编码

• ASCII
• Unicode
• UTF-8

ASCII

一个字节可表示256个字符，ASCII只用了128个字符

ASCII打印字符对照表

DEC	OCT	HEX	BIN	缩写/符号	HTML实体	描述
0	000	00	00000000	NUL	�	Null char (空字符)
1	001	01	00000001	SOH		Start of Heading (标题开始)
2	002	02	00000010	STX		Start of Text (正文开始)
3	003	03	00000011	ETX		End of Text (正文结束)
4	004	04	00000100	EOT		End of Transmission (传输结束)
5	005	05	00000101	ENQ		Enquiry (请求)
6	006	06	00000110	ACK		Acknowledgment (收到通知)
7	007	07	00000111	BEL		Bell (响铃)
8	010	08	00001000	BS		Back Space (退格)
9	011	09	00001001	HT			Horizontal Tab (水平制表符)
10	012	0A	00001010	LF	
	Line Feed (换行键)
11	013	0B	00001011	VT		Vertical Tab (垂直制表符)
12	014	0C	00001100	FF		Form Feed (换页键)
13	015	0D	00001101	CR	
	Carriage Return (回车键)
14	016	0E	00001110	SO		Shift Out / X-On (不用切换)
15	017	0F	00001111	SI		Shift In / X-Off (启用切换)
16	020	10	00010000	DLE		Data Line Escape (数据链路转义)
17	021	11	00010001	DC1		Device Control 1 (设备控制1)
18	022	12	00010010	DC2		Device Control 2 (设备控制2)
19	023	13	00010011	DC3		Device Control 3 (设备控制3)
20	024	14	00010100	DC4		Device Control 4 (设备控制4)
21	025	15	00010101	NAK		Negative Acknowledgement (拒绝接收)
22	026	16	00010110	SYN		Synchronous Idle (同步空闲)
23	027	17	00010111	ETB		End of Transmit Block (传输块结束)
24	030	18	00011000	CAN		Cancel (取消)
25	031	19	00011001	EM		End of Medium (介质中断)
26	032	1A	00011010	SUB		Substitute (替补)
27	033	1B	00011011	ESC		Escape (溢出)
28	034	1C	00011100	FS		File Separator (文件分割符)
29	035	1D	00011101	GS		Group Separator (分组符)
30	036	1E	00011110	RS		Record Separator (记录分离符)
31	037	1F	00011111	US		Unit Separator (单元分隔符)
32	040	20	00100000		 	Space (空格)
33	041	21	00100001	!	!	Exclamation mark
34	042	22	00100010	"	"	Double quotes
35	043	23	00100011	#	#	Number
36	044	24	00100100	$	$	Dollar
37	045	25	00100101	%	%	Procenttecken
38	046	26	00100110	&	&	Ampersand
39	047	27	00100111	'	'	Single quote
40	050	28	00101000	(	(	Open parenthesis
41	051	29	00101001	)	)	Close parenthesis
42	052	2A	00101010	*	*	Asterisk
43	053	2B	00101011	+	+	Plus
44	054	2C	00101100	,	,	Comma
45	055	2D	00101101	-	-	Hyphen
46	056	2E	00101110	.	.	Period, dot or full stop
47	057	2F	00101111	/	/	Slash or divide
48	060	30	00110000	0	0	Zero
49	061	31	00110001	1	1	One
50	062	32	00110010	2	2	Two
51	063	33	00110011	3	3	Three
52	064	34	00110100	4	4	Four
53	065	35	00110101	5	5	Five
54	066	36	00110110	6	6	Six
55	067	37	00110111	7	7	Seven
56	070	38	00111000	8	8	Eight
57	071	39	00111001	9	9	Nine
58	072	3A	00111010	:	:	Colon
59	073	3B	00111011	;	&#59;	Semicolon
60	074	3C	00111100	<	&#60;	Less than
61	075	3D	00111101	=	&#61;	Equals
62	076	3E	00111110	>	&#62;	Greater than
63	077	3F	00111111	?	&#63;	Question mark
64	100	40	01000000	@	&#64;	At symbol
65	101	41	01000001	A	&#65;	Uppercase A
66	102	42	01000010	B	&#66;	Uppercase B
