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33.6 Character Sets

An Emacs character set, or charset, is a set of characters in which each character is assigned a numeric code point. (The Unicode Standard calls this a coded character set.) Each Emacs charset has a name which is a symbol. A single character can belong to any number of different character sets, but it will generally have a different code point in each charset. Examples of character sets include ascii, iso-8859-1, greek-iso8859-7, and windows-1255. The code point assigned to a character in a charset is usually different from its code point used in Emacs buffers and strings.

Emacs defines several special character sets. The character set unicode includes all the characters whose Emacs code points are in the range 0..#x10FFFF. The character set emacs includes all ASCII and non-ASCII characters. Finally, the eight-bit charset includes the 8-bit raw bytes; Emacs uses it to represent raw bytes encountered in text.

— Function: charsetp object

Returns t if object is a symbol that names a character set, nil otherwise.

— Variable: charset-list

The value is a list of all defined character set names.

— Function: charset-priority-list &optional highestp

This function returns a list of all defined character sets ordered by their priority. If highestp is non-nil, the function returns a single character set of the highest priority.

— Function: set-charset-priority &rest charsets

This function makes charsets the highest priority character sets.

— Function: char-charset character &optional restriction

This function returns the name of the character set of highest priority that character belongs to. ASCII characters are an exception: for them, this function always returns ascii.

If restriction is non-nil, it should be a list of charsets to search. Alternatively, it can be a coding system, in which case the returned charset must be supported by that coding system (see Coding Systems).

— Function: charset-plist charset

This function returns the property list of the character set charset. Although charset is a symbol, this is not the same as the property list of that symbol. Charset properties include important information about the charset, such as its documentation string, short name, etc.

— Function: put-charset-property charset propname value

This function sets the propname property of charset to the given value.

— Function: get-charset-property charset propname

This function returns the value of charsets property propname.

— Command: list-charset-chars charset

This command displays a list of characters in the character set charset.

Emacs can convert between its internal representation of a character and the character's codepoint in a specific charset. The following two functions support these conversions.

— Function: decode-char charset code-point

This function decodes a character that is assigned a code-point in charset, to the corresponding Emacs character, and returns it. If charset doesn't contain a character of that code point, the value is nil. If code-point doesn't fit in a Lisp integer (see most-positive-fixnum), it can be specified as a cons cell (high . low), where low are the lower 16 bits of the value and high are the high 16 bits.

— Function: encode-char char charset

This function returns the code point assigned to the character char in charset. If the result does not fit in a Lisp integer, it is returned as a cons cell (high . low) that fits the second argument of decode-char above. If charset doesn't have a codepoint for char, the value is nil.

The following function comes in handy for applying a certain function to all or part of the characters in a charset:

— Function: map-charset-chars function charset &optional arg from-code to-code

Call function for characters in charset. function is called with two arguments. The first one is a cons cell (from . to), where from and to indicate a range of characters contained in charset. The second argument passed to function is arg.

By default, the range of codepoints passed to function includes all the characters in charset, but optional arguments from-code and to-code limit that to the range of characters between these two codepoints of charset. If either of them is nil, it defaults to the first or last codepoint of charset, respectively.