Appendix:Control characters

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Besides alphabetic characters and symbols, Unicode also includes a variety of control characters with no graphical representation. While some of these are actually used to modify certain characters, others are little more than remnants from older times.

C0 (ASCII and derivatives)Edit

C0 control codes are in the Unicode range U+0000-U+001F, and were inherited from the ASCII standard. Often, these cannot be input directly because they fulfill specific low-level functions in the operating system.

Seq Dec Hex Acro Name C Description
^@ 00 00 NUL Null \0 Originally used to allow gaps to be left on paper tape for edits. Later used for padding after a code that might take a terminal some time to process (e.g. a carriage return or line feed on a printing terminal). Now often used as a string terminator, especially in the C programming language.
^A 01 01 SOH Start of Heading First character of a message header.
^B 02 02 STX Start of text First character of message text, and may be used to terminate the message heading.
^C 03 03 ETX End of Text Often used as a "break" character (Ctrl-C) to interrupt or terminate a program or process.
^D 04 04 EOT End of Transmission Used on Unix to signal end-of-file condition on, or to logout from a terminal.
^E 05 05 ENQ Enquiry Signal intended to trigger a response at the receiving end, to see if it is still present.
^F 06 06 ACK Acknowledge Response to an ENQ, or an indication of successful receipt of a message.
^G 07 07 BEL Bell \a Originally used to sound a bell on the terminal. Later used for a beep on systems that didn't have a physical bell. May also quickly turn on and off inverse video (a visual bell).
^H 08 08 BS Backspace \b Move the cursor one position leftwards. On input, this may delete the character to the left of the cursor. On output, where in early computer technology a character once printed could not be erased, the backspace was sometimes used to generate accented characters in ASCII. For example, à could be produced using the three character sequence a BS ` (0x61 0x08 0x60). This usage is now deprecated and generally not supported. To provide disambiguation between the two potential uses of backspace, the cancel character control code was made part of the standard C1 control set.
^I 09 09 HT Character Tabulation, Horizontal Tabulation \t Position to the next character tab stop.
^J 10 0A LF Line Feed \n On typewriters, printers, and some terminal emulators, moves the cursor down one row without affecting its column position. On Unix, used to mark end-of-line. In MS-DOS, Windows, and various network standards, LF is used following CR as part of the end-of-line mark.
^K 11 0B VT Line Tabulation, Vertical Tabulation \v Position the form at the next line tab stop.
^L 12 0C FF Form Feed \f On printers, load the next page. Treated as whitespace in many programming languages, and may be used to separate logical divisions in code. In some terminal emulators, it clears the screen.
^M 13 0D CR Carriage Return \r Originally used to move the cursor to column zero while staying on the same line. On Mac OS (pre-Mac OS X), as well as in earlier systems such as the Apple II and Commodore 64, used to mark end-of-line. In MS-DOS, Windows, and various network standards, it is used preceding LF as part of the end-of-line mark. The Enter or Return key on a keyboard will send this character, but it may be converted to a different end-of-line sequence by a terminal program.
^N 14 0E SO Shift Out Switch to an alternate character set.
^O 15 0F SI Shift In Return to regular character set after Shift Out.
^P 16 10 DLE Data Link Escape Cause the following octets to be interpreted as raw data, not as control codes or graphic characters. Returning to normal usage would be implementation-dependent.
