String.ToUpperInvariant Method

Returns a copy of this String object converted to uppercase using the casing rules of the invariant culture.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

public string ToUpperInvariant()

Return Value

Type: System.String
The uppercase equivalent of the current string.

The invariant culture represents a culture that is culture-insensitive. It is associated with the English language but not with a specific country or region. For more information, see the CultureInfo.InvariantCulture property.

If your application depends on the case of a string changing in a predictable way that is unaffected by the current culture, use the ToUpperInvariant method. The ToUpperInvariant method is equivalent to ToUpper(CultureInfo.InvariantCulture). The method is recommended when a collection of strings must appear in a predictable order in a user interface control.

NoteNote

This method does not modify the value of the current instance. Instead, it returns a new string in which all characters in the current instance are converted to uppercase.

Security Considerations

If you need the lowercase or uppercase version of an operating system identifier, such as a file name, named pipe, or registry key, use the ToLowerInvariant or ToUpperInvariant methods.

The following example defines a string array that contains a single word in a number of languages. The ToUpperInvariant method is used to populate the elements of a parallel array with the case-insensitive version of each word. The Array.Sort<TKey, TValue>(TKey[], TValue[], IComparer<TKey>) method is used to sort the case-sensitive array based on the order of elements in the uppercase array to ensure that elements appear in the same order regardless of language.

using System;
using System.IO;

public class Example
{
   public static void Main()
   {
      string[] words = { "Tuesday", "Salı", "Вторник", "Mardi", 
                         "Τρίτη", "Martes", "יום שלישי", 
                         "الثلاثاء", "วันอังคาร" };
      StreamWriter sw = new StreamWriter(@".\output.txt");

      // Display array in unsorted order. 
      foreach (string word in words)
         sw.WriteLine(word);

      sw.WriteLine();

      // Create parallel array of words by calling ToUpperInvariant. 
      string[] upperWords = new string[words.Length];
      for (int ctr = words.GetLowerBound(0); ctr <= words.GetUpperBound(0); ctr++)
         upperWords[ctr] = words[ctr].ToUpperInvariant();

      // Sort the words array based on the order of upperWords.
      Array.Sort(upperWords, words, StringComparer.InvariantCulture);

      // Display the sorted array. 
      foreach (string word in words)
         sw.WriteLine(word);

      sw.Close();      
   }
}
// The example produces the following output: 
//       Tuesday 
//       Salı 
//       Вторник 
//       Mardi 
//       Τρίτη 
//       Martes 
//       יום שלישי 
//       الثلاثاء 
//       วันอังคาร 
//        
//       Mardi 
//       Martes 
//       Salı 
//       Tuesday 
//       Τρίτη 
//       Вторник 
//       יום שלישי 
//       الثلاثاء 
//       วันอังคาร

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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