fatal error in Bison : start symbole can't derive any sentence

Question

 %token ENTIER REEL VECTOR INTEGER FLOAT CONST READ DISPLAY IF ELSE FOR END AND OR NOT G L GE LE EQ DI ACOUV AT
 %token ACFER AFFEC PLUS MOIN MUL DIV CROOUV CROFER PAROUV PARFER SEP VERG PVERG DEUXPT ESPACE ID CAR CHCAR STRING

 %start S 
 %%
S: ID ACOUV DEC CODE ACFER;

J'ai ce message qui apparait lorse que je fait bison -d prog.y :

fatal error: start symbol S does not derive any sentence

Chris Dodd · Answer 1 · 2014-12-05T22:52:26.397

bison -d on your input gives me:

test.y:6.17-20: symbol CODE is used, but is not defined as a token and has no rules
test.y:6.13-15: symbol DEC is used, but is not defined as a token and has no rules

which tells you exactly what the problem is -- you're using CODE and DEC and not defining them. Add them to one of the %token lines and it works fine...

edit

The error 'start symbol S does not derive any sentence' is telling you that you have unbounded recursion in your grammar, so that no (finite) input can match the start symbol. In you case, S must include a CODE, which must include a command (directly or via a listcommand), which must contain a boucle, which must in turn contain another listcommand. So you end up with an infinite expansion chain of listcommands -> command -> boucle -> listcommands.

The problem is probably your rule

listcommands: command | listcommands ;

which matches exactly one command, plus a useless (and ambiguous) unbounded noop-expansion of that command. You probably want

listcommands: /*epsilon*/ | listcommands command ;

which matches 0 or more commands in sequence. Making this change fixes the fatal error, but still leaves a bunch of shift-reduce conflicts, along with the useless rule dectype: dectype.

To track down and fix shift/reduce conflicts, use bison -v to produce a .output file listing the grammar, states and conflicts in detail. Most of yours come from not having a precedence for NOT, and the other two come from the ambiguous dectype and CODE rules.

i know that, because i don't send you all my code. 'CODE' and 'DEC' are non terminals so i define them in the following of my code but this is not the problem ,the only probem is in the Start — Abderrahmane BECHIKH, Nov 30 '14 at 21:25
Well then, the problem is somewhere in that other code that you're not sharing -- when I add `CODE` and `DEC` to the example above, it works fine, with no errors from bison or otherwise. If you can't post your entire code, you at least need to post something that reproduces the problem. — Chris Dodd, Dec 01 '14 at 01:07

score 0 · Answer 2 · answered Dec 05 '14 at 17:39

this is my code :

 %{#include<stdio.h>
extern FILE* yyin;    
extern tab;    
%}
%union
{char *name;
int num;
 char car;
 }
 %token ENTIER REEL VECTOR INTEGER FLOAT CONST CHAR READ DISPLAY IF ELSE FOR END AND OR NOT G L GE LE EQ DI ACOUV AT
 %token ACFER AFFEC PLUS MOIN MUL DIV CROOUV CROFER PAROUV PARFER SEP VERG PVERG DEUXPT ESPACE ID CAR CHCAR STRING
 %left OR 
 %left AND
 %left G GE EQ DI LE L 
 %left PLUS MOIN 
 %left MUL DIV 
 %start S
 %%
S: ID ACOUV DEC CODE ACFER {printf("Chaine correcte !");YYACCEPT;};
DEC: ACOUV dectype ACFER;
dectype: dectype | type DEUXPT listidf PVERG | VECTOR DEUXPT type DEUXPT ID CROOUV ENTIER VERG     ENTIER CROFER PVERG;
listidf: ID SEP listidf | ID;
type: INTEGER STRING CHAR FLOAT CONST ; 
CODE:ACOUV command ACFER | ACOUV listcommands ACFER;
listcommands: command | listcommands;
command: affichage lecture affectation condition boucle;
affichage: DISPLAY PAROUV CHCAR DEUXPT ID PARFER PVERG;
lecture: READ PAROUV CHCAR DEUXPT AT ID PARFER PVERG;
affectation: ID AFFEC expression PVERG;
expression: expression1 | expressioncond | ID |CONST | PAROUV expression PARFER; 
expressioncond: expression G expression | expression L expression | expression GE expression | expression EQ expression | expression LE expression | expression DI expression |NOT expression | expression OR expression | expression AND expression;
expression1: expression MOIN expression | expression PLUS expression | expression DIV expression | expression MUL expression ;
condition: IF PAROUV expressioncond PARFER listcommands ELSE listcommands END  | IF PAROUV     expressioncond PARFER listcommands END | IF PAROUV expressioncond PARFER condition END;
boucle: FOR PAROUV ID DEUXPT ENTIER conditiondarret PARFER listcommands END;
conditiondarret:ID;
 %%
 int yyerror(char* msg)
 {printf("%s",msg);
  return 1;}
 int main(int argc,char *argv[]) {
     yyin=fopen(argv[1],"r");
     yypase();
     affiche();
     return 0;
 }

fatal error in Bison : start symbole can't derive any sentence

2 Answers2