C# 正则表达式完全指南

C# 正则表达式完全指南

C#通过 System.Text.RegularExpressions 命名空间提供强大的正则表达式支持。本指南将详细介绍C#中正则表达式的使用方法、性能优化和最佳实践。

1. 基础知识

1.1 命名空间导入

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";// 创建正则表达式对象Regex regex = new Regex(@"\d+");// 检查是否匹配bool isMatch = regex.IsMatch(text);// 查找第一个匹配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 正则表达式选项

public class RegexOptions
{public void OptionsExample(){// 不区分大小写Regex caseInsensitive = new Regex(@"hello", RegexOptions.IgnoreCase);// 多行模式Regex multiline = new Regex(@"^start", RegexOptions.Multiline);// 忽略空白字符和注释Regex ignored = new Regex(@"\d+  # 匹配数字\s*  # 可选的空白字符\w+  # 匹配单词", RegexOptions.IgnorePatternWhitespace);// 编译正则表达式以提高性能Regex compiled = new Regex(@"\d+", RegexOptions.Compiled);}
}

2. 正则表达式语法

2.1 字符匹配

public class CharacterMatching
{public void MatchingExamples(){string text = "C# 10.0 is awesome! Price: $99.99";// 匹配数字Regex digits = new Regex(@"\d+");foreach (Match m in digits.Matches(text)){Console.WriteLine($"Number: {m.Value}");}// 匹配单词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+");// 自定义字符类Regex vowels = new Regex(@"[aeiou]", RegexOptions.IgnoreCase);var vowelMatches = vowels.Matches(text).Cast<Match>().Select(m => m.Value).ToList();}
}

2.2 分组和捕获

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

3. 高级特性

3.1 替换操作

public class ReplacementOperations
{public string ReplaceExample(string text){// 简单替换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();});// 使用命名组的替换Regex regex = new Regex(@"(?<first>\w+)\s(?<last>\w+)");string result3 = regex.Replace(text, "${last}, ${first}");return result3;}
}

3.2 前瞻和后顾

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

4. 实用工具类

4.1 验证器

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 文本处理器

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. 性能优化

5.1 静态编译正则表达式

public class RegexOptimization
{// 使用静态字段存储编译后的正则表达式private static readonly Regex CompiledRegex = new Regex(@"\d+",RegexOptions.Compiled);// 使用Lazy<T>延迟初始化private static readonly Lazy<Regex> LazyRegex = new Lazy<Regex>(() => new Regex(@"\d+", RegexOptions.Compiled));public void OptimizedExample(){// 使用编译后的正则表达式bool isMatch = CompiledRegex.IsMatch("123");// 使用延迟初始化的正则表达式bool lazyMatch = LazyRegex.Value.IsMatch("123");}
}

5.2 性能考虑

public class PerformanceConsiderations
{// 1. 使用适当的选项private static readonly Regex FastRegex = new Regex(@"\d+",RegexOptions.Compiled | RegexOptions.ExplicitCapture);// 2. 避免过度使用通配符private static readonly Regex BetterRegex = new Regex(@"[^/]*foo[^/]*",  // 比 .*foo.* 更高效RegexOptions.Compiled);// 3. 使用非捕获组private static readonly Regex NonCapturingRegex = new Regex(@"(?:\d+)(?:[a-z]+)",  // 使用(?:)表示非捕获组RegexOptions.Compiled);
}

6. 异常处理

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. 单元测试

[TestClass]
public class ValidatorTests
{[TestMethod]public void TestEmailValidation(){Assert.IsTrue(Validator.IsValidEmail("[e-mail]"));Assert.IsTrue(Validator.IsValidEmail("[e-mail]"));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));}
}

总结

C#的正则表达式实现具有以下特点：

1. 强大的Regex类支持
2. 编译选项提供高性能
3. LINQ集成
4. 完整的Unicode支持

最佳实践：

1. 使用静态编译的Regex对象提高性能
2. 合理使用RegexOptions
3. 处理超时和异常情况
4. 编写完整的单元测试
5. 使用命名捕获组提高可读性

注意事项：

1. Regex对象创建开销大，应该重用
2. 考虑使用Compiled选项提高性能
3. 处理RegexMatchTimeoutException
4. 注意内存使用

记住：在C#中使用正则表达式时，要充分利用.NET框架提供的功能，如编译选项和LINQ集成。合理使用静态编译和缓存可以显著提高性能。