWhitespace(text));}
}

總結(jié)

C#的正則表達式實現(xiàn)具有以下特點：

1. 強大的Regex類支持
2. 編譯選項提供高性能
3. LINQ集成
4. 完整的Unicode支持

最佳實踐：

1. 使用靜態(tài)編譯的Regex對象提高性能
2. 合理使用RegexOptions
3. 處理超時和異常情況
4. 編寫完整的單元測試
5. 使用命名捕獲組提高可讀性

注意事項：

1. Regex對象創(chuàng)建開銷大，應(yīng)該重用
2. 考慮使用Compiled選項提高性能
3. 處理RegexMatchTimeoutException
4. 注意內(nèi)存使用

記住：在C#中使用正則表達式時，要充分利用.NET框架提供的功能，如編譯選項和LINQ集成。合理使用靜態(tài)編譯和緩存可以顯著提高性能。