Flex/Bison: segmentation fault core dump - c

Question

I'm writing a simple calculator based on .gertrude esolang. What I'm trying to do is parse a text file that contains ratios (in the form of n/m) with flex, than check if the ratio is an index for an operation (+ - / *) or a number and than send the right token to Bison. I get no error when the code are compiled, but when the program is running returns a -segmentation fault core dump - for every kind of input (like 1/2 14/10 1/8 that should be 2 + 8).
Here gertrude.l
%{
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include "gertrude.tab.h"
void yyerror(char *);
int FrazioneToDecimale(char *str1){
int num, den;
unsigned tot;
char *token;
char *deli;
const char del = '/';
*deli = del;
token = strtok (str1, deli);
num = atoi(token);
token = strtok (NULL, deli);
den = atoi(token);
tot = 1 / (num/den);
return tot;
}
%}
%%
/* ratio */
"14/10" {
yylval.sval = '+';
return SOMMA;
}
"11/7" {
yylval.sval = '-';
return SOTTRAZIONE;
}
"6/16" {
yylval.sval = '*';
return MOLTIPLICAZIONE;
}
"5/8" {
yylval.sval = '/';
return DIVISIONE;
}
[0-9]+"/"[0-9]+ {
//yylval = *yytext ;
yylval.ival = FrazioneToDecimale(yytext);
return NUMERO;
}
[ \t] ;
[ \n] { return EOL; };
%%
int yywrap(void) {
return 0;
}
Here gertrude.y
%{
#include <stdio.h>
#include <string.h>
%}
%union {
int ival;
char sval;
}
%type <ival> exp fattore termine
%token <ival> NUMERO
%token <sval> SOMMA SOTTRAZIONE MOLTIPLICAZIONE DIVISIONE
%token EOL
%%
istruzione:
| istruzione exp EOL { printf("= %d\n", $2); }
;
exp: fattore
| exp SOMMA fattore { $$ = $1 + $3; }
| exp SOTTRAZIONE fattore { $$ = $1 - $3; }
;
fattore: termine
| fattore MOLTIPLICAZIONE termine { $$ = $1 * $3; }
| fattore DIVISIONE termine { $$ = $1 / $3; }
;
termine: NUMERO { $$ = $1; }
;
%%
int main(void) {
yyparse();
}
yyerror(char *s) {
fprintf(stderr, "error: %s\n\n", s);
}
Thanks in advance for any kind of advice!

Answer 1

Your code has a problem with pointers and strings. This is a C problem, not a Bison or Flex problem.
Look at these lines from gertrude.l:
char *deli;
const char del = '/';
*deli = del;
Your pointer variable deli is uninitialized and contains garbage, so it might point anywhere. Then you follow that pointer to where it points (anywhere!) and you put a character there. This causes the program to crash. Plus the string (wherever it is) isn't NUL-terminated.
Simply replace those three lines with this line:
char *deli = "/";