Elisp: Character Type

What is Char Type

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

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

No Actual 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 Codepoint Interactively

use describe-char

• Emacs: Get Char Info. Name, Position, Font, Encoding, Syntax, Etc

Get Char from Buffer

char-before

return the codepoint of character before cursor.

char-after

return the codepoint of character after cursor.

Convert Char and String

char-to-string

(char-to-string CHAR)

convert a CHAR (codepoint) 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 codepoint)

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)