CODEWITHSUNDEEP
c++cregexflex-lexer
cipher
cipher

Reputation: 2484

Regexp with flex

I am trying to write a flex rule like this:

%%
[0-9]+                  yylval=atoi(yytext); return NUMBER;
[<]                     return LANGLE;
[/>]                    return CLOSERANGLE;
[>]                     return RANGLE;
[/]                     return SLASH;
[ a-zA-Z0-9]            yylval=strdup(yytext); return ANYTHING;
\n                      /* ignore end of line */;
[ \t]+                  /* ignore whitespace */;
%%

When i run a flex program against the file, it says:

example4.l:19: warning, rule cannot be matched
example4.l:20: warning, rule cannot be matched

I guess this is because in the rule [/>] it matches either / or > . But the question is how do i write that rule so that it matches / and > together?

I tried the documentation: It says that: 

‘rs’
    the regular expression ‘r’ followed by the regular expression ‘s’; called concatenation

Am I not doing the same? What's wrong? And how to cope with this?

Upvotes: 0

Views: 164

Answers (1)

rici
rici

Reputation: 241671

I guess this is because in the rule [/>] it matches either / or > .

Exactly.

But the question is how do i write that rule so that it matches / and > together?

"/>"

Am I not doing the same?

No. [/] matches / and [>] matches >. So [/][>] would work. But the quoted form is more normal.

Upvotes: 1

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