Char Structure

Article
01/16/2013

[This documentation is for preview only, and is subject to change in later releases. Blank topics are included as placeholders.]

Represents a character as a UTF-16 code unit.

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

Syntax

'Declaration
<SerializableAttribute> _
Public Structure Char

[SerializableAttribute]
public struct Char

[SerializableAttribute]
public value class Char

[<Sealed>]
[<SerializableAttribute>]
type Char =  struct end

JScript supports the use of structures, but not the declaration of new ones.

The Char type exposes the following members.

Methods

	Name	Description
	Equals	Indicates whether this instance and a specified object are equal. (Inherited from ValueType.)
	GetHashCode	Serves as a hash function for a particular type. (Inherited from Object.)
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	ToLower	Returns the lower case character.
	ToString	Converts the value of this instance to its equivalent string representation. (Overrides Object. . :: . .ToString() () () ().)
	ToUpper	Returns the upper case character.

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Fields

	Name	Description
	MaxValue	Represents the largest possible value of a Char. This field is constant.
	MinValue	Represents the smallest possible value of a Char. This field is constant.

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Remarks

The Char structure represents a Unicode character. The Unicode Standard identifies each Unicode character with a unique 21-bit scalar number called a code point, and defines the UTF-16 encoding form that specifies how a code point is encoded into a sequence of one or more 16-bit values. Each 16-bit value ranges from hexadecimal 0x0000 through 0xFFFF and is stored in a Char structure. The value of a Char object is its 16-bit numeric (ordinal) value.

Char Objects, Unicode Characters, and Strings

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.
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.

Characters and Text Elements

Because a single character can be represented by multiple Char objects, it is not always meaningful to work with individual Char objects. For instance, the following example converts the Unicode code points that represent the Aegean numbers zero through 9 to UTF-16 encoded code units. Because it erroneously equates Char objects with characters, it inaccurately reports that the resulting string has 20 characters.

You can do the following to avoid the assumption that a Char object represents a single character.

You can work with a String object in its entirety instead of working with its individual characters to represent and analyze linguistic content.
You can use the StringInfo class to work with text elements instead of individual Char objects. The following example uses the StringInfo object to count the number of text elements in a string that consists of the Aegean numbers zero through nine. Because it considers a surrogate pair a single character, it correctly reports that the string contains ten characters.
If a string contains a base character that has one or more combining characters, you can call the String.Normalize method to convert the substring to a single UTF-16 encoded code unit. The following example calls the String.Normalize method to convert the base character U+0061 (LATIN SMALL LETTER A) and combining character U+0308 (COMBINING DIAERESIS) to U+00E4 (LATIN SMALL LETTER A WITH DIAERESIS).

Thread Safety

All members of this type are thread safe. Members that appear to modify instance state actually return a new instance initialized with the new value. As with any other type, reading and writing to a shared variable that contains an instance of this type must be protected by a lock to guarantee thread safety.

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