控制字符不表示可打印的字符尚未而是用来启动特定的动作字符。相反,控制字符用于执行任何操作,以在显示器上打印可打印字符。它们还用作带内信令,以引起影响,而不是将符号扩展到内容。
另一方面,可打印字符用于在屏幕上显示字符,例如字母,符号,数字和字母数字字符。有不同类型的控制字符,包括打印控制字符,数据结构控制字符和传输控制字符。条形码和RFID扫描仪的前缀或后缀部分经常使用大量此类字符。
1870年的Baudot代码中提供了一种控制字符:NUL和DEL。 1901年,Murray代码包括回车符(CR)和换行符(LF),而Baudot代码的不同变体包括其他控制字符。贝尔字符(BEL)响起了信号执行人员的声音,同样是早期的电传打字控制字符。
控制字符分为三部分0:
- ASCII控制字符–
ASCII控制字符包含代码0–31(十六进制00–1F)。此范围也称为C0集。在32和127(十六进制20和7F)处有两个额外的控件。 ASCII表号0–31指定用于控制命令某些外围设备(例如打印机)的控制字符。例如,12表示换页/新页函数。此命令指示打印机转到下一页的开头。控制字符的集合涵盖了许多应用程序。有“格式效应器”,用于规范纯内容的呈现。有用于传输协议的“传输控制”和用于启动,运行和停止辅助设备的“设备控制”。
有“信息分隔符”控制不同的信息位。存在其他控件,用于创建警告,显示文件/文本/代码/脚本的结尾以及用于处理错误。
ASCII控制字符具有多种用途,例如文本布局,通信和设备控制,但这仅仅是冰山一角。
- C1控制字符–
C1涵盖128-159(十六进制80-9F)。 C1本质上用于显示器和打印机。该集合由ANSI转义序列和VT100标识。C1套在1970年代末推出。尽管实际上控件的一部分也代表了不同的用途,但它基本上是用于控制监视器和打印机小工具的。 C1集旨在与C0集一起使用。
C1套包含“格式效果器”,可在打印时控制水平和垂直移位。有用于描述换行符或换行符的“演示控件”。有用于结构和表单填充的“区域定义”控件。
- ISO 8859独特字符–
ISO 8859是8位字符集的集合。集合包括不同的拉丁语,西里尔字母,希腊语,阿拉伯语,希伯来语和泰语字符。 ISO 8859是由Windows字符集(“ ANSI代码页”)标识的,但是它们之间确实是唯一的。ISO 8859具有两个重要字符:非中断(NBSP)和软连字符(SHY)。尽管事实上它们在ISO 8859中并不是真正的控制字符,但它们中的两个具有类似控制字符的属性。
以下是一些基本的控制代码:
Caret Notation | Hex Code | Abbreviation | Name | Description |
---|---|---|---|---|
^@ | 00 | NULL | Null | Used to perform media-fill and allow gaps. Also used for padding after any code and to mark end of string, notably in programming language C/C++. |
^A | 01 | STX | Start of Header | Used as first character of head of data broadcast/message. It is usually used as field separator in Apache Hadoop. |
^B | 02 | SOT | Start of Text | Heads text and used to mark end of heading. |
^C | 03 | ETX | End of Text |
Marks end of text. In keyboard input, it is frequently used as Break character to interrupt process. Notably seen in Unix based command lines, nano editor, etc. as (^C) to break command. |
^D | 04 | EOT | End of Transmission |
Used to mark end of transmission of one or more texts(may involve header, broadcast text, and post-text). It is also used to mark end-of-file(EOF) on terminal in UNIX based OS. |
^E | 05 | ENQ | Enquiry | Requests for reply from remote terminal, response may include transmitter identification and/or transmitter status. |
^F | 06 | ACK | Acknowledge | This character is sent by receiver as approving response to sender. (Response to ENQ) |
^G | 07 | ACK | Bell | A control character to call for attention. It may control alarm or attention devices. Initially, it was used to play bell sound on terminal. |
^H | 08 | BS | BackSpace | Shifts cursor one character position behind. While in input mode this might delete character to left of cursor. When in output mode, character once written could not be deleted(Primitively). |
^I | 09 | HT | Horizontal Tabulation | Shifts cursor to next determined character position on the same line. |
^J | 0A | LF | Line Feed | Shifts cursor to equivalent character position of next line. It is used to mark end-of-line(EOF) in UNIX. In DOS/Windows LF is used after CR(Carriage Return) to mark end-of-line. |
^K | 0B | VT | Vertical Tabulation | Shifts cursor at next line. |
^L | 0C | FF | Form Feed |
It commands printer to discard current page and to proceed to print at the next one. More so, it also acts as whitespace in various programming languages, |
^M | 0D | CR | Carriage Return | Primitively used to move cursor to very first column while staying on the same line/row. In DOS, /Windows, it is used before LF to mark end-of-line(EOF). Enter/Return key corresponds to this character. |
