character encoding

A character encoding consists of a code that pairs a sequence of characters from a given character set (sometimes referred to as code page) with something else, such as a sequence of natural numbers, octets or electrical pulses, in order to facilitate the storage of text in computers and the transmission of text through telecommunication networks. Common examples include Morse code, which encodes letters of the Latin alphabet as series of long and short depressions of a telegraph key; and ASCII, which encodes letters, numerals, and other symbols, both as integers and as 7-bit binary versions of those integers, generally extended with an extra zero-bit to facilitate storage in 8-bit bytes (octets).
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<character> (Or "character encoding scheme") A mapping of binary values to code positions and back; generally a 1:1 (bijective) mapping.
In the case of ASCII, this is generally a f(x)=x mapping: code point 65 maps to the byte value 65, and vice versa. This is possible because ASCII uses only code positions representable as single bytes, i.e., values between 0 and 255, at most. (US-ASCII only uses values 0 to 127, in fact.)
Unicode and many CJK coded character sets use many more than 255 positions, requiring more complex mappings: sometimes the characters are mapped onto pairs of bytes (see DBCS). In many cases, this breaks programs that assume a one-to-one mapping of bytes to characters, and so, for example, treat any occurrance of the byte value 13 as a carriage return. To avoid this problem, character encodings such as UTF-8 were devised.
(1998-10-18)