Strtok usage, code not working [duplicate]

Question

I am trying to use strtok(). Following is the piece of code that I wrote. It does not work but prints ", '" infinitely.

#include<stdio.h>
#include<stdlib.h>
#include<string.h>

int main(){
char str[]="this, by the way, is a 'sample'";
char *tokens;
tokens = strtok(str, ", '");
//printf("%s\n",tokens);
//printf("%s\n", str);
while(tokens!=NULL)
{
    printf("%s\n", tokens);
    tokens = (NULL, ", '");
}
return 0;
}

Following is the code from a strtok() manual page, which works perfectly fine.

#include <stdio.h>
#include <string.h>

int main ()
{
  char str[] ="- This, a sample string.";
  char * pch;
  printf ("Splitting string \"%s\" into tokens:\n",str);
  pch = strtok (str," ,.-");
  while (pch != NULL)
  {
    printf ("%s\n",pch);
    pch = strtok (NULL, " ,.-");
  }
  return 0;
}

I feel I have done the exact same thing. Can't figure out the fault in my code. Could someone please point out.

Loaves

The duplicate marked this question is complete wrong! in this question OP forgot name of function in codding and because of , comma operator's behavior no error generated While linked question is about the behavior of operator. – Burlington

Answer 1

Interesting bug! You forgot function name. Notice inside while-loop body following expression:

tokens =  (NULL, ",'");
         ^ 
          'strtok' missing 

should be:

tokens = strtok(NULL, ",'");

Interesting thing is that this is not a compilation error, in fact:

tokens = (NULL, ",'");

is a valid expression which is equals to:

tokens = ",'";

(Note: NULL has no side effects)

Read: Comma Operator: ,

The comma operator , has left-to-right associativity. Two expressions separated by a comma are evaluated left to right. The left operand is always evaluated, and all side effects are completed before the right operand is evaluated.

Due to parenthesis ( ) at rhs of =, after evaluating , operator right hand operand "," is assigned to token. And because token never assigned NULL so while(tokens != NULL) never breaks, and this is the reason that you are getting "," infinitely!

Burlington

thanks bro, galti se mistake ho gaya. :). samajh nahi aa raha tha kya galti hai, so i posted – Loaves

@naka no problem, your welcome!.. its obvious mistake :) -- important is to understand why it compiled – Burlington

/*missing calleable-expr*/(expr..., exprn) -- behold, the "coma-operator". Note that the result may not evaluate to exprn in the presence of overloaded operator, – Apothem

@Apothem yes Sehe that is a point but Question is tagged to c – Burlington

Good point. Too bad it kinda spoils a good joke :( Oh well – Apothem