问题
On my assignment, I have this description for the String Lexer:
"String literals consist zero or more characters enclosed by double quotes ("). Use escape sequences (listed below) to represent special characters within a string. It is a compile-time error for a new line or EOF character to appear inside a string literal.
All the supported escape sequences are as follows:
\b backspace
\f formfeed
\r carriage return
\n newline
\t horizontal tab
\" double quote
\ backslash
The following are valid examples of string literals:
"This is a string containing tab \t"
"He asked me: \"Where is John?\""
A string literal has a type of string."
And this is my String lexer:
STRINGLIT: '"'(('\\'('b'|'t'|'n'|'f'|'r'|'\"'|'\\'))|~('\n'))*'"';
Can anybody check for my lexer if it meets the requirement or not? If it's not, please tell me your correction, I don't really understand the requirement and ANTLR4.
回答1:
With ANTLR4, instead of writing \\ ('b' | 't' | 'n'), you can write \\ [btn]. Also, as J Earls mentioned in a comment, you'll want to include the quote in your negated set, as well as the \r and the literal \.
This ought to do the trick:
STRINGLIT
: '"' ( '\\' [btnfr"'\\] | ~[\r\n\\"] )* '"'
;
来源：https://stackoverflow.com/questions/39348288/antlr4-need-an-explanation-on-this-string-literals