Example of when the culture parameter of string.Equals (c#) actually makes a difference?

Question

I don’t fully understand the second parameter of string.Equals, and this is because I can’t find any examples of when it would actually make a difference. For example, the example given here is the same, regardless of the value of the second parameter (aside from IgnoreCase): http://msdn.microsoft.com/en-us/library/c64xh8f9.aspx

I am just talking about the values StringComparison.CurrentCulture, InvariantCulture, or Ordinal.
I can understand the difference between these and their IgnoreCase equivalents.

Answer 1

This MSDN page (Best Practices for Using Strings in the .NET Framework) has a lot of information about using strings and the following example is taken from it:

using System;
using System.Globalization;
using System.Threading;

public class Example
{
   public static void Main()
   {
      string[] values= { "able", "ångström", "apple", "Æble", 
                         "Windows", "Visual Studio" };
      Array.Sort(values);
      DisplayArray(values);

      // Change culture to Swedish (Sweden).
      string originalCulture = CultureInfo.CurrentCulture.Name;
      Thread.CurrentThread.CurrentCulture = new CultureInfo("sv-SE");
      Array.Sort(values);
      DisplayArray(values);

      // Restore the original culture.
      Thread.CurrentThread.CurrentCulture = new CultureInfo(originalCulture);
    }

    private static void DisplayArray(string[] values)
    {
      Console.WriteLine("Sorting using the {0} culture:",  
                        CultureInfo.CurrentCulture.Name);
      foreach (string value in values)
         Console.WriteLine("   {0}", value);

      Console.WriteLine();
    }
}
// The example displays the following output:
//       Sorting using the en-US culture:
//          able
//          Æble
//          ångström
//          apple
//          Visual Studio
//          Windows
//       
//       Sorting using the sv-SE culture:
//          able
//          Æble
//          apple
//          Windows
//          Visual Studio
//          ångström

Answer 2

Differences between StringComparison.InvariantCulture and StringComparison.Ordinal are fairly easy to find, since Ordinal means that the string is not normalized before it is compared. So we just have to compare a normalized string to an unnormalized string.

Finding differences between StringComparison.InvariantCulture and StringComparison.CurrentCulture (or differences between different CurrentCultures) is a bit more difficult, but they do exist.

Here is one example:

    string a = "\u00C4";       // "LATIN CAPITAL LETTER A WITH DIAERESIS"
    string b = "\u0041\u0308"; // "LATIN CAPITAL LETTER A" - "COMBINING DIAERESIS"

    Console.WriteLine(a.Equals(b, StringComparison.InvariantCulture)); // true

    Thread.CurrentThread.CurrentCulture = new CultureInfo("en-US", false);
    Console.WriteLine(a.Equals(b, StringComparison.CurrentCulture));   // true

    Thread.CurrentThread.CurrentCulture = new CultureInfo("da-DK", false);
    Console.WriteLine(a.Equals(b, StringComparison.CurrentCulture));   // false

    Console.WriteLine(a.Equals(b, StringComparison.Ordinal));          // false

Or this one that only uses ASCII characters:

    string ddzs = "ddzs";
    string dzsdzs = "dzsdzs";

    Thread.CurrentThread.CurrentCulture = new CultureInfo("en-US", false);
    Console.WriteLine(ddzs.Equals(dzsdzs, StringComparison.CurrentCulture)); // false

    Thread.CurrentThread.CurrentCulture = new CultureInfo("hu-HU", false);
    Console.WriteLine(ddzs.Equals(dzsdzs, StringComparison.CurrentCulture)); // true