67	103	43	01000011	C	&#67;	Uppercase C
68	104	44	01000100	D	&#68;	Uppercase D
69	105	45	01000101	E	&#69;	Uppercase E
70	106	46	01000110	F	&#70;	Uppercase F
71	107	47	01000111	G	&#71;	Uppercase G
72	110	48	01001000	H	&#72;	Uppercase H
73	111	49	01001001	I	&#73;	Uppercase I
74	112	4A	01001010	J	&#74;	Uppercase J
75	113	4B	01001011	K	&#75;	Uppercase K
76	114	4C	01001100	L	&#76;	Uppercase L
77	115	4D	01001101	M	&#77;	Uppercase M
78	116	4E	01001110	N	&#78;	Uppercase N
79	117	4F	01001111	O	&#79;	Uppercase O
80	120	50	01010000	P	&#80;	Uppercase P
81	121	51	01010001	Q	&#81;	Uppercase Q
82	122	52	01010010	R	&#82;	Uppercase R
83	123	53	01010011	S	&#83;	Uppercase S
84	124	54	01010100	T	&#84;	Uppercase T
85	125	55	01010101	U	&#85;	Uppercase U
86	126	56	01010110	V	&#86;	Uppercase V
87	127	57	01010111	W	&#87;	Uppercase W
88	130	58	01011000	X	&#88;	Uppercase X
89	131	59	01011001	Y	&#89;	Uppercase Y
90	132	5A	01011010	Z	&#90;	Uppercase Z
91	133	5B	01011011	[	&#91;	Opening bracket
92	134	5C	01011100	\	&#92;	Backslash
93	135	5D	01011101	]	&#93;	Closing bracket
94	136	5E	01011110	^	&#94;	Caret - circumflex
95	137	5F	01011111	_	&#95;	Underscore
96	140	60	01100000	`	&#96;	Grave accent
97	141	61	01100001	a	&#97;	Lowercase a
98	142	62	01100010	b	&#98;	Lowercase b
99	143	63	01100011	c	&#99;	Lowercase c
100	144	64	01100100	d	&#100;	Lowercase d
101	145	65	01100101	e	&#101;	Lowercase e
102	146	66	01100110	f	&#102;	Lowercase f
103	147	67	01100111	g	&#103;	Lowercase g
104	150	68	01101000	h	&#104;	Lowercase h
105	151	69	01101001	i	&#105;	Lowercase i
106	152	6A	01101010	j	&#106;	Lowercase j
107	153	6B	01101011	k	&#107;	Lowercase k
108	154	6C	01101100	l	&#108;	Lowercase l
109	155	6D	01101101	m	&#109;	Lowercase m
110	156	6E	01101110	n	&#110;	Lowercase n
111	157	6F	01101111	o	&#111;	Lowercase o
112	160	70	01110000	p	&#112;	Lowercase p
113	161	71	01110001	q	&#113;	Lowercase q
114	162	72	01110010	r	&#114;	Lowercase r
115	163	73	01110011	s	&#115;	Lowercase s
116	164	74	01110100	t	&#116;	Lowercase t
117	165	75	01110101	u	&#117;	Lowercase u
118	166	76	01110110	v	&#118;	Lowercase v
119	167	77	01110111	w	&#119;	Lowercase w
120	170	78	01111000	x	&#120;	Lowercase x
121	171	79	01111001	y	&#121;	Lowercase y
122	172	7A	01111010	z	&#122;	Lowercase z
123	173	7B	01111011	{	&#123;	Opening brace
124	174	7C	01111100	|	&#124;	Vertical bar
125	175	7D	01111101	}	&#125;	Closing brace
126	176	7E	01111110	~	&#126;	Equivalency sign (tilde)
127	177	7F	01111111		&#127;	Delete

Unicode

将世界所有的符号都纳入其中，每一个符号都有其自己的编码，因此使用Unicode编码没有乱码问题

但是使用Unicode编码，每一个英文字母或汉字都占有2个字节，2个字节最多可编码 2 ^ 16 = 65536 个字符

Unicode兼容ASCII，'a’在ASCII码表是0x61，在Unicode码是ox0061，都对应着97

UTF-8

UTF-8是在互联网使用最广的一种Unicode码的实现

UTF-8是一种变长的编码方式，它可以使用1-6个字节来表示一个符号，根据不同的符号而变化字节的长度

UTF-8字母占一个字节，汉字占3个字节