^Q 17 11 DC1 Device Control One (XON) These four control codes are reserved for device control, with the interpretation dependent upon the device they were connected. DC1 and DC2 were intended primarily to indicate activating a device while DC3 and DC4 were intended primarily to indicate pausing or turning off a device. In actual practice DC1 and DC3 (known also as XON and XOFF respectively in this usage) quickly became the de facto standard for software flow control.
^R 18 12 DC2 Device Control Two
^S 19 13 DC3 Device Control Three (XOFF)
^T 20 14 DC4 Device Control Four
^U 21 15 NAK Negative Acknowledge Sent by a station as a negative response to the station with which the connection has been set up. In binary synchronous communication protocol, the NAK is used to indicate that an error was detected in the previously received block and that the receiver is ready to accept retransmission of that block. In multipoint systems, the NAK is used as the not-ready reply to a poll.
^V 22 16 SYN Synchronous Idle Used in synchronous transmission systems to provide a signal from which synchronous correction may be achieved between data terminal equipment, particularly when no other character is being transmitted.
^W 23 17 ETB End of Transmission Block Indicates the end of a transmission block of data when data are divided into such blocks for transmission purposes.
^X 24 18 CAN Cancel Indicates that the data preceding it are in error or are to be disregarded.
^Y 25 19 EM End of medium Intended as means of indicating on paper or magnetic tapes that the end of the usable portion of the tape had been reached.
^Z 26 1A SUB Substitute Originally intended for use as a transmission control character to indicate that garbled or invalid characters had been received. It has often been put to use for other purposes when the in-band signaling of errors it provides is unneeded, especially where robust methods of error detection and correction are used, or where errors are expected to be rare enough to make using the character for other purposes advisable.
^[ 27 1B ESC Escape The Esc key on the keyboard will cause this character to be sent on most systems. It can be used in software user interfaces to exit from a screen, menu, or mode, or in device-control protocols (e.g., printers and terminals) to signal that what follows is a special command sequence rather than normal text. In systems based on ISO/IEC 2022, even if another set of C0 control codes are used, this octet is required to always represent the escape character.
^\ 28 1C FS File Separator Can be used as delimiters to mark fields of data structures. If used for hierarchical levels, US is the lowest level (dividing plain-text data items), while RS, GS, and FS are of increasing level to divide groups made up of items of the level beneath it.
^] 29 1D GS Group separator
^^ 30 1E RS Record Separator
^_ 31 1F US Unit separator
While not technically part of the C0 control character range, the following two characters are defined in ISO/IEC 2022 as always being available regardless of which sets of control characters and graphics characters have been registered. They can be thought of as having some characteristics of control characters.
  32 20 SP Space Space is a graphic character. It has a visual representation consisting of the absence of a graphic symbol. It causes the active position to be advanced by one character position. In some applications, Space can be considered a lowest-level "word separator" to be used with the adjacent separator characters.
^? 127 7F DEL Delete Not technically part of the C0 control character range, this was originally used to mark deleted characters on paper tape, since any character could be changed to all ones by punching holes everywhere. On VT100 compatible terminals, this is the character generated by the key labelled , usually called backspace on modern machines, and does not correspond to the PC delete key.

