Editing Null character (section)

{{short description|Control character with value 0}}
{{Other uses|Null symbol (disambiguation){{!}}Null symbol}}
The '''null character''' is a [[control character]] with the value [[zero]].<ref>{{cite IETF
|rfc=20
|title=ASCII format for Network Interchange
|section=5.2
|quote=NUL (Null): The all-zeros character which may serve to accomplish time fill and media fill.
|publisher=[[Internet Engineering Task Force|IETF]]
}}</ref><ref>{{cite web
 |url         = http://kikaku.itscj.ipsj.or.jp/ISO-IR/001.pdf
 |title       = The set of control characters of the ISO 646
 |publisher   = Secretariat ISO/TC 97/SC 2
 |date        = 1975-12-01
 |page        = 4.4
 |quote       = Position: 0/0, Name: Null, Abbreviation: Nul
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20140512221203/http://kikaku.itscj.ipsj.or.jp/ISO-IR/001.pdf
 |archive-date = 2014-05-12
}}</ref><ref>{{cite web
 |url=https://www.fileformat.info/info/unicode/char/0000/index.htm
 |title=Unicode Character 'NULL' (U+0000)
 |access-date=2018-10-20
}}</ref><ref>{{cite web
 |url=https://www.unicode.org/charts/PDF/U0000.pdf
 |title=C0 Controls and Basic Latin 
 |date=2018
 |publisher=Unicode Consortium
 |access-date=2018-10-20}}
</ref><ref>"A byte with all bits set to 0, called the ''null character'', shall exist in the basic execution character set; it is used to terminate a character string literal." — ANSI/ISO 9899:1990 (the ANSI C standard), section 5.2.1</ref> Many [[character set]]s include a [[code point]] for a null character {{endash}} including [[Unicode]] ([[Universal Coded Character Set]]), [[ASCII]] ([[ISO/IEC 646]]), [[Baudot code|Baudot]], [[ITA2]] codes, the [[C0 and C1 control codes|C0 control code]], and [[EBCDIC]]. In modern character sets, the null character has a code point value of zero which is generally translated to a single code unit with a zero value. For instance, in [[UTF-8]], it is a single, zero byte. However, in [[UTF-8#Modified UTF-8|Modified UTF-8]] the null character is encoded as two bytes <!-- An overlong encoding of U+0000 -->: {{tt|0xC0,0x80}}. This allows the byte with the value of zero, which is not used for any character, to be used as a string terminator.

Originally, its meaning was like [[NOP (code)|NOP]] {{endash}} when sent to a [[computer printer|printer]] or a [[computer terminal|terminal]], it had no effect (although some terminals incorrectly displayed it as [[space (punctuation)|space]]). When electromechanical [[teleprinter]]s were used as computer output devices, one or more null characters were sent at the end of each printed line to allow time for the mechanism to return to the first printing position on the next line.{{Citation needed|date=April 2010}} On [[punched tape]], the character is represented with no holes at all, so a new unpunched tape is initially filled with null characters, and often text could be inserted at a reserved space of null characters by punching the new characters into the tape over the nulls.

A [[null-terminated string]] is a commonly used data structure in the [[C (programming language)|C programming language]], its many derivative languages and other programming contexts that uses a null character to indicate the end of a [[string (computer science)|string]].<ref>"A ''string'' is a contiguous sequence of characters terminated by and including the first null character" — ANSI/ISO 9899:1990 (the ANSI C standard), section 7.1.1</ref><ref>{{citation |title=Working Draft, Standard for Programming Language C++ |type=ISO 14882 standard working draft |date=28 February 2011 |publisher=[[International Organization for Standardization|ISO]]/[[International Electrotechnical Commission|IEC]] |page=427 |url=http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3242.pdf |access-date=27 February 2013 |id=N3242=11-0012 |quote=A ''null-terminated byte string'', or NTBS, is a character sequence whose highest-addressed element with defined content has the value zero (the ''terminating null character''); no other element in the sequence has the value zero.}}</ref> This design allows a string to be any length at the cost of only one extra character of memory. The common competing design for a string stores the length of the string as an [[integer]] [[data type]], but this limits the size of the string to the range of the integer (for example, 255 for a byte).

For [[byte]] storage, the null character can be called a '''null byte'''.