less_retarded_wiki/ascii.md

ASCII

ASCII (American standard code for information interchange) is a relatively simple standard for digital encoding of text that's one of the most basic and probably the most common format used for this purpose. For its simplicity and inability to represent characters of less common alphabets it is nowadays quite often replaced with more complex encodings such as UTF-8 who are however almost always backwards compatible with ASCII (interpreting UTF-8 as ASCII will give somewhat workable results), and ASCII itself is also normally supported everywhere. ASCII is the suckless/LRS/KISS character encoding, recommended and good enough for most programs.

The ASCII standard assigns a 7 bit code to each basic text character which gives it a room for 128 characters -- these include lowercase and uppercase English alphabet, decimal digits, other symbols such as a question mark, comma or brackets, plus a few special control characters that represent instructions such as carriage return which are however often obsolete nowadays. Due to most computers working with 8 bit bytes, most platforms store ASCII text with 1 byte per character; the extra bit creates a room for extending ASCII by another 128 characters (or creating a variable width encoding such as UTF-8). These extensions include unofficial ones such as VISCII (ASCII with additional Vietnamese characters) and more official ones, most notably ISO 8859: a group of standards by ISO for various languages, e.g. ISO 88592-1 for western European languages, ISO 8859-5 for Cyrillic languages etc.

The ordering of characters has been kind of cleverly designed to make working with the encoding easier, for example digits start with 011 and the rest of the bits correspond to the digit itself (0000 is 0, 0001 is 1 etc.). Corresponding upper and lower case letters only differ in the 6th bit, so you can easily convert between upper and lower case by negating it as letter ^ 0x20. { I think there is a few missed opportunities though, e.g. in not putting digits right before letters. That way it would be very easy to print hexadecimal (and all bases up to a lot) simply as putchar('0' + x). ~drummyfish }

ASCII was approved as an ANSI standard in 1963 and since then underwent many revisions every few years. The current one is summed up by the following table:

dec	hex	oct	bin	symbol
000	00	000	0000000	NUL: null
001	01	001	0000001	SOH: start of heading
002	02	002	0000010	STX: start of text
003	03	003	0000011	ETX: end of text
004	04	004	0000100	EOT: end of stream
005	05	005	0000101	ENQ: enquiry
006	06	006	0000110	ACK: acknowledge
007	07	007	0000111	BEL: bell
008	08	010	0001000	BS: backspace
009	09	011	0001001	TAB: tab (horizontal)
010	0a	012	0001010	LF: new line
011	0b	013	0001011	VT: tab (vertical)
012	0c	014	0001100	FF: new page
013	0d	015	0001101	CR: carriage return
014	0e	016	0001110	SO: shift out
015	0f	017	0001111	SI: shift in
016	10	020	0010000	DLE: data link escape
017	11	021	0010001	DC1: device control 1
018	12	022	0010010	DC2: device control 2
019	13	023	0010011	DC3: device control 3
020	14	024	0010100	DC4: device control 4
021	15	025	0010101	NAK: not acknowledge
022	16	026	0010110	SYN: sync idle
023	17	027	0010111	ETB: end of block
024	18	030	0011000	CAN: cancel
025	19	031	0011001	EM: end of medium
026	1a	032	0011010	SUB: substitute
027	1b	033	0011011	ESC: escape
028	1c	034	0011100	FS: file separator
029	1d	035	0011101	GS: group separator
030	1e	036	0011110	RS: record separator
031	1f	037	0011111	US: unit separator
032	20	040	0100000	: space
033	21	041	0100001	!
034	22	042	0100010	"
035	23	043	0100011	#
036	24	044	0100100	$
037	25	045	0100101	%
038	26	046	0100110	&
039	27	047	0100111	'
040	28	050	0101000	(
041	29	051	0101001	)
042	2a	052	0101010	*
043	2b	053	0101011	+
044	2c	054	0101100	,
045	2d	055	0101101	-
046	2e	056	0101110	.
047	2f	057	0101111	/
048	30	060	0110000	0
049	31	061	0110001	1
050	32	062	0110010	2
051	33	063	0110011	3
052	34	064	0110100	4
053	35	065	0110101	5
054	36	066	0110110	6
055	37	067	0110111	7
056	38	070	0111000	8
057	39	071	0111001	9
058	3a	072	0111010	:
059	3b	073	0111011	;
060	3c	074	0111100	<
061	3d	075	0111101	=
062	3e	076	0111110	>
063	3f	077	0111111	?
064	40	100	1000000	@
065	41	101	1000001	A
066	42	102	1000010	B
067	43	103	1000011	C
068	44	104	1000100	D
069	45	105	1000101	E
070	46	106	1000110	F
071	47	107	1000111	G
072	48	110	1001000	H
073	49	111	1001001	I
074	4a	112	1001010	J
075	4b	113	1001011	K
076	4c	114	1001100	L
077	4d	115	1001101	M
078	4e	116	1001110	N
079	4f	117	1001111	O
080	50	120	1010000	P
081	51	121	1010001	Q
082	52	122	1010010	R
083	53	123	1010011	S
084	54	124	1010100	T
085	55	125	1010101	U
086	56	126	1010110	V
087	57	127	1010111	W
088	58	130	1011000	X
089	59	131	1011001	Y
090	5a	132	1011010	Z
091	5b	133	1011011	[
092	5c	134	1011100	\
093	5d	135	1011101	]
094	5e	136	1011110	^
095	5f	137	1011111	_
096	60	140	1100000	`: backtick
097	61	141	1100001	a
098	62	142	1100010	b
099	63	143	1100011	c
100	64	144	1100100	d
101	65	145	1100101	e
102	66	146	1100110	f
103	67	147	1100111	g
104	68	150	1101000	h
105	69	151	1101001	i
106	6a	152	1101010	j
107	6b	153	1101011	k
108	6c	154	1101100	l
109	6d	155	1101101	m
110	6e	156	1101110	n
111	6f	157	1101111	o
112	70	160	1110000	p
113	71	161	1110001	q
114	72	162	1110010	r
115	73	163	1110011	s
116	74	164	1110100	t
117	75	165	1110101	u
118	76	166	1110110	v
119	77	167	1110111	w
120	78	170	1111000	x
121	79	171	1111001	y
122	7a	172	1111010	z
123	7b	173	1111011	{
124	7c	174	1111100	`
125	7d	175	1111101	}
126	7e	176	1111110	~
127	7f	177	1111111	DEL

See Also

• Unicode
• ASCII art
• base64