character encoding

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)