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String.ToUpper Method

Returns a copy of this string converted to uppercase.

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

public string ToUpper()

Return Value

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

This method uses the casing rules of the current culture to convert each character in the current instance to its uppercase equivalent. If a character does not have an uppercase equivalent, it is included unchanged in the returned string.

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.

The ToUpper method is often used to convert a string to uppercase so that it can be used in a case-insensitive comparison. A better method to perform case-insensitive comparison is to call a string comparison method that has a StringComparison parameter whose value you set to StringComparison.CurrentCultureIgnoreCase for a culture-sensitive, case-insensitive comparison.

Security Considerations

The casing operation that results from calling the ToUpper() method takes the casing conventions of the current culture into account. 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 method. This produces the same result in every culture (unlike the ToUpper() method) and performs more efficiently.

Notes to Callers

As explained in Best Practices for Using Strings in the .NET Framework, we recommend that you avoid calling string casing methods that substitute default values and instead call methods that require parameters to be explicitly specified. To convert a string to uppercase by using the casing conventions of the current culture, call the ToUpper(CultureInfo) method overload with a value of CultureInfo.CurrentCulture for its culture parameter.

The following example calls the ToUpper method to convert a series of one-character strings that contain each character in the Basic Latin, Latin-1 Supplement, and Latin Extended-A character sets. It then displays each string whose uppercase character is different from its lowercase character.

using System;

