Unicode control characters: Difference between revisions

Revision as of 11:06, 8 February 2022

Revision as of 20:55, 8 February 2022

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{{short description|Non-printing format effectors and control codes included in Unicode}}

Many [[Unicode]] characters are used to control the interpretation or display of text, but these characters themselves have no visual or spatial representation. For example, the [[null character]] ({{unichartt|U+0000|NULL|nlink}}&nbsp;<span style="font-size:85%;">[[control characters}}|NULL]]</span>) is used in C-programming application environments to indicate the end of a string of characters. In this way, these programs only require a single starting memory address for a [[String (computer science)|string]] (as opposed to a starting address and a length), since the string ends once the program reads the null character.

In the narrowest sense, a ''control code'' is a character with the [[Unicode character property#General Category|general category]] {{code|Cc}}, which comprises the [[C0 and C1 control codes]], a concept defined in [[ISO/IEC 2022]] and inherited by Unicode, with the most common set being defined in [[ISO/IEC 6429]]. Control codes are handled distinctly from ordinary Unicode characters, for example, by not being assigned character names (although they are assigned normative formal aliases).<ref name="aliases">{{cite web |url=https://www.unicode.org/Public/UCD/latest/ucd/NameAliases.txt |title=Name Aliases |work=Unicode Character Database |institution=[[Unicode Consortium]]}}</ref> In a broader sense, other non-printing format characters, such as those used in [[bidirectional text]], are also referred to as ''control characters'' by software;<ref name="segan">{{cite web |url=http://kvota.net/guadec/localised-desktop-talk/ |title=Towards a localised desktop |quotation=For some cases where automatic decision making doesn't work, you can manually add specific direction markers by right-clicking the text field, choosing "Insert Unicode control character" from the menu, and selecting appropriate direction mark. This would allow you, for instance, to start your RTL text with an otherwise LTR word (such as "GNOME"). |first=Danilo |last=Segan}}</ref> these are mostly assigned to the general category {{code|Cf}} (format), used for format effectors introduced and defined by Unicode itself.