[escape character] [full of dry goods] super detailed explanation + code illustration!

 

Escape character , seeing the name of a thing one thinks of its function , First , It is One character , Secondly, its meaning has changed , But it is still a character .

stay C In language , Characters are and ascii The tables correspond one by one , Characters can be represented in two ways , One uses it Entity （ That is, the real character , for example 'A'） Express , You can also use a backslash inside single quotation marks to add ascil Code value （ Such as '\130''---->'X' ） Express , This way of using encoded values to indirectly represent characters is called escape characters .

Escape characters to \ perhaps \x start , With \ The beginning represents the encoded value followed by octal form , With \x The beginning represents the encoded value followed by hexadecimal form . For escape characters , Only octal or hexadecimal can be used . These two transfer characters represent A byte Integer value character of size .

\ddd	ddd Express 1~3 Eight octal numbers . Such as \130---->  'X'
\xdd	dd Represents two hexadecimal digits .    Such as \x30 ---> '0'

Students can try printf once "\x48\x45\x4C\x4C\x4F\x20\x57\x4F\x52\x4C\x44\x0A" See what it is .

 

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character 1、2、3、a、b、c Corresponding ASCII The octal forms of the codes are  61、62、63、141、142、143, The hexadecimal forms are  31、32、33、61、62、63.

The following example demonstrates the use of escape characters ：

      Escape characters are intended for ASCII code , So it's The range of values is limited ：

• Escape characters in octal form can be followed by up to three digits , That is to say \ddd, The maximum value is \177-->(127( Decimal system )）;
• Escape characters in hexadecimal form can be followed by up to two numbers , That is to say \xdd, The maximum value is \x7f-->(127( Decimal system )）.

The behavior of escape characters that are out of range is undefined , Some compilers will output the encoded value directly , Some compilers report errors .（ Attached with one ascii surface ）

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But writing like this is a little troublesome , You can't just watch ascii clock , While writing code , So use it to entity like 'A' This is easier , But this will not solve all the problems ,ascii Those in the code Control characters （ Nonprinting characters ） They are invisible , Cannot be displayed on the display , You can't even type... From the keyboard , There is no way to use this direct input method , Only use \ddd perhaps \xdd Way to print , But we know it's troublesome , Use it directly ASCII Code memory is inconvenient , It's not easy to understand , therefore , For common control characters ,C Language is defined again Shorthand way , For example, we use some symbols to help remember to replace numbers , For example, use n To replace hexadecimal digits 'A','\x0A' I can write this as '\n' 了 . The complete list is shown in the figure .

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Escape character	paraphrase	ASCIL Code value
\"	Double quotes	034
\'	Single quotation marks	039
\\	The backslash （ One ）	092
\n	Line break (LF) , Moves the current position to the beginning of the next line	010
\f	Change the page (FF), Move the current position to the beginning of the next page	012
\b	Backspace (BS) , Move the current position to the previous column	008
\a	Ring the bell (BEL)	007
\r	enter (CR) , Move the current position to the beginning of the line	013
\t	Horizontal TAB (HT)	009
\v	Vertical tabulation (VT)	011

 

Let's have a few codes to feel ： Serve ~~~~

1.

Don't get the string length wrong ！\32 Is a character

2.

• Single quotation marks are the beginning and end of character types , To use \' Express , That is to say '\'';
• Double quotes are the beginning and end of a string , To use \" Express , That is to say "abc\"123";
• The backslash is the beginning of the escape character , To use \\ Express , That is to say '\\', perhaps "abc\\123"

3. use \ hold \ If you escape it, you can print out the value we want

Dear comrades, have you learned to waste ~~~

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Blow out the reading lamp , It's all about the moon .

You have to refuel tomorrow .