Pointer association

A target that is associated with a pointer can be referenced by a reference to the pointer. This is called pointer association.

A pointer always has an association status:

Associated

The ALLOCATE statement successfully allocates the pointer, which has not been subsequently disassociated or undefined.
```
ALLOCATE (P(3))
```
The pointer is pointer-assigned to a target that is associated or has the TARGET attribute and, if allocatable, is allocated.
```
P => T
```

Disassociated

The pointer is nullified by a NULLIFY statement or by the -qinit=f90ptr option. See -qinit in the XL Fortran Compiler Reference.
```
NULLIFY (P)
```
The pointer is an ultimate component of an object with default initialization specified for the component and:
- a procedure is invoked with this object as an actual argument corresponding to a nonpointer, nonallocatable dummy argument with INTENT(OUT),
- a procedure with the object as an unsaved nonpointer, nonallocatable local object that is not accessed by use or host association is invoked,
- this object is allocated, or
- execution enters a BLOCK construct, and the object is an unsaved, nonpointer, nonallocatable, local variable of the BLOCK construct,
```
TYPE DT
   INTEGER, POINTER :: POINT => NULL()
END TYPE

BLOCK
  TYPE(DT) DT1  ! DT1%POINT becomes disassociated here
END BLOCK
```
The pointer is successfully deallocated.
```
DEALLOCATE (P)
```
The pointer is pointer-assigned to a disassociated pointer.
```
NULLIFY (Q); P => Q
```

Undefined

Initially (unless the -qinit=f90ptr option is specified)
The pointer is an ultimate component of an object, default initialization is not specified for the component, and a procedure is invoked with this object as an actual argument corresponding to a dummy argument with INTENT(OUT), or a procedure is invoked with the pointer as an actual argument corresponding to a pointer dummy argument with INTENT(OUT).
If it is pointer-assigned to a pointer whose association status is undefined.

If its target was deallocated other than through the pointer.

POINTER P(:), Q(:)
ALLOCATE (P(3))
Q => P
DEALLOCATE (Q)   ! Deallocate target of P through Q.
                 ! P is now undefined.
END

If the execution of a RETURN or END statement causes the pointer's target to become undefined.
After the execution of a RETURN or END statement in a procedure where the pointer was declared or accessed, except for objects described in item 4 under Events causing undefinition.

The target of the pointer becomes undefined when execution exits a BLOCK construct.

INTEGER, POINTER :: POINT
BLOCK
  INTEGER, TARGET :: TARG = 2
  POINT => TARG
END BLOCK  ! point becomes undefined here

The pointer is an unsaved, local pointer of a BLOCK construct, and the execution of the BLOCK construct is complete.

Definition status and association status

The definition status of a pointer is that of its target. 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 pointer-assigned. When it is allocated, its definition status is undefined. When it is pointer-assigned, its association and definition status are determined by its target. So, if a pointer becomes associated with a target that is defined, the pointer becomes defined.