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From: rsalz@bbn.com (Rich Salz)
Newsgroups: comp.lang.c
Subject: Re: LEX rule, anyone???
Message-ID: <2191@prune.bbn.com>
Date: 5 Dec 89 15:32:25 GMT
References: <601@vice2utc.chalmers.se>
Organization: BBN Systems and Technologies Corporation
Lines: 44

In <601@vice2utc.chalmers.se> d5kwedb@dtek.chalmers.se (Kristian Wedberg) writes:
>A question from a friend of mine, P{r Eriksson:
>	Does anyone know how to write a LEX rule for C comments,
>	ie for everything between /* and */, nesting not allowed?

We go through this in comp.lang.c about once a year.  Almost everyone
gets it wrong.  The best thing to do is to define a lex rule that
catches "/*" and in the actions for that rule look for */ on your own.

The following code fragment comes from the Cronus type definition compiler:

/* State of our two automata. */
typedef enum _STATE {
    S_EAT, S_STAR, S_NORMAL, S_END
} STATE;

"/*"	        {
		    /* Comment. */
		    register STATE	 S;

		    for (S = S_NORMAL; S != S_END; )
			switch (input()) {
			case '/':
			    if (S == S_STAR) {
				S = S_END;
				break;
			    }
			    /* FALLTHROUGH */
			default:
			    S = S_NORMAL;
			    break;
			case '\0':
			    /* Warn about EOF inside comment? */
			    S = S_END;
			    break;
			case '*':
			    S = S_STAR;
			    break;
			}
		    /* NOTREACHED */
		}
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