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From: dymm@wvucswv.UUCP
Newsgroups: comp.unix.wizards,comp.lang.c,comp.unix.questions
Subject: Lex Macros
Message-ID: <48@wvucswv.UUCP>
Date: Fri, 13-Nov-87 16:21:51 EST
Article-I.D.: wvucswv.48
Posted: Fri Nov 13 16:21:51 1987
Date-Received: Mon, 16-Nov-87 06:30:37 EST
Lines: 40
Keywords: Lex C Macros
Xref: mnetor comp.unix.wizards:5476 comp.lang.c:5436 comp.unix.questions:4921


Dear Friends,

I would like some help in interpreting some of the macros used
in Lex.  Below is the relevant portion of the C code produced by Lex.
The macros are quite "slick", but also somewhat difficult to understand.

Could someone please describe - in detail - how the macros
"input()"  and  "unput()"   operate?????

Send mail to the address below or, if you think your answer is worthy of
the attention of others, post it to the bb.
Thanks for your help.


David Dymm			Software Engineer

USMAIL: Bell Atlantic Knowledge Systems,
	13 Beechurst Ave., Morgantown, WV 26505
PHONE:	304 291-2651 (8:30-4:30 EST)
USENET:  {allegra,bellcore, cadre,idis,psuvax1}!pitt!wvucsb!wvucswv!dymm


	***  C Code From Lex.c  ***
    .
    .
# define U(x) x
# define YYLMAX 200

# define output(c) putc(c,yyout)

# define input() (((yytchar=yysptr>yysbuf?U(*--yysptr):getc(yyin))==10?
    	    	    (yylineno++,yytchar):yytchar)==EOF?0:yytchar)
		    
# define unput(c) {yytchar= (c);if(yytchar=='\n')yylineno--;*yysptr++=yytchar;}

extern char *yysptr, yysbuf[];
int yytchar;
FILE *yyin ={stdin}, *yyout ={stdout};
extern int yylineno;