Control character: Difference between revisions

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In [[computing]] and [[telecommunications]], a '''control character''' or '''non-printing character''' ('''NPC''') is a [[code point]] in a [[character encoding|character set]] that does not represent a written [[Character (computing)|character]] or symbol. They are used as [[in-band signaling]] to cause effects other than the addition of a symbol to the text. All other characters are mainly ''[[graphic character]]s'', also known as ''printing characters'' (or ''printable characters''), except perhaps for "[[space (punctuation)|space]]" characters. In the [[ASCII]] standard there are 33 control characters, such as code 7, {{tt|BEL}}, which ~~rings~~ a ~~terminal~~ bell.

In [[computing]] and [[telecommunications]], a '''control character''' or '''non-printing character''' ('''NPC''') is a [[code point]] in a [[character encoding|character set]] that does not represent a written [[Character (computing)|character]] or symbol. They are used as [[in-band signaling]] to cause effects other than the addition of a symbol to the text. All other characters are mainly ''[[graphic character]]s'', also known as ''printing characters'' (or ''printable characters''), except perhaps for "[[space (punctuation)|space]]" characters. In the [[ASCII]] standard there are 33 control characters,<ref>{{cite book |at=4. Specification of the Coded Character Set |url=https://www.unicode.org/L2/L2006/06388-review-incits4.pdf |title=American National Standard for Information Systems — Coded Character Sets — 7-Bit American National Standard Code for Information Interchange (7-Bit ASCII), ANSI INCITS 4-1986 (R2002) (formerly ANSI X3.4-1986 (R1997)). |publisher=[[American National Standards Institute]], [[International Committee for Information Technology Standards]] |date=1986-03-26}}</ref> such as code 7, {{tt|BEL}}, which might [[Bell character|ring a bell]].

==History==

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| title = Component Description: IBM 2780 Data Transmission Terminal

| id = GA27-3005-3

| section = EOT (End of ~~ransmission~~)

| section = EOT (End of transmission)

| section-url = http://bitsavers.org/pdf/ibm/2780/GA27-3005-3-2780_Data_Terminal_Description_Aug71.pdf#page=31

| page = 31

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* 0x0D ([[carriage return]], {{tt|CR}}, {{tt|\r}}, {{tt|^M}}), moves the printing position to the start of the line, allowing overprinting. Used as the end of line marker in [[Classic Mac OS]], [[OS-9]], [[FLEX (operating system)|FLEX]] (and variants). A {{tt|CR+LF}} pair is used by [[CP/M]]-80 and its derivatives including [[DOS]] and [[Windows]].

* 0x1B ([[escape character|escape]], {{tt|ESC}}, {{tt|\e}} ([[GCC (software)|GCC]] only), {{tt|^[}}). Introduces an [[escape sequence]].

* 0x1C ([[file separator]], {{tt|FS}}, {{tt|^\}}) ISO/IEC 10538 uses this as a "document terminator" code to indicate the end of text in a document.<ref name="ISO 10538">{{cite ISO standard |date=1991-09-15 |title=ISO/IEC 10538:1991 Information technology — Control functions for text communication |csnumber=18608 |access-date=2026-04-04}}</ref>{{rp|page=12}}

* 0x1D ([[group separator]], {{tt|GS}}, {{tt|^]}}) ISO/IEC 10538 uses this as a "page terminator" code to indicate the end of text on a page.<ref name="ISO 10538" />{{rp|page=16}}

Control characters may do something when the user inputs them, such as Ctrl+C ([[End-of-Text character]], ETX) to interrupt the running process, and Ctrl+Z ([[Substitute character]], SUB) for ending typed-in file on Windows. These uses usually have little to do with their ASCII definition. Modern systems often describe shortcuts as though they are control characters ("type a Ctrl+V to paste") but the code number is not even used to implement this.

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==Display==

There are a number of techniques to display non-printing characters, which may be illustrated with the [[bell character]] in [[ASCII]] encoding:

* [[Code point]]: decimal 7, hexadecimal 0x07

* [[Caret notation]] in ASCII using the ''n''th letter of the alphabet: {{tt|^G}}

* An abbreviation, often three capital letters: BEL

* A special character condensing the abbreviation: Unicode U+2407 (␇), "symbol for bell"

* An [[ISO 2047]] graphical representation: Unicode U+237E (⍾), "graphic for bell"

* [[Caret notation]] in ASCII~~, where code point 00xxxxx is represented as a caret followed by~~ the ~~capital~~ letter ~~at code point 10xxxxx~~: ^G

* An [[escape sequence]], as in [[C (programming language)|C]]/[[C++]] character string codes: {{mono|\a}}, {{mono|\007}}, {{mono|\x07}}, etc.

