Elisp: Character Type

What is Char Type

In emacs lisp, characters are represented as integers of the character's code point.

• Unicode: Code Point (Char ID)

For example, the char “a” in elisp is just 97, because its code point is 97.

There is no dedicated char type

There is no actual character type in emacs lisp. Whether a integer is a character depends on programer's intention.

Readable Char Syntax

• Char can also be represented like this ?a for easy human reading.
• ?a means the character “a”.
• ?a eval to 97.

• Some characters, such as backslash, require a backslash. e.g. ?\\

You can also represent char by (string-to-char "a")

(eq 97 ?a )
;; t

(eq 97 (string-to-char "a"))
;; t

ASCII Control Chars and Backslash

Syntax of the form ?\char may have special meaning, depending what char is. They either represent a ASCII control character, or just the character char. For example, ?\n is the newline char. ?\\ is backslash char.

Here's a list of special meaning with the backslash:

〔see ASCII Characters〕

some other important special case

• SEMICOLON need backslash, else it became lisp comment. Correct syntax is ?\;
• QUOTATION MARK need backslash, else it became start of string. Correct syntax is ?\"

• CIRCUMFLEX ACCENT cannot precede with backslash because it become control char. Correct syntax is ?^

Find a Char's code point Interactively

call describe-char

• Emacs: find char name, font, position, code point, encoding, etc

Insert Char

insert-char

(insert-char CHARACTER &optional COUNT INHERIT)

insert character by its code point.

(insert-char 97 3)
;; aaa

Get Char from Buffer

char-before

(char-before &optional POS)

return the code point of character before cursor. If POS is out of range, return nil.

char-after

return the code point of character after cursor. If POS is out of range, return nil.

preceding-char

(preceding-char)

return the code point of character before cursor. If point is at the beginning of the buffer, returns 0.

following-char

(following-char)

return the code point of character after cursor. If at the end of the buffer or accessible region, return 0.

Convert Char and String

char-to-string

(char-to-string CHAR)

convert a CHAR (code point) to string of single character.

string-to-char

(string-to-char STRING)

return the first char in string. (return a integer that's the char's code point)

string

(string &rest CHARACTERS)

convert chars to string.

(string 97)
;; "a"

(string 97 98)
"ab"

Equality Test, Check is Char or String

char-equal

(char-equal C1 C2).

Return t if two characters match, but dependent on a Buffer Local Variable case-fold-search.

Case is ignored if case-fold-search is non-nil in the current buffer.

🛑 WARNING: when at beginning of buffer, char-before return nil. Using char-equal result error because argument needs to be integer. So, in general, better use eq if you don't care about letter case. 〔see Elisp: Equality Test〕

;; check if char before is a newline
(char-equal (char-before) 10)
;; depends on case-fold-search for letter characters

;; better use eq for single case characters, because char-before return nil if point is at beginning, and char-equal would error because it expect integer
(eq (char-before) 10)

char-or-string-p

check if object is char or string.

Replace Chars

• translate-region
• subst-char-in-string
• subst-char-in-region

Reference

• Character Type (ELISP Manual)