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ASCII reserves the first 32 code points (numbers 0–31 decimal) and the last one (number 127 decimal) for control characters. These are codes intended to control peripheral devices (such as printers ), or to provide meta-information about data streams, such as those stored on magnetic tape.
Code 0 (ASCII code name NUL) is a special case. In paper tape, it is the case when there are no holes. It is convenient to treat this as a fill character with no meaning otherwise. Since the position of a NUL character has no holes punched, it can be replaced with any other character at a later time, so it was typically used to reserve space ...
It is also used as an escape sequence in some programming languages. In the ASCII character set, this character is encoded by the number 26 (1A hex). Standard keyboards transmit this code when the Ctrl and Z keys are pressed simultaneously (Ctrl+Z, often documented by convention as ^Z). [1]
Code points are commonly used in character encoding, where a code point is a numerical value that maps to a specific character.In character encoding code points usually represent a single grapheme—usually a letter, digit, punctuation mark, or whitespace—but sometimes represent symbols, control characters, or formatting. [4]
Accordingly, character sets are very often indicated by their IBM code page number. In ASCII-compatible code pages, the lower 128 characters maintained their standard ASCII values, and different pages (or sets of characters) could be made available in the upper 128 characters.
A numeric character reference refers to a character by its Universal Character Set/Unicode code point, and a character entity reference refers to a character by a predefined name. A numeric character reference uses the format &#nnnn; or &#xhhhh; where nnnn is the code point in decimal form, and hhhh is the code point in hexadecimal form.
It is also used by Mach-O to identify Universal object files, and by the Java programming language to identify Java bytecode class files. It was originally created by NeXTSTEP developers as a reference to the baristas at Peet's Coffee & Tea. [4] 0xCAFED00D: 3405697037 ("cafe dude") is used by Java as a magic number for their pack200 compression ...
This is simply the ASCII character codes from 32 to 95 coded as 0 to 63 by subtracting 32 (i.e., columns 2, 3, 4, and 5 of the ASCII table (16 characters to a column), shifted to columns 0 through 3, by subtracting 2 from the high bits); it includes the space, punctuation characters, numbers, and capital letters, but no control characters.