Char Structure

A String object is a sequential collection of Char structures that represents a string of text. Most Unicode characters can be represented by a single Char object, but a character that is encoded as a base character, surrogate pair, and/or combining character sequence is represented by multiple Char objects. For this reason, a Char structure in a String object is not necessarily equivalent to a single Unicode character.

Multiple 16-bit code units are used to represent single Unicode characters in the following cases:

• Glyphs, which may consist of a single character or of a base character followed by one or more combining characters. For example, the character ä is represented by a Char object whose code unit is U+0061 followed by a Char object whose code unit is U+0308. (The character ä can also be defined by a single Char object that has a code unit of U+00E4.) The following example illustrates that the character ä consists of two Char objects.

  C#

  VB

  Copy

  
  using System;
  using System.IO;
  
  public class Example
  {
     public static void Main()
     {
        StreamWriter sw = new StreamWriter("chars1.txt");
        char[] chars = { '\u0061', '\u0308' };
        string strng = new String(chars);
        sw.WriteLine(strng); 
        sw.Close();
     }
  }
  // The example produces the following output:
  //       ä
  
  
  

• Characters outside the Unicode Basic Multilingual Plane (BMP). Unicode supports sixteen planes in addition to the BMP, which represents plane 0. A Unicode code point is represented in UTF-32 by a 21-bit value that includes the plane. For example, U+1D160 represents the MUSICAL SYMBOL EIGHTH NOTE character. Because UTF-16 encoding has only 16 bits, characters outside the BMP are represented by surrogate pairs in UTF-16. The following example illustrates that the UTF-32 equivalent of U+1D160, the MUSICAL SYMBOL EIGHTH NOTE character, is U+D834 U+DD60. U+D834 is the high surrogate; high surrogates range from U+D800 through U+DBFF. U+DD60 is the low surrogate; low surrogates range from U+DC00 through U+DFFF.

  C#

  VB

  Copy

  
  using System;
  using System.IO;
  
  public class Example
  {
     public static void Main()
     {
        StreamWriter sw = new StreamWriter(@".\chars2.txt");
        int utf32 = 0x1D160;
        string surrogate = Char.ConvertFromUtf32(utf32);
        sw.WriteLine("U+{0:X6} UTF-32 = {1} ({2}) UTF-16", 
                     utf32, surrogate, ShowCodePoints(surrogate));
        sw.Close();                    
     }
  
     private static string ShowCodePoints(string value)
     {
        string retval = null;
        foreach (var ch in value)
           retval += String.Format("U+{0:X4} ", Convert.ToUInt16(ch));
  
        return retval.Trim();
     }
  }
  // The example produces the following output:
  //       U+01D160 UTF-32 = ð (U+D834 U+DD60) UTF-16
  
  
  

Because a single character can be represented by multiple Char objects, we recommend that you use strings instead of individual characters to represent and analyze linguistic content.

The Char structure provides methods to compare Char objects, convert the value of the current Char object to an object of another type, and determine the Unicode category of a Char object:

• Use the CompareTo and Equals methods to compare Char objects.

• Use the ConvertFromUtf32 method to convert a code point to a string. Use the ConvertToUtf32 methods to convert a Char object or a surrogate pair of Char objects to a code point.

• Use the GetUnicodeCategory methods to get the Unicode category of a character. Use the IsControl, IsDigit, IsHighSurrogate, IsLetter, IsLetterOrDigit, IsLower, IsLowSurrogate, IsNumber, IsPunctuation, IsSeparator, IsSurrogate, IsSurrogatePair, IsSymbol, IsUpper, and IsWhiteSpace methods to determine whether a character is in a particular Unicode category such as digit, letter, punctuation, control character, and so on.

• Use the GetNumericValue methods to convert a Char object that represents a number to a numeric value type. Use Parse and TryParse to convert a character in a string into a Char object. Use ToString to convert a Char object to a String object.

• Use the ToLower, ToLowerInvariant, ToUpper, and ToUpperInvariant methods to change the case of a Char object.