Intel® Fortran Compiler

Developer Guide and Reference

ID 767251
Date 3/31/2025
Public
Document Table of Contents

NULLIFY

Statement: Disassociates a pointer from a target.

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

pointer-object

Is a structure component, the name of a variable, or the name of a procedure pointer. It must have the POINTER attribute. Each pointer-object may not depend on the value, bounds or association of another pointer object in the same NULLIFY statement.

Description

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.

When a polymorphic pointer is nullified, its dynamic type becomes its declared type.

Example

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