CODEWITHSUNDEEP
c++tokenflex-lexerlex
T.J.
T.J.

Reputation: 1506

No ouput from lexer in lex and yacc

I am observing a weird behavior while using lex and yacc.

Here is my lex file -- ex.l

%option noyywrap
%option yylineno
%{
#include <iostream>
using namespace std; 

#include "y.tab.h" 
 
void yyerror(char *);  // to get the token types that we return
%}

%%
[ \t] ;

[0-9]+\.[0-9]+ { yylval.fval = atof(yytext); //this is not working 
                 cout << "lex found an float: "; return FLOATS; }
[0-9]+  { cout << "lex found an int: "; yylval.ival = atoi(yytext); return INTS; }
[a-zA-Z0-9]+ {
     
    char *res = new char[strlen(yytext) + 1];
    strcpy(res, yytext);
    yylval.sval = res;
    return STRINGS;
}

. ;

%%

hHre is my yacc file -- ex.y

%{
#include <iostream>
using namespace std ; 

extern int yylex();
extern int yyparse();
extern FILE *yyin;
extern int yynerrs; 
extern void yyerror(char *s);
%}

%union {
    int ival;
    float fval;
    char *sval;
}

%token <ival> INTS
%token <fval> FLOATS
%token <sval> STRINGS

%%

grammar:
    INTS grammar { cout << "yacc found an int: " << $1 << endl; }
    | FLOATS grammar { cout << "yacc found a float: " << $1 << endl; }
    | STRINGS grammar { cout << "yacc found a string: " << $1 << endl; }
    | INTS { cout << "yacc found an int: " << $1 << endl; }
    | FLOATS { cout << "yacc found a float: " << $1 << endl; }
    | STRINGS { cout << "yacc found a string: " << $1 << endl; }
    ;
%%
#include <stdio.h>

 
main() {
     yyin = stdin;
    do {
    yyparse();
    } while (!feof(yyin));
    
}

void yyerror(char *s) {
    cout << "EEK, parse error!  Message: " << s << endl;
    exit(-1);
}

After compiling these two and running them, I don't get the output from the lex for ex:-

output

Why is it happening? Why isn't cout statement in action of lex working?

Upvotes: 2

Views: 329

Answers (1)

Dhananjay
Dhananjay

Reputation: 360

The trouble is I think the following code in ex.y.

%token <ival> INTS
%token <fval> FLOATS
%token <sval> STRINGS

There the inbuilt tokens are used. That overrides the tokens defined in ex.l file. In a sense, the execution never reaches the cout lines in ex.l file.

Try writing only following code & it should work.

%token INTS
%token FLOATS
%token STRINGS

Hope this helps.

NOTE: I have not tested the code. So you may get other errors after doing this.

Upvotes: 1

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