NULLIFY

NULLIFY (pointer-object[,pointer-object]...)

説明

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.

例

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

!DIR$ 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