16.4.2 Pointer Association

A pointer can be associated with a target. At different times during the execution of a program, a pointer can be undefined, associated with different targets, or be disassociated. The initial association status of a pointer is undefined. A pointer can become associated by the following:

• By pointer assignment (pointer => target)

  The target must be associated, or specified with the TARGET attribute. If the target is allocatable, it must be currently allocated.

• By allocation (successful execution of an ALLOCATE statement)

  The ALLOCATE statement must reference the pointer.

A pointer becomes disassociated if any of the following occur:

• The pointer is nullified by a NULLIFY statement.
  
  
• The pointer is deallocated by a DEALLOCATE statement.
  
  
• The pointer is assigned a disassociated pointer (or the NULL intrinsic function).

When a pointer is associated with a target, the definition status of the pointer is defined or undefined, depending on the definition status of the target. A target is undefined in the following cases:

• If it was never allocated
  
  
• If it is not deallocated through the pointer
  
  
• If a RETURN or END statement causes it to become undefined

If a pointer is associated with a definable target, the definition status of the pointer can be defined or undefined, according to the rules for a variable.

If the association status of a pointer is disassociated or undefined, the pointer must not be referenced or deallocated.

Whatever its association status, a pointer can always be nullified, allocated, or associated with a target. When a pointer is nullified, it is disassociated. When a pointer is allocated, it becomes associated, but is undefined. When a pointer is associated with a target, its association and definition status are determined by its target.

For More Information:

• On pointer assignment, see Section 4.2.3.
  
  
• On the ALLOCATE and DEALLOCATE statements, see Chapter 6.
  
  
• On the NULLIFY statement, see Chapter 6.
  
  
• On the NULL intrinsic function, see Section 9.3.111.