I am trying to learn flex and bison and I started with infix calc example specified in the manual.
Everything is nomal when I use yylex() function specified in the manual. But I wanted to generate tokens using flex and I created following rules and it never worked....:(
I tried to fix this for long time but I am not able to see where I am making a mistake? Please help.
Thanks,
Laxman
/* infix.l */
%{
#include <math.h>
#include <infix.tab.h>
extern int yylval;
%}
WS [ \t\n]
DIGIT [0-9]
%%
{DIGIT}+ { yylval = atoi(yytext); return NUM; }
{WS} ; /* eat empty spaces. */
. return yytext[0];
%%yywrap()
{
return 1;
}/* infix.y */
%{
#define YYSTYPE int
#include <math.h>
#include <stdio.h>
%}
%token NUM
%%
input:
| input line
;
line: '\n'
| exp '\n' { printf ("\t= %d\n", $1); }
;
exp: NUM { $$ = $1; }
| exp '+' exp { $$ = $1 + $3; }
| exp '-' exp { $$ = $1 - $3; }
| exp '*' exp { $$ = $1 * $3; }
| exp '/' exp { $$ = $1 / $3; }
;
%%main()
{
yyparse();
}
yyerror(s)
char *s;
{
printf("%s \n", s);
}commands: $ flex -oinfix.l.c infix.l ; bison -d -oinfix.tab.c infix.y $ gcc -I. -o infix infix.l.c infix.tab.c flex version : 2.5.4 Bison version: 1.875b
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