Pointer Operators

The unary &, address, operator.

• Takes the address of an object.

      int foo, *bar;
      bar = &foo;         /* The pointer bar contains the address of foo. */
  

• Cannot be done more than one iteration.

      int foo, **bar;
      bar = &(&foo);     /* This is a meaningless statement */
  

The unary *, indirection, operator.

• References the content pointed to by a pointer.

      int foo, *bar;
      bar = &foo;
      *bar = 5;          /* Sets foo to the value 5 */
  

• Can be done for each level of indirection.

      int foo, *bar, **baz;
      bar = &foo;       
      baz = &bar;
      *(*baz) = 5;       /* Sets foo to the value 5 */
  

Pointers and structs, unions

• Using (*ptr).member works, but be careful of precedence.
• New operator ->

      struct foo {
         int member;
      } inst, *ptr;
      ptr = & int;
      (*ptr).member = 2;
      ptr->member = 3;
  

Binary ==, !=.

• You may compare any two pointers of the same type or compatible types.
• Comparing different types may only give a warning at compile time.
• You may also compare against 0.

      char *string;
      long *ptr1, *ptr2;
      if (ptr1 != ptr2);   /* Compare two pointers of the same type */
      if (0 == ptr1);      /* Compare against 0. Same as if (ptr1) */
      if (NULL == ptr1);   /* NULL is defined as a pointer constant */
      if (ptr1 == string); /* XXX Not allowed */
  

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