//引入命名空间
using System;
using System.Reflection;

[assembly: AssemblyVersion("1.0.0.0")]

public static class StringLibrary
{
   public static int SubstringStartsAt(String fullString, String substr)
   {
      return fullString.IndexOf(substr, StringComparison.Ordinal);
   }
}

//引入命名空间
using System;

public class Example
{
   public static void Main()
   {
      String value = "The archaeologist";
      String substring = "archæ";
      int position = StringLibrary.SubstringStartsAt(value, substring); 
      if (position >= 0) 
         Console.WriteLine("'{0}' found in '{1}' starting at position {2}",
                        substring, value, position);
      else
         Console.WriteLine("'{0}' not found in '{1}'", substring, value);
   }
}

//引入命名空间
using System;
using System.Reflection;

[assembly: AssemblyVersion("2.0.0.0")]

public static class StringLibrary
{
   public static int SubstringStartsAt(String fullString, String substr)
   {
      return fullString.IndexOf(substr, StringComparison.CurrentCulture);
   }
}

//引入命名空间
using System;
using System.Reflection;

[assembly: AssemblyVersion("2.0.0.0")]

public static class StringLibrary
{
   public static int SubstringStartsAt(String fullString, String substr)
   {
      bool flag;
      if (AppContext.TryGetSwitch("StringLibrary.DoNotUseCultureSensitiveComparison", out flag) && flag == true)
         return fullString.IndexOf(substr, StringComparison.Ordinal);
      else
         return fullString.IndexOf(substr, StringComparison.CurrentCulture);
   }
}

//引入命名空间
using System;
using System.IO;
using System.Runtime.Versioning;

[assembly:TargetFramework(".NETFramework,Version=v4.6.2")]

public class Example
{
   public static void Main()
   {
      Console.WriteLine(Path.GetDirectoryName("file://c/temp/dirlist.txt")); 
   }
}