C1 setEdit

C1 control codes are in the Unicode range U+0080-U+009F, and were inherited from the ISO 8859 series of standards. Nowadays, these control codes are rarely if ever used for their intended purpose, and often their presence in the text indicates an ill-formatted alternate character set, such as Windows-1252.

Esc+ Dec Hex Acro Name Description
@ 128 80 PAD Padding Character Listed as XXX in Unicode. Not part of ISO/IEC 6429 (ECMA-48).
A 129 81 HOP High Octet Preset
B 130 82 BPH Break Permitted Here Follows a graphic character where a line break is permitted. Roughly equivalent to a soft hyphen except that the means for indicating a line break is not necessarily a hyphen. Not part of the first edition of ISO/IEC 6429.
C 131 83 NBH No Break Here Follows the graphic character that is not to be broken. Not part of the first edition of ISO/IEC 6429.
D 132 84 IND Index Move the active position one line down, to eliminate ambiguity about the meaning of LF. Deprecated in 1988 and withdrawn in 1992 from ISO/IEC 6429 (1986 and 1991 respectively for ECMA-48).
E 133 85 NEL Next Line Equivalent to CR+LF. Used to mark end-of-line on some IBM mainframes.
F 134 86 SSA Start of Selected Area Used by block-oriented terminals.
G 135 87 ESA End of Selected Area
H 136 88 HTS Character Tabulation Set
Horizontal Tabulation Set
Causes a character tabulation stop to be set at the active position.
I 137 89 HTJ Character Tabulation With Justification
Horizontal Tabulation With Justification
Similar to Character Tabulation, except that instead of spaces or lines being placed after the preceding characters until the next tab stop is reached, the spaces or lines are placed preceding the active field so that preceding graphic character is placed just before the next tab stop.
J 138 8A VTS Line Tabulation Set
Vertical Tabulation Set
Causes a line tabulation stop to be set at the active position.
K 139 8B PLD Partial Line Forward
Partial Line Down
Used to produce subscripts and superscripts in ISO/IEC 6429, e.g., in a printer.
Subscripts use PLD text PLU while superscripts use PLU text PLD..
L 140 8C PLU Partial Line Backward
Partial Line Up
M 141 8D RI Reverse Line Feed
Reverse Index
N 142 8E SS2 Single-Shift 2 Next character invokes a graphic character from the G2 or G3 graphic sets respectively. In systems that conform to ISO/IEC 4873 (ECMA-43), even if a C1 set other than the default is used, these two octets may only be used for this purpose.
O 143 8F SS3 Single-Shift 3
P 144 90 DCS Device Control String Followed by a string of printable characters (0x20 through 0x7E) and format effectors (0x08 through 0x0D), terminated by ST (0x9C).
Q 145 91 PU1 Private Use 1 Reserved for a function without standardized meaning for private use as required, subject to the prior agreement of the sender and the recipient of the data.
R 146 92 PU2 Private Use 2
S 147 93 STS Set Transmit State
T 148 94 CCH Cancel character Destructive backspace, intended to eliminate ambiguity about meaning of BS.
U 149 95 MW Message Waiting
V 150 96 SPA Start of Protected Area Used by block-oriented terminals.
W 151 97 EPA End of Protected Area
X 152 98 SOS Start of String Followed by a control string terminated by ST (0x9C) that may contain any character except SOS or ST. Not part of the first edition of ISO/IEC 6429.
Y 153 99 SGCI Single Graphic Character Introducer Listed as XXX in Unicode. Not part of ISO/IEC 6429.
Z 154 9A SCI Single Character Introducer To be followed by a single printable character (0x20 through 0x7E) or format effector (0x08 through 0x0D). The intent was to provide a means by which a control function or a graphic character that would be available regardless of which graphic or control sets were in use could be defined. Definitions of what the following byte would invoke was never implemented in an international standard. Not part of the first edition of ISO/IEC 6429.
[ 155 9B CSI Control Sequence Introducer Used to introduce control sequences that take parameters.
\ 156 9C ST String Terminator
] 157 9D OSC Operating System Command Followed by a string of printable characters (0x20 through 0x7E) and format effectors (0x08 through 0x0D), terminated by ST (0x9C). These three control codes were intended for use to allow in-band signaling of protocol information, but are rarely used for that purpose.
^ 158 9E PM Privacy Message
_ 159 9F APC Application Program Command

Unicode control charactersEdit

Unicode control characters are control characters which do not occur in the C0 or C1 sets. While the C0 and C1 control characters are of the type Cc (Other, Control), control characters exclusive to Unicode are in the category Cf (Other, Format).