* An abbreviation, often three capital letters: {{tt|BEL}}

* A Unicode character from the [[Control Pictures]] Unicode block that condenses the abbreviation: {{unichar|2407}}

* An [[ISO 2047]] graphical representation: {{unichar|237E}}

==How control characters map to keyboards==

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Many keyboards include keys that do not correspond to any ASCII printable or control character, for example cursor control arrows and [[word processing]] functions. The associated keypresses are communicated to computer programs by one of four methods: appropriating otherwise unused control characters; using some encoding other than ASCII; using multi-character control sequences; or using an additional mechanism outside of generating characters. "Dumb" [[computer terminal]]s typically use control sequences. Keyboards attached to stand-alone [[personal computer]]s made in the 1980s typically use one (or both) of the first two methods. Modern computer keyboards generate [[scancode]]s that identify the specific physical keys that are pressed; computer software then determines how to handle the keys that are pressed, including any of the four methods described above.

==~~The design~~ purpose==

==Design purpose==

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==See also==

* {{Slink|Arrow keys|HJKL keys}}, HJKL as arrow keys, used on ADM-3A terminal

*{{Slink|Arrow keys|HJKL keys}}, HJKL as arrow keys, used on ADM-3A terminal

* [[C0 and C1 control codes]]

*{{anl|C0 and C1 control codes}}

* [[Escape sequence]]

*{{anl|Escape sequence}}

* [[In-band signaling]]

*{{anl|Implicit directional marks}}

* [[Whitespace character]]

