C language character constant

Doing it C The problem of character constant recognition is encountered in the process of language lexical analyzer . Here we discuss the lexical rules of general character constants , Do not design wide characters and general characters .

character constants

C A language character constant consists of one or more characters contained in single quotes , When multiple characters are included, the specific value is related to the compiler （ such as VS2019 The compiler is to get the last character ）. Such as ：‘a’   ‘XY’   ‘0’   ‘*’
All characters in the source code character set can become character constants , Except for single quotes 、 Backslashes and line breaks , These three characters must be represented by escape characters ：‘\’’   ‘\’   ‘\n’ . In the compilation phase , The characters and escape sequences in character constants and string literals are converted to the corresponding characters in the running character set .

Type and value of character constant

For all non wide character constants , The type is int, namely C There is no difference between character constants and integers in languages , It can be mixed up . The following code can run normally .

int a = 'P';char c = 80;

Here's the thing , If signed char type , Then the value of the character constant can be negative , as follows ：

	int c = '\xA3';
	printf("%c %d\r\n",c,c);

The result is ￡ -93 May adopt unsigned char Such values are positive

Escape character

Refer to the C language norm The second edition