字符串与正则表达式

1. C#中string关键字的映射实际上指向.NET基类System .String 。
2. 使用string连接两个字符串实际上是创建了一个新字符串实例，把两部分内容复制到新字符串中。
3. 在StringBuilder上可以进行的处理仅限于替换和添加或删除字符串中的文本，但它的工作方式非常高效。StringBuilder类基本上应在处理多个字符串时使用，如果只是连接两个字符串，使用System.String会比较好。
4. 不能把StringBuilder转换为String。如果要把StringBuilder的内容输出为String，唯一的方式是使用ToString()方法。
5. 正则表达式示例：

 

 

using System;
using System.Collections.Generic;
using System.Text;
using System.Text.RegularExpressions;

namespace Wrox.ProCSharp.RegularExpressionPlayaround
{
   class MainEntryPoint
   {
      static void Main()
      {
         Find1();
         Console.ReadLine();
      }

      static void Find1()
      {
         string text = @"XML has made a major impact in almost every aspect of software 
                         development. Designed as an open, extensible, self-describing 
                         language, it has become the standard for data and document delivery 
                         on the web. The panoply of XML-related technologies continues to 
                         develop at breakneck speed, to enable validation, navigation, 
                         transformation, linking, querying, description, and messaging of data.";
         string pattern = @"\bn\S*ion\b";
         MatchCollection matches = Regex.Matches(text, pattern, RegexOptions.IgnoreCase | 
                        RegexOptions.IgnorePatternWhitespace | RegexOptions.ExplicitCapture);
         WriteMatches(text, matches);
      }        

      static void Find2()
      {
         string text = @"XML has made a major impact in almost every aspect of software 
                         development. Designed as an open, extensible, self-describing 
                         language, it has become the standard for data and document delivery 
                         on the web. The panoply of XML-related technologies continues to 
                         develop at breakneck speed, to enable validation, navigation, 
                         transformation, linking, querying, description, and messaging of data.";
         string pattern = @"\bn";
         MatchCollection matches = Regex.Matches(text, pattern, RegexOptions.IgnoreCase);
         WriteMatches(text, matches);
      }
 
      static void WriteMatches(string text, MatchCollection matches)
      {
         Console.WriteLine("Original text was: \n\n" + text + "\n");
         Console.WriteLine("No. of matches: " + matches.Count);
         foreach (Match nextMatch in matches)
         {
            int Index = nextMatch.Index;
            string result = nextMatch.ToString();
            int charsBefore = (Index < 5) ? Index : 5;
            int fromEnd = text.Length - Index - result.Length;
            int charsAfter = (fromEnd < 5) ? fromEnd : 5;
            int charsToDisplay = charsBefore + charsAfter + result.Length;
            Console.WriteLine("Index: {0}, \tString: {1}, \t{2}", Index, result,  
                                  text.Substring(Index - charsBefore, charsToDisplay));
         }
      }
   }
}