Bison/Flex C is having problems parsing second token

Question

I'm doing an assignment, where I have to make Bison/Flex app that would append while/if case beginning at the end every case as a comment. I've managed to compile all the components together, but no matter what I do, it always throws an error after trying to parse the second token.

I'm using Windows versions of Bison and Flex (2.4.1 and 2.5.4a-1 respectively)

Here's my lex file commentAdder.l

%{
#include "commentAdder.tab.h"
%}

%option noyywrap

CLOSE "}"
CASE ("while"|"if"|"switch")(" "|"")("(".+")")(" {"|"{")
CODE .+

%%

{CLOSE} {yylval.s=yytext; return CLOSE;}
{CASE}  {yylval.s=yytext; return CASE;}
{CODE}  {yylval.s=yytext; return CODE;}

%%

And my parser commentAdder.y

%{
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdbool.h>

#define MAX_DEPTH 10
#define MAX_COMMENT_LENGTH 32

int yylex();
void yyerror( char* );
extern char* yytext;

/* Local variables */
char heldComments[MAX_DEPTH][MAX_COMMENT_LENGTH] = {};
int currentDepth=-1;
%}
/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
%union {
  char* s;
}

%token <s> CASE CLOSE CODE
%type <s> expr

%% /* * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

expr    : CLOSE      {$$ = strcat($1,(char *)strcat((char *)"//",heldComments[currentDepth])); 
                      strcpy(heldComments[currentDepth],"");
                      printf("CLOSE: ",$1);
                      currentDepth=currentDepth-1;}
        | CASE       {$$=$1; currentDepth=currentDepth+1; strcpy(heldComments[currentDepth],$1); printf("CASE: ",$1);} 
        | CODE       {printf("CODE: ",$1);$$=$1;}
        ;

%% /* * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

void yyerror( char* s )
{
  fprintf(stderr,"Unexpected token: '%s'\n",yytext);
  exit(1);
}

int main() {  
   yyparse();
   return 0;
}

I'm guessing that expr has nowhere to go after the first parse leaving it with no room for further arguments, but I've no idea how to fix that since I'm a complete novice to this and tutorials are overcomplicated and scarce.

UPDATE

With help of Rici's I've fixed the issue by changing grammar section in parser to this:

 input  : expr {}
        | input expr
 expr   : CLOSE     {if(currentDepth>=0){
                         $$ = strcat($1,(char *)strcat((char *)"//",heldComments[currentDepth]));
 .
 .
 .

Now I have a whole different problem where strcat for some reason causes app to end prematurely, presumably due to error of some kind.

Possibly relevant: stackoverflow.com/questions/62901425/… stackoverflow.com/questions/33068306/bison-only-reads-one-line/… stackoverflow.com/questions/55539786/… — rici
Thanks, this could be it, but I'm not sure how to implement it without bison compiler flipping out. Am I doing this right? adder : expr | adder expr | CLOSE {$$ = str... — Ozzzim
That's hard to read but it looks wrong. You can't drlete the definition of expr without a flood of error messages. — rici
Right, I realised in the meantime you meant in those threads to literally append that code and not make an entirely new grammar to go alongside the original, which I didn't know was a thing. Now it does go through the entire input, but for some reason defaults to CODE after the first argument. Thanks again for your input. — Ozzzim

Ozzzim Ozzzim · Accepted Answer · 2021-02-08T13:33:47

As I stated in the update, I've fixed the main issue. As for the strcat problem, I had to use a additional char[] variable instead of working on raw char*'s

Bison/Flex C is having problems parsing second token

1 Answers