ToLower vs ToLowerInvariant

Question

I'm just looking for any example that this two methods produces different results. First of all, I visit msdn page, and run code from it with minor changes

using System;
using System.Globalization;
using System.Linq;

class Program
{
    static void Main()
    {
        string[] words = { "Tuesday", "Salı", "Вторник", "Mardi", 
                         "Τρίτη", "Martes", "יום שלישי", 
                         "الثلاثاء", "วันอังคาร" };
        Console.BufferHeight = 1000;
        var test = CultureInfo.GetCultures(CultureTypes.AllCultures)
                              .Select(ci =>
                                      {
                                          string[] wordsToLower = words.Select(x => x.ToLower(ci)).ToArray();
                                          string[] wordsToLowerInvariant = words.Select(x => x.ToLowerInvariant()).ToArray();
                                          return new
                                                 {
                                                     Culture = ci,
                                                     ToLowerDiffers = !wordsToLower.SequenceEqual(wordsToLowerInvariant)
                                                 };
                                      })
                              .ToArray();
        foreach (var x in test)
        {
            Console.WriteLine("Culture {0}, ToLower and ToLowerInvariant produces different results: {1}", x.Culture, x.ToLowerDiffers);
        }
        Console.WriteLine();
        Console.WriteLine("Difference exists for any ToLower call: {0}", test.Any(x => x.ToLowerDiffers));
    }
}

But here I have a problem: this code produces the same output for ToLower and ToLowerInvariant calls in all existing cultures.

So question is: there is any string that produces different results for this test?

Have you seen [this other question](http://stackoverflow.com/q/16797597/50447) or [this answer](http://stackoverflow.com/a/26895380/50447)? — Rowland Shaw, Jun 11 '15 at 10:37
"Turkish i problem" http://blog.codinghorror.com/whats-wrong-with-turkey/ — Dennis_E, Jun 11 '15 at 10:38
Another nice read http://www.moserware.com/2008/02/does-your-code-pass-turkey-test.html — Dolgsthrasir, Jun 11 '15 at 10:41

score 7 · Accepted Answer · answered Jun 11 '15 at 10:38

7

Try the Turkish dotted İ:

var culture = new CultureInfo("tr-TR");

string test = "İ";

if (test.ToLower(culture) == test.ToLowerInvariant())
    Console.WriteLine("Same");
else
    Console.WriteLine("Different"); // Prints this!

answered Jun 11 '15 at 10:38

Matthew Watson

104,400
10
158
276

More specifically, the normal ASCII 'i' capitalizes to a big dotted 'İ' if the user's culture is Turkish. If you don't want that behavior, avoid it by specifying a different culture, like the invariant one. – user1676558 Mar 12 '17 at 22:47

score 2 · Answer 2 · answered Jun 11 '15 at 10:50

2

xxxInvariant assumes culture setting as default. To be able to show the difference, you should demonstrate ToLower and ToLowerInvariant with a culture info that is different than the default culture in your setting. And by default, the default culture is the system culture.

So if your system's culture is en-US and you use only en-US characters in your code, ToLower and ToLowerInvariant will give the same result.

As far as I can tell, if you change "Salı" to "SALI" after ToLowerInvariant you should get "Sali".

answered Jun 11 '15 at 10:50

Gökhan Uslu

39
2

He is calling the override of `ToLower()` that takes a `CultureInfo` – Rowland Shaw Jun 11 '15 at 11:18
You are possibly wrong there? String.ToLower() uses the default culture while String.ToLowerInvariant() uses the invariant culture. So you are essentially asking the differences between invariant culture and ordinal string comparision. http://stackoverflow.com/a/6225872/742084 – Cel Oct 15 '16 at 09:10

ToLower vs ToLowerInvariant

2 Answers2