Re: [Flex-help] help with dangerous trailing context warning

[Aaron S. <aa...@se...>]

First, please let us know what version of flex you're using. There are
some new features available in 2.5.33 and that's important.

This specific message and its causes are documented here:
http://flex.sourceforge.net/manual/Limitations.html

Flex does not implement non-greedy matching, as explained here:
http://flex.sourceforge.net/manual/Why-doesnt-flex-have-non_002dgreedy-operators-like-perl-does_003f.html

What you probably want to do is use a lexer state. For example, here's how
I handle comments in one of my lexers:

%state QSTRING

%%

<QSTRING>([^\"]|\\\"|{CRLF})+ {
                                yylval.sval = strndup(yytext, yyleng);
                                return STRING;
                              }
<QSTRING>\"		      { BEGIN INITIAL; }

<INITIAL>\"                   { BEGIN QSTRING; }


Right, so in the INITIAL state, when we see a quote we go into the QSTRING
state. In QSTRING, we match anything that isn't a quote, is a quoted
quote, or is whitespace. That match stops when it sees an unquoted quote
and returns the string. The next character must be a quote, and the lexer
eats that quote and returns to the INITIAL state.

Aaron


On Thu, Oct 18, 2007, inhahe <in...@gm...> said:

> help!! i'm trying to make a rule that matches r'.*'  and captures only
> what's between the quotes and you can also do r'foo\'bar' but not r'foo\'
> 
> no matter how i try to construct this I get a "dangerous trailing context"
> warning.