Dec Hex Acro Name Description
173 AD SHY Soft Hyphen This character allows line breaking of words at specific points, and if a word is broken up like this this character will show up as a hyphen.
847 34F CGJ Combining Grapheme Joiner Separates diacriticial marks. Can sometimes act as a variation selector (for example, to differentiate between the dieresis and umlaut usages of ¨).
1807 70F SAM Syriac Abbreviation Mark In Syriac script, this marks the beginning of an abbreviation. This control character is rendered as a line at the top with dots at each end as well as in the middle which continues until the end of the word. It is used to mark contractions as well as Syriac numerals.
6158 180E MVS Mongolian Vowel Separator Used orthographically in Mongolian script.
8203 200B ZWSP Zero-Width Space Used to allow line breaking for scripts which traditionally do not use spaces, like Thai. This character is always invisible.
8204 200C ZWNJ Zero-Width Non-Joiner Specifically prevents joining of characters, especially in cursive scripts auch as Arabic. This character is needed for correct notation of some languages, most notably Persian. When used in Indic scripts, it specifically enforces the halant form.
8205 200D ZWJ Zero-Width Joiner Specifically enforces joining of characters, especially in cursive scripts auch as Arabic. This is used, for example, to display Arabic characters standalone in various positions. When used in Indic scripts, it specifically enforces the half form.
8206 200E LRM Left-to-Right Mark Specifies the writing direction in bidirectional text.
8207 200F RLM Right-to-Left Mark
8234 202A LRE Left-to-Right Embedding Used to embed a text in a specific writing direction. Used specifically where the writing direction of the surrounding environment is not known.
8235 202B RLE Right-to-Left Embedding
8236 202C PDF Pop Directional Formatting Acts as a closing tag for LRE, RLE, LRO and RLO, restoring the writing direction to its previous state.
8237 202D LRO Left-to-Right Override Forces a text to be written in a specific writing direction, even if the writing system would normally not be written in this direction.
8238 202E RLO Right-to-Left Override
8288 2060 WJ Word Joiner Used specifically as a zero-width non-breaking space, to disambiguate from the use of ZWNBSP as a byte order mark.
8289 2061 FA Function Application
8290 2062 IT Invisible Times In mathematical formulae, indicates an implied multiplication operator, for use by automated programs.
8291 2063 IS Invisible Separator
8292 2064 IP Invisible Plus In mathematical formulae, indicates an implied addition operator, for use by automated programs.
8298 206A ISS Inhibit Symmetric Swapping Enables or disables the mirroring of specific glyphs, such as the parentheses, in a bidirectional context. Deprecated.
8299 206B ASS Activate Symmetric Swapping
8300 206C IAFS Inhibit Arabic Form Shaping Enables or disables the shaping of Arabic Presentation Forms. Deprecated.
8301 206D AAFS Activate Arabic Form Shaping
8302 206E NADS National Digit Shapes Replaces the Arabic digits (123) with Arabic-Indic digits (١٢٣). Deprecated.
8303 206F NODS Nominal Digit Shapes
65279 FEFF ZWNBSP Zero-Width Non-Breaking Space This character is nowadays used as a Byte Order Mark (BOM), to allow programs to detect whether a given UTF-16 or UTF-32 text is formatted in big-endian or little-endian. Its use as a zero-width non-breaking space is now deprecated - the WJ control character should be used for this purpose.
65529 FFF9 IAA Interlinear Annotation Anchor These characters are intended to be used to add annotations to words, as in, for example, Japanese furigana. The first character, IAA, is to be added at the beginning of the word to be annotated. The IAS character marks the start of the annotation, and the IAT character ends the annotation. Note however that most implementations do not support these control characters.
65530 FFFA IAS Interlinear Annotation Separator
65531 FFFB IAT Interlinear Annotation Terminator

Language tagsEdit

Language tags are encoded in the Unicode range U+E0000-U+E007F. These were added as a way to represent the language of a text without having to resort to higher-level mechanisms. They were intended specifically for Chinese, to allow a text to unambiguously represent the simplified or traditional form of a Chinese character. However, these characters haven't caught on, and their use is now deprecated by Unicode.

Example:

Literal input Unicode character codes Displayed output
次󠀁󠁺󠁨󠀭󠁈󠁡󠁮󠁴次󠁿次 6B21 E0001 E007A E0068 E002D E0048 E0061 E006E E0074 6B21 E007F 6B21

Variation selectorsEdit

Variation selectors are encoded in several Unicode ranges scattered across. Their purpose is to mark variations of a character in certain cases where it may be appropriate to specify one form of a character. The variations are not arbitrary, but specifically listed in the Unicode standard. There are currently four main uses of variation selectors:

  • Variation selectors 1-16 are encoded in the U+FE00-U+FE0F block. Only the first one is ever actually used in Unicode, and it specifies common variants of some mathematical symbols, however these variants are ill-defined, and few implementations support these.
  • The same variation selector is also used orthographically in the Phags-pa script.
  • Variation selectors 17-256 are encoded in the U+E0100-U+E01EF block. This set is intended to define special variants of Han ideographs.
  • The Mongolian block has its own set of variation selectors which is used orthographically in this script.

See alsoEdit

Last modified on 20 July 2013, at 00:08