HP Fortran Programmer's Reference (September 2007)

HP Fortran statements
NULLIFY
Chapter 10 405
NULLIFY
Disassociates a pointer from a target.
Syntax
NULLIFY ( pointer-object-list )
pointer-object-list
is a comma-separated list of variable names and derived-type components.
Description
The NULLIFY statement disassociates a pointer from any target. A NULLIFY statement is also
used to change the status of a pointer from undefined to disassociated.
Examples
The following example shows the declaration and use of a variable with the pointer attribute:
REAL, TARGET :: value ! value can be target
REAL, POINTER :: pt ! for the pointer
pt.pt => value ! Associate pt with value
NULLIFY (pt) ! Disassociate pt
! ASSOCIATED intrinsic is valid in next statement if (and only
! if) pt has been previously allocated, assigned (as above), or
! nullified (as above)
IF (.NOT.ASSOCIATED(pt)) pt => x
The next example shows how a derived type can be used in list processing applications:
TYPE list_node
INTEGER value
TYPE (list_node), POINTER :: next
END TYPE list_node
TYPE (list_node), POINTER :: list
ALLOCATE (list) ! Create new list node
list % value = 28 ! Initialize data field
NULLIFY (list % next) ! Nullify pointer to the next node
Related statements
ALLOCATE, DEALLOCATE, POINTER, and TARGET