Statement: Disassociates a pointer from a target.
NULLIFY (pointer-object[,pointer-object]...)
pointer-object |
Is a structure component or the name of a variable; it must be a pointer (have the POINTER attribute). |
The initial association status of a pointer is undefined. You can use NULLIFY to initialize an undefined pointer, giving it disassociated status. Then the pointer can be tested using the intrinsic function ASSOCIATED.
The following is an example of the NULLIFY statement:
REAL, TARGET :: TAR(0:50)
REAL, POINTER :: PTR_A(:), PTR_B(:)
PTR_A => TAR
PTR_B => TAR
...
NULLIFY(PTR_A)
After these statements are executed, PTR_A will have disassociated status, while PTR_B will continue to be associated with variable TAR.
The following shows another example:
! POINTER2.F90 Pointing at a Pointer and Target
!DEC$ FIXEDFORMLINESIZE:80
REAL, POINTER :: arrow1 (:)
REAL, POINTER :: arrow2 (:)
REAL, ALLOCATABLE, TARGET :: bullseye (:)
ALLOCATE (bullseye (7))
bullseye = 1.
bullseye (1:7:2) = 10.
WRITE (*,'(/1x,a,7f8.0)') 'target ',bullseye
arrow1 => bullseye
WRITE (*,'(/1x,a,7f8.0)') 'pointer',arrow1
arrow2 => arrow1
IF (ASSOCIATED(arrow2)) WRITE (*,'(/a/)') ' ARROW2 is pointed.'
WRITE (*,'(1x,a,7f8.0)') 'pointer',arrow2
NULLIFY (arrow2)
IF (.NOT.ASSOCIATED(arrow2)) WRITE (*,'(/a/)') ' ARROW2 is not pointed.'
WRITE (*,'( 1x,a,7f8.0)') 'pointer',arrow1
WRITE (*,'(/1x,a,7f8.0)') 'target ',bullseye
END