segmentation fault (core dumped) Error while calling the mknode function

Question

define YYSTYPE struct node1 *

%token INT FLOAT CHAR DOUBLE VOID

start: Declaration Function Declaration1 {$$ = mknode($1, $2, $3,NULL,0);}

|Declaration Function             {$$=mknode($1,$2,NULL,NULL,0);}   
        
| Declaration                 {$$ =mknode($1,NULL,NULL,NULL,0); }

| Function                {$$ =mknode($1,NULL,NULL,NULL,0); }
;

Declaration1 :Function           {$$ =mknode($1,NULL,NULL,NULL,NULL); }
;


Function: 

Type ID '(' ArgListOpt ')' CompoundStmt         {$$ = mknode($1,$2,$4,$6,NULL); }
;

Type: INT {$$ = mknode(NULL,NULL,NULL,NULL,"INT"); }

| FLOAT {$$ = mknode(NULL,NULL,NULL,NULL,"FLOAT"); }

| CHAR {$$ = mknode(NULL,NULL,NULL,NULL,"CHAR"); }

| DOUBLE {$$ = mknode(NULL,NULL,NULL,NULL,"DOUBLE"); }

| VOID {$$ = mknode(NULL,NULL,NULL,NULL,"VOID"); }

;

CompoundStmt: '{' StmtList '}'      {$$ =$2; }
;

StmtList: StmtList Stmt            {$$ = mknode($1,$2,NULL,NULL,NULL); }

|                   {$$=mknode(NULL,NULL,NULL,NULL,NULL);}
;

when i am running this on the input 

int mian()
{}


it is giving segementation fault at

char* newnode =(char*)malloc(strlen(token));



node1 *mknode(node1 *left1, node1 *left2, node1* left3,node1* left4,char *token)
{

  /* malloc the node */

  node1 *newnode = (node1 *)malloc(sizeof(node1));



  char *newstr = (char *)malloc(strlen(token));

  strcpy(newstr, token);



  newnode->left1 = left1;

  newnode->left2 = left2;

newnode->left3 = left3;

  newnode->left4 = left4;

  newnode->token = newstr;

  return(newnode);
}

what is the error here? plz help

@swati... What you are getting in token??? Please edit token value. — someone
after the removal of segmentation fault now it is showing parsing failed while iam trying to run the program..but before this there was no parsing error..i have parsed the complete program before writing the actions and it was successfully parsing..but now its not..what could be the error — user123
~$ yacc c.y~$ lex c.l ~$ gcc y.tab.c -ll -ly ~$ ./a.out int main() {} 3 : syntax error Parsing failed — user123

Some programmer dude Some programmer dude · Accepted Answer · 2013-08-13T08:43:32

While you should really run your program in a debugger to find it out, these two lines are a likely culprit:

char *newstr = (char *)malloc(strlen(token));

strcpy(newstr, token);

If token is NULL then both strlen and strcpy will most likely crash.

Dereferencing a NULL pointer is undefined behavior and will in most situations cause a crash. Before dereferencing a pointer, or calling a function that does, you need to check if the pointer is NULL or not.

segmentation fault (core dumped) Error while calling the mknode function

define YYSTYPE struct node1 *

1 Answers