Re: Columns in flex.

C.A.Elliott@dcs.warwick.ac.uk (Charles Elliott) writes:
> [Q: column sensitive scanning in flex? A: track them in the actions]
>
> In the Bison/Yacc part, simply have a semantic instruction that
> compares the value of the variable with the correct amount - obviously you will
> have to declare the variable as an extern to be able to use it in both modules.
>
> If there is a better way, please let me know!


Two small comments:


  * Bison provides the `@N'-Feature to access line/column for
start/end of columns. Read the sections (info nodes) ``Textual
Positions of Tokens'' and ``Special Features for Use in Actions'' of
Bison's documentation for more information.


  * In my experience, it's better to update the column information in
one of the flex supplied hooks, eg, in YY_USER_ACTION. You have to
pay attention to yyunput(), yyless(), and yymore(), 'though. But then,
they don't occur in every action, and it's more easy to maintain the
resulting code.


Cheers,
Joachim
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Joachim Schrod Email: schrod@iti.informatik.th-darmstadt.de
Computer Science Department
Technical University of Darmstadt, Germany
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