^N | 0E | SO | Shift Out | Switches to substitute character set. |
^O | 0F | SI | Shift In | Reverts to general character set after Shift Out. |
^P | 10 | DLE | Data Link Escape | It is used particularly to deliver additional data transmission control functions. Only graphic characters and transmission control characters can be used in DLE sequences. |
^Q | 11 | DC1 | Device Control 1 (XON) | A device control character, basically dedicated to turning on or starting essential device. It might also be used to restore any device to basic mode of operation. |
^R | 12 | DC2 | Device Control 2 | A device control character which is basically dedicated to turning on or starting essential device. It might also be used to set any device to special mode of operation |
^S | 13 | DC3 | Device Control 3 (XOFF) | A device control character which is basically dedicated to turning off or stopping an essential device. Also acts as secondary step stop(e.g: wait, pause, stand-by or halt) |
^T | 14 | DC4 | Device Control 4 | A device control character, basically dedicated to turning off al device. It might also be used for any device control purpose not granted by other DCs. |
^U | 15 | NAK | Negative acknowledge | A control character sent by receiver as negative acknowledgment/response to transmitter. NAK also indicates that an error was identified in last received block. |
^V | 16 | SYN | Synchronous Idle | Used by synchronous transmission network to provide signal from which synchronous rectification may be achieved between data terminal equipment |
^W | 17 | ETB | End of Transmission Block | marks end of transmission segment of data (where data is divided into such segments for transmission) |
^X | 18 | CAN | Cancel | Indicates that data preceding it is in error. Hence, data is to be ignored. |
^Y | 19 | EM | End of Medium | A control character that can be used to find physical end of medium or end of wanted portion of data. |
^Z | 1A | SUB | Substitute | Used as an alternative for character that has been detected to be invalid or in error. On Unix, ^Z is keyboard signal to suspend process. In DOS/Windows, it is used to mark end of file, in cmd terminal, text files and many scripts. |
^[ | 1B | ESC | Escape | Esc key corresponds to this control character on almost every operating system. Used in many interface to escape from screen, menu, or process., |
^\ | 1C | FS | File Separator | Used to separate data logically, its specific purpose has to be defined for each application. When used in hierarchical order, it delimits data item called file. |
^] | 1D | GS | Group Separator | Used to separate data logically; its specific purpose has to be defined for each application. When used in hierarchical order, it delimits data item called group. |
^^ | 1E | RS | Record Separator | Used to separate data logically; its specific purpose has to be defined for each application. When used in hierarchical order, it delimits data item called record. |
^_ | 1F | US | Unit Separator | Used to separate data logically; its specific purpose has to be defined for each application. When used in hierarchical order, it delimits data item called unit. |
20 | SP | Space | Space is graphic character. Shifts cursor to move by one character position. | |
^? | 7F | DEL | Delete | The delete control character is last character in ASCII repertoire. It was designed to erase incorrect characters. |