Pointers

1
Pointers

• Lecture 1
• Thu, Jan 15, 2004

2
Topics

• Pointers
• Declaring Pointers
• Null Pointers
• The Address Operator
• Dereferencing Pointers
• Pointers to Void
• Assignment of Pointers

3
Pointers

• A pointer is an object that refers to another
  object.
• A pointer holds the address of the object that it
  refers to.
• All pointers occupy 4 bytes of memory.

4
Declaring Pointers

• Write the type of object that the pointer points
  to, followed by , followed by the pointer name.

int pi float pf
5
Null Pointers

• A null pointer is a pointer that has the value
  zero.
• A null pointer does not point to any object.
• The constant NULL has the value 0.
• It is a good practice to initialize a pointer to
  NULL.

int pi NULL
6
The Address Operator

• The unary prefix operator returns the address
  of an object.
• The address may be assigned to a pointer.
• Example AddressOperator.cpp

int i int pi i // i is address of i
7
Dereferencing Pointers

• When a pointer is dereferenced, it returns the
  object that it points to.
• The unary pre-fix operator is used to
  dereference a pointer.
• Never dereference a null pointer.
• Example DereferencePointers.cpp

int i 10 int pi i // pi points to i cout
ltlt pi ltlt endl // Print i
8
Pointers to void

• A pointer to void (void object) is a pointer
  that does not point to any particular kind of
  object.
• (void objects do not exist.)
• void is treated as a neutral type for
  situations where the type does not matter.
• A void pointer may hold the address of any
  object.
• A void pointer may not be dereferenced.

9
Assignment of Pointers

• The pointer assignment p1 p2 is legal if and
  only if
• p1 and p2 point to the same type of object, or
• p1 is a pointer to void.
• Otherwise, cast p2 to be compatible with p1.
• Assigning pointers to different types can cause
  serious problems.

10
Example Pointer Assignment

• Example PtrCompatibility.cpp

void pv int pi float pf pv pi pi
(int)pf pf (float)pv