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From: edw@ius1.cs.cmu.edu (Eddie Wyatt)
Newsgroups: comp.unix.questions
Subject: Re: Any LEX gurus?
Message-ID: <1031@ius1.cs.cmu.edu>
Date: Sat, 8-Aug-87 17:46:20 EDT
Article-I.D.: ius1.1031
Posted: Sat Aug  8 17:46:20 1987
Date-Received: Sun, 9-Aug-87 13:10:05 EDT
References: <716@umnd-cs.D.UMN.EDU>
Organization: Carnegie-Mellon University, CS/RI
Lines: 92
Keywords: Ack!

In article <716@umnd-cs.D.UMN.EDU>, jwabik@cs.D.UMN.EDU (Jeff Wabik) writes:
> I am using (trying to use) LEX (& YACC, of course) to write a parser
> for a language, and I'm running into problems defining some regular
> expressions that need to be fed to LEX.  In short, everything was 
> going fine and I had my parser working 'til I remembered that I 
> needed to completely ignore all preprocessor directives.  Well.. 
> I thought that I could tell LEX to toss out all the preprocessor
> directives, much the same way I was discarding comments:
> 
> 	\{[^\n\}]*\}?		{ ; /* Toss out comments */ }
> 
> The problem here is that (as you'll note) this expression cannot cope with
> comments that contain newlines (which is fine, since neither can the
> compiler 8^), and for the LIFE of me, I CANNOT write an expression
> that WILL accept similar preprocessor directives that NEED to contain
> newlines.  In short, I need to nuke lines that have "??" as the first
> non-white  character of a line, and ending somewhere down the code 
> a bit with another matching "??".  I've tried things similar to:
> 
> 

   What I've done in simuliar situations is to detect the first "??"  then
call a routine to scan to the next "??".  Here's an example :


comment		[\/][\*]
 ....

%%

{comment}		read_comment();
"\n"			linecount++;
{separator}		;
.....


	/* scans til a "*/" is found in the parse file */

static void read_comment()
    {
    register int ch;

    while (TRUE)
        {
        switch (getc(yyin))
            {
            case '*' :
		do
		    {
			/* end of comment */
		    if ((ch = getc(yyin)) == '/') return;

		 	/* should actually be an error - hit EOF before
			 end of comment */
		    if (ch == EOF) return;

			/* found newline - increment line count for
			   error reporting if needed */
		    if (ch == '\n') { linecount++; break; }
		    }
		while (ch == '*');
                break;

            case '\n' :
			/* found newline - increment line count for
			   error reporting if needed */
                linecount++;
                break;

	    case EOF :
		 	/* should actually be an error - hit EOF before
			 end of comment */
	        return;
            }
        }    
    }

> 
> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-==-=-=-=-=-=
> Jeff A. Wabik
> University of Minnesota, Duluth  55812
> 
> ARPA:	jwabik@cs-gw.d.umn.edu		UUCP:  {umn-cs!umnd-cs-gw!jwabik}
> 
> Live long and program.
> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

-- 

					Eddie Wyatt

e-mail: edw@ius1.cs.cmu.edu