Path: utzoo!mnetor!uunet!husc6!linus!philabs!sbcs!nyit!michael
From: michael@nyit.UUCP (Michael Gwilliam)
Newsgroups: comp.lang.c
Subject: LEX
Message-ID: <260@nyit.UUCP>
Date: 1 Feb 88 22:32:53 GMT
Organization: Computer Graphics Lab, New York Institue of Technology
Lines: 41
Keywords: LEX, comments, C, regular expression
Summary: Is there a regular expression to discard C comments in LEX





I'm writting a C like language to discribe data structures.  When I
was writting the tokenizer using LEX and I got intrigued by a little
problem.  Is it possible to write a regular expression that will
transform a /* comment */ into nothing?

I tried something like  

\/\*[^(\/\*)]*\*\/ ;  

which works pretty good, but won't handle cases like

/*  comment /* more comment */

which is legal in C.  Then somebody came up with something like...

\/\*(.\*)\*\/ ;  

which works pretty good, but it doesn't reject

/* /* nested comment */ */ 

which are illlegal.  So my question is, to all you experienced lex
users and compiler writers, can this be done?  Or do I need to
use input() and other lex functions.  I imagine that the lex code
would be similar in pascal.

Thanks for the help or at least reading this far.

michael

P.S. If reponses are mailed instead of posted, I will be happy to
summerize the results and post them myself, giving proper credit
where it is due.

              nyit!michael
      philabs!nyit!michael
ihnp4!philabs!nyit!michael