public class Example
{
   public static void Main()
   {
      int n = 0;
      for (int ctr = 0x20; ctr <= 0x017F; ctr++) {
         string string1 = Convert.ToChar(ctr).ToString();
         string upperString = string1.ToUpper();
         if (string1 != upperString) {
            Console.Write(@"{0} (\u+{1}) --> {2} (\u+{3})         ", 
                          string1, 
                          Convert.ToUInt16(string1[0]).ToString("X4"),  
                          upperString, 
                          Convert.ToUInt16(upperString[0]).ToString("X4"));                     
            n++;
            if (n % 2 == 0) Console.WriteLine();
         }
      } 
   }
}
// The example displays the following output: 
//    a (\u+0061) --> A (\u+0041)         b (\u+0062) --> B (\u+0042) 
//    c (\u+0063) --> C (\u+0043)         d (\u+0064) --> D (\u+0044) 
//    e (\u+0065) --> E (\u+0045)         f (\u+0066) --> F (\u+0046) 
//    g (\u+0067) --> G (\u+0047)         h (\u+0068) --> H (\u+0048) 
//    i (\u+0069) --> I (\u+0049)         j (\u+006A) --> J (\u+004A) 
//    k (\u+006B) --> K (\u+004B)         l (\u+006C) --> L (\u+004C) 
//    m (\u+006D) --> M (\u+004D)         n (\u+006E) --> N (\u+004E) 
//    o (\u+006F) --> O (\u+004F)         p (\u+0070) --> P (\u+0050) 
//    q (\u+0071) --> Q (\u+0051)         r (\u+0072) --> R (\u+0052) 
//    s (\u+0073) --> S (\u+0053)         t (\u+0074) --> T (\u+0054) 
//    u (\u+0075) --> U (\u+0055)         v (\u+0076) --> V (\u+0056) 
//    w (\u+0077) --> W (\u+0057)         x (\u+0078) --> X (\u+0058) 
//    y (\u+0079) --> Y (\u+0059)         z (\u+007A) --> Z (\u+005A) 
//    à (\u+00E0) --> À (\u+00C0)         á (\u+00E1) --> Á (\u+00C1) 
//    â (\u+00E2) --> Â (\u+00C2)         ã (\u+00E3) --> Ã (\u+00C3) 
//    ä (\u+00E4) --> Ä (\u+00C4)         å (\u+00E5) --> Å (\u+00C5) 
//    æ (\u+00E6) --> Æ (\u+00C6)         ç (\u+00E7) --> Ç (\u+00C7) 
//    è (\u+00E8) --> È (\u+00C8)         é (\u+00E9) --> É (\u+00C9) 
//    ê (\u+00EA) --> Ê (\u+00CA)         ë (\u+00EB) --> Ë (\u+00CB) 
//    ì (\u+00EC) --> Ì (\u+00CC)         í (\u+00ED) --> Í (\u+00CD) 
//    î (\u+00EE) --> Î (\u+00CE)         ï (\u+00EF) --> Ï (\u+00CF) 
//    ð (\u+00F0) --> Ð (\u+00D0)         ñ (\u+00F1) --> Ñ (\u+00D1) 
//    ò (\u+00F2) --> Ò (\u+00D2)         ó (\u+00F3) --> Ó (\u+00D3) 
//    ô (\u+00F4) --> Ô (\u+00D4)         õ (\u+00F5) --> Õ (\u+00D5) 
//    ö (\u+00F6) --> Ö (\u+00D6)         ø (\u+00F8) --> Ø (\u+00D8) 
//    ù (\u+00F9) --> Ù (\u+00D9)         ú (\u+00FA) --> Ú (\u+00DA) 
//    û (\u+00FB) --> Û (\u+00DB)         ü (\u+00FC) --> Ü (\u+00DC) 
//    ý (\u+00FD) --> Ý (\u+00DD)         þ (\u+00FE) --> Þ (\u+00DE) 
//    ÿ (\u+00FF) --> Ÿ (\u+0178)         ā (\u+0101) --> Ā (\u+0100) 
//    ă (\u+0103) --> Ă (\u+0102)         ą (\u+0105) --> Ą (\u+0104) 
//    ć (\u+0107) --> Ć (\u+0106)         ĉ (\u+0109) --> Ĉ (\u+0108) 
//    ċ (\u+010B) --> Ċ (\u+010A)         č (\u+010D) --> Č (\u+010C) 
//    ď (\u+010F) --> Ď (\u+010E)         đ (\u+0111) --> Đ (\u+0110) 
//    ē (\u+0113) --> Ē (\u+0112)         ĕ (\u+0115) --> Ĕ (\u+0114) 
//    ė (\u+0117) --> Ė (\u+0116)         ę (\u+0119) --> Ę (\u+0118) 
//    ě (\u+011B) --> Ě (\u+011A)         ĝ (\u+011D) --> Ĝ (\u+011C) 
//    ğ (\u+011F) --> Ğ (\u+011E)         ġ (\u+0121) --> Ġ (\u+0120) 
//    ģ (\u+0123) --> Ģ (\u+0122)         ĥ (\u+0125) --> Ĥ (\u+0124) 
//    ħ (\u+0127) --> Ħ (\u+0126)         ĩ (\u+0129) --> Ĩ (\u+0128) 
//    ī (\u+012B) --> Ī (\u+012A)         ĭ (\u+012D) --> Ĭ (\u+012C) 
//    į (\u+012F) --> Į (\u+012E)         ı (\u+0131) --> I (\u+0049) 
//    ij (\u+0133) --> IJ (\u+0132)         ĵ (\u+0135) --> Ĵ (\u+0134) 
//    ķ (\u+0137) --> Ķ (\u+0136)         ĺ (\u+013A) --> Ĺ (\u+0139) 
//    ļ (\u+013C) --> Ļ (\u+013B)         ľ (\u+013E) --> Ľ (\u+013D) 
//    ŀ (\u+0140) --> Ŀ (\u+013F)         ł (\u+0142) --> Ł (\u+0141) 
//    ń (\u+0144) --> Ń (\u+0143)         ņ (\u+0146) --> Ņ (\u+0145) 
//    ň (\u+0148) --> Ň (\u+0147)         ŋ (\u+014B) --> Ŋ (\u+014A) 
//    ō (\u+014D) --> Ō (\u+014C)         ŏ (\u+014F) --> Ŏ (\u+014E) 
//    ő (\u+0151) --> Ő (\u+0150)         œ (\u+0153) --> Œ (\u+0152) 
//    ŕ (\u+0155) --> Ŕ (\u+0154)         ŗ (\u+0157) --> Ŗ (\u+0156) 
//    ř (\u+0159) --> Ř (\u+0158)         ś (\u+015B) --> Ś (\u+015A) 
//    ŝ (\u+015D) --> Ŝ (\u+015C)         ş (\u+015F) --> Ş (\u+015E) 
//    š (\u+0161) --> Š (\u+0160)         ţ (\u+0163) --> Ţ (\u+0162) 
//    ť (\u+0165) --> Ť (\u+0164)         ŧ (\u+0167) --> Ŧ (\u+0166) 
//    ũ (\u+0169) --> Ũ (\u+0168)         ū (\u+016B) --> Ū (\u+016A) 
//    ŭ (\u+016D) --> Ŭ (\u+016C)         ů (\u+016F) --> Ů (\u+016E) 
//    ű (\u+0171) --> Ű (\u+0170)         ų (\u+0173) --> Ų (\u+0172) 
//    ŵ (\u+0175) --> Ŵ (\u+0174)         ŷ (\u+0177) --> Ŷ (\u+0176) 
//    ź (\u+017A) --> Ź (\u+0179)         ż (\u+017C) --> Ż (\u+017B) 
//    ž (\u+017E) --> Ž (\u+017D)

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.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

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: 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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