Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!husc6!cmcl2!brl-adm!umd5!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.unix.wizards,comp.lang.c,comp.unix.questions
Subject: Re: Lex Macros
Message-ID: <9390@mimsy.UUCP>
Date: Mon, 16-Nov-87 06:58:49 EST
Article-I.D.: mimsy.9390
Posted: Mon Nov 16 06:58:49 1987
Date-Received: Tue, 17-Nov-87 06:38:08 EST
References: <48@wvucswv.UUCP>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 42
Keywords: Lex C Macros
Xref: mnetor comp.unix.wizards:5480 comp.lang.c:5439 comp.unix.questions:4928

In article <48@wvucswv.UUCP> dymm@wvucswv.UUCP asks what the `input'
and `unput' macros lex generates do.

Try considering them as functions:

	/*
	 * Retrieve an input character.
	 */
	int
	input()
	{
		int c;

		/* retrieve pushback, if any, else next char */
		if (yysptr > yysbuf)
			c = *--yysptr;
		else
			c = getc(yyin);
		/* increment input line number if newline */
		if (c == '\n')
			yylineno++;
		/* return 0 for eof, anything else as is */
		return (c == EOF ? 0 : c);
	}

	unput(c)
		int c;
	{

		/* if pushing back a newline, back the line number down */
		if (c == '\n')
			yylineno--;
		*yysptr++ = c;
	}

The nonsense with the global `yytchar' is to avoid referring to
macro arguments or using `getc' more than once.  It would be nice
if lex used EOF for EOF rather than 0, but not many people need
to scan NULs.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris