? about pointer variables?

Hello,
can someone tell me why or what of dereferenceing a pointer variable, which has the value NULL? I saw this in the book I was reading and could not find what it meant by that.

Dereferencing a NULL pointer results in a segmentation violation. It's not something you want to happen. ;) Run this and see how a segv occurs on your system:

Code:

---

#include <stdio.h>

int main ( void )
{
  int *p = NULL;
  *p = 10;
  return 0;
}

---

-Prelude

A NULL pointer is a pointer that points to... "nothing". (NULL is defined as 0, or (void*)0 ).

Dereferencing a pointer means using the asterisk to get the value it points to.

Code:

---

// ...
int *pointer;
int a = 7;
pointer = &a;

cout << *pointer << endl; // dereferences pointer and outputs 7

---

Sorry for using cout... as that's C++.. but you get the picture :)

Quote:

---

Originally posted by rmullen3
A NULL pointer is a pointer that points to... "nothing". (NULL is defined as 0, or (void*)0 ).

Dereferencing a pointer means using the asterisk to get the value it points to.

Code:

---

// ...
int *pointer;
int a = 7;
pointer = &a;

cout << *pointer << endl; // dereferences pointer and outputs 7

---

Sorry for using cout... as that's C++.. but you get the picture :)

---

null pointing to zero is a compiler specific thing

Thanks, Prelude, the program "vomitted".

(Like you knew it wouldn't!) :)

The 'type' is undefined, but may be re-defined later. Sans that, get the "barf bags" out!

-Skipper