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33.5 Character Codes

The unibyte and multibyte text representations use different character codes. The valid character codes for unibyte representation range from 0 to #xFF (255)—the values that can fit in one byte. The valid character codes for multibyte representation range from 0 to #x3FFFFF. In this code space, values 0 through #x7F (127) are for ASCII characters, and values #x80 (128) through #x3FFF7F (4194175) are for non-ASCII characters.

Emacs character codes are a superset of the Unicode standard. Values 0 through #x10FFFF (1114111) correspond to Unicode characters of the same codepoint; values #x110000 (1114112) through #x3FFF7F (4194175) represent characters that are not unified with Unicode; and values #x3FFF80 (4194176) through #x3FFFFF (4194303) represent eight-bit raw bytes.

— Function: characterp charcode

This returns t if charcode is a valid character, and nil otherwise. 

          (characterp 65)
               ⇒ t
          (characterp 4194303)
               ⇒ t
          (characterp 4194304)
               ⇒ nil

— Function: max-char

This function returns the largest value that a valid character codepoint can have. 

          (characterp (max-char))
               ⇒ t
          (characterp (1+ (max-char)))
               ⇒ nil
— Function: char-from-name string &optional ignore-case

This function returns the character whose Unicode name is string. If ignore-case is non-nil, case is ignored in string. This function returns nil if string does not name a character. 

          ;; U+03A3
          (= (char-from-name "GREEK CAPITAL LETTER SIGMA") #x03A3)
               ⇒ t
— Function: get-byte &optional pos string

This function returns the byte at character position pos in the current buffer. If the current buffer is unibyte, this is literally the byte at that position. If the buffer is multibyte, byte values of ASCII characters are the same as character codepoints, whereas eight-bit raw bytes are converted to their 8-bit codes. The function signals an error if the character at pos is non-ASCII.

The optional argument string means to get a byte value from that string instead of the current buffer.