Thread: Question related to NULL assignment in pointers to structs

Originally Posted by C_me_run

The assignment here doesn't appear to be necessary, as I've tested pointers to struct without the NULL assignment

That's initialisation, not assignment. The key here is that you have declared these variables outside of a function, so they have static storage duration (this is true even though the static keyword was not used; if you did use it, they would still have static storage duration, but would have internal linkage instead of the external linkage that they have now), and are initialised at startup. If you don't specify any constant for initialisation, they are zero initialised, which for pointers means that they are initialised to be null pointers.

Originally Posted by C_me_run

and when you make the linked list...the next pointer is NULL by default.

How are you making the linked list?

Originally Posted by C_me_run

However, in the interest of preventing un-defined behavior...does assigning NULL like that to those 3 pointers mean the next pointer inside of them is also NULL?

It doesn't, because there is no next pointer inside of them. They are pointers to struct node objects, but not struct node objects themselves, thus they don't have any members, hence they don't have a next pointer member.

Originally Posted by laserlight

That's initialisation, not assignment.

It's initialization and assignment, unless "=" is not an assignment operator (and yes it is)

If you don't specify any constant for initialisation, they are zero initialised, which for pointers means that they are initialised to be null pointers.

No, actually this is not true at all. Let me prove it:

Code:

#include<stdio.h>
int main()
{
  int *value;


  if(!value)
  {
    printf("it's a NULL pointer!\n");
  }
  else
  {
    puts("it's not a NULL pointer\n");
  }


  return 0;
}

Here's the output:

it's not a NULL pointer

And that's the reason I posted this anyway: it seems that the pointer inside of the struct is NULL when I allocate memory for it.