*{{anl|In-band signaling}}

*{{anl|Whitespace character}}

==Notes and references==

@@ Line 4: / Line 4: @@
 {{More citations needed|date=September 2007}}
-In [[computing]] and [[telecommunications]], a '''control character''' or '''non-printing character''' ('''NPC''') is a [[code point]] in a [[character encoding|character set]] that does not represent a written [[Character (computing)|character]] or symbol. They are used as [[in-band signaling]] to cause effects other than the addition of a symbol to the text. All other characters are mainly ''[[graphic character]]s'', also known as ''printing characters'' (or ''printable characters''), except perhaps for "[[space (punctuation)|space]]" characters. In the [[ASCII]] standard there are 33 control characters, such as code 7, {{tt|BEL}}, which rings a terminal bell.
+In [[computing]] and [[telecommunications]], a '''control character''' or '''non-printing character''' ('''NPC''') is a [[code point]] in a [[character encoding|character set]] that does not represent a written [[Character (computing)|character]] or symbol. They are used as [[in-band signaling]] to cause effects other than the addition of a symbol to the text. All other characters are mainly ''[[graphic character]]s'', also known as ''printing characters'' (or ''printable characters''), except perhaps for "[[space (punctuation)|space]]" characters. In the [[ASCII]] standard there are 33 control characters,<ref>{{cite book |at=4. Specification of the Coded Character Set |url=https://www.unicode.org/L2/L2006/06388-review-incits4.pdf |title=American National Standard for Information Systems — Coded Character Sets — 7-Bit American National Standard Code for Information Interchange (7-Bit ASCII), ANSI INCITS 4-1986 (R2002) (formerly ANSI X3.4-1986 (R1997)). |publisher=[[American National Standards Institute]], [[International Committee for Information Technology Standards]] |date=1986-03-26}}</ref> such as code 7, {{tt|BEL}}, which might [[Bell character|ring a bell]].
 ==History==
@@ Line 33: / Line 33: @@
   | title       = Component Description: IBM 2780 Data Transmission Terminal
   | id          = GA27-3005-3
-  | section     = EOT (End of ransmission)
+  | section     = EOT (End of transmission)
   | section-url = http://bitsavers.org/pdf/ibm/2780/GA27-3005-3-2780_Data_Terminal_Description_Aug71.pdf#page=31
   | page        = 31
@@ Line 50: / Line 50: @@
 * 0x0D ([[carriage return]], {{tt|CR}}, {{tt|\r}}, {{tt|^M}}), moves the printing position to the start of the line, allowing overprinting. Used as the end of line marker in [[Classic Mac OS]], [[OS-9]], [[FLEX (operating system)|FLEX]] (and variants). A {{tt|CR+LF}} pair is used by [[CP/M]]-80 and its derivatives including [[DOS]] and [[Windows]].
 * 0x1B ([[escape character|escape]], {{tt|ESC}}, {{tt|\e}} ([[GCC (software)|GCC]] only), {{tt|^[}}). Introduces an [[escape sequence]].
+* 0x1C ([[file separator]], {{tt|FS}}, {{tt|^\}}) ISO/IEC 10538 uses this as a "document terminator" code to indicate the end of text in a document.<ref name="ISO 10538">{{cite ISO standard |date=1991-09-15 |title=ISO/IEC 10538:1991 Information technology — Control functions for text communication |csnumber=18608 |access-date=2026-04-04}}</ref>{{rp|page=12}}
+* 0x1D ([[group separator]], {{tt|GS}}, {{tt|^]}}) ISO/IEC 10538 uses this as a "page terminator" code to indicate the end of text on a page.<ref name="ISO 10538" />{{rp|page=16}}
 Control characters may do something when the user inputs them, such as Ctrl+C ([[End-of-Text character]], ETX) to interrupt the running process, and Ctrl+Z ([[Substitute character]], SUB) for ending typed-in file on Windows. These uses usually have little to do with their ASCII definition. Modern systems often describe shortcuts as though they are control characters ("type a Ctrl+V to paste") but the code number is not even used to implement this.
@@ Line 62: / Line 64: @@
 ==Display==
 There are a number of techniques to display non-printing characters, which may be illustrated with the [[bell character]] in [[ASCII]] encoding:
-* [[Code point]]: decimal 7, hexadecimal 0x07
+* [[Caret notation]] in ASCII using the ''n''th letter of the alphabet: {{tt|^G}}
-* An abbreviation, often three capital letters: BEL
-* A special character condensing the abbreviation: Unicode U+2407 (␇), "symbol for bell"
-* An [[ISO 2047]] graphical representation: Unicode U+237E (⍾), "graphic for bell"
-* [[Caret notation]] in ASCII, where code point 00xxxxx is represented as a caret followed by the capital letter at code point 10xxxxx: ^G
 * An [[escape sequence]], as in [[C (programming language)|C]]/[[C++]] character string codes: {{mono|\a}}, {{mono|\007}}, {{mono|\x07}}, etc.
+* An abbreviation, often three capital letters: {{tt|BEL}}
+* A Unicode character from the [[Control Pictures]] Unicode block that condenses the abbreviation: {{unichar|2407}}
+* An [[ISO 2047]] graphical representation: {{unichar|237E}}
 ==How control characters map to keyboards==
@@ Line 80: / Line 81: @@
 Many keyboards include keys that do not correspond to any ASCII printable or control character, for example cursor control arrows and [[word processing]] functions.  The associated keypresses are communicated to computer programs by one of four methods: appropriating otherwise unused control characters; using some encoding other than ASCII; using multi-character control sequences; or using an additional mechanism outside of generating characters. "Dumb" [[computer terminal]]s typically use control sequences.  Keyboards attached to stand-alone [[personal computer]]s made in the 1980s typically use one (or both) of the first two methods.  Modern computer keyboards generate [[scancode]]s that identify the specific physical keys that are pressed; computer software then determines how to handle the keys that are pressed, including any of the four methods described above.
-==The design purpose==
+==Design purpose==
 {{Unreferenced section|date=February 2012}}
@@ Line 134: / Line 135: @@
 ==See also==
-* {{Slink|Arrow keys|HJKL keys}}, HJKL as arrow keys, used on ADM-3A terminal
+*{{Slink|Arrow keys|HJKL keys}}, HJKL as arrow keys, used on ADM-3A terminal
-* [[C0 and C1 control codes]]
+*{{anl|C0 and C1 control codes}}
-* [[Escape sequence]]
+*{{anl|Escape sequence}}
-* [[In-band signaling]]
+*{{anl|Implicit directional marks}}
-* [[Whitespace character]]
+*{{anl|In-band signaling}}
+*{{anl|Whitespace character}}
 ==Notes and references==

Control character: Difference between revisions

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