How to judge a pointer's target has been deallocated?

[Zhanghong_T_]

Hi all,

We often use associated to judge if a pointer is null or not. But when the target of a pointer has been deallocated, the function associated can't work. Can anyone tell me how to judge it?

Thanks,

Zhanghong Tang

Anexample:

type(test), pointer:: test1, test2

allocate(test1)

test2=>test1

if(associated(test2))then

write(*,*)'associated'

else

write(*,*)'not associated'

endif

deallocate(test1)

! How to judge the target of test2 has been deallocated?????

if(associated(test2))then

write(*,*)'associated'

else

write(*,*)'not associated'

endif

[Zhanghong_T_]

Ican't use the following code:

if(associated(test2, tes1))then

...

Because in real work I don't know test2's target is test1.

[Jugoslav_Dujic]

You can't. Quote from Fortran Standard (2003 draft, but it's the same in F95):

16.4.2.1.3 Events that cause the association status of pointers to become undefined

The association status of a pointer becomes undefined when

25

(1) The pointer is pointer-assigned to a target that has an undefined association status,

(2) The target of the pointer is deallocated other than through the pointer

And Note 16.13:

...the target will cease to exist, leaving the pointer "dangling". This standard considers such pointers to have an undefined association status. They are neither associated nor disassociated. They shall not be used again in the program until their status has been reestablished. There is no requirement on a processor to be able to detect when a pointer target ceases to exist.

I know it doesn't help much, but you will probably have to redesign the program so that it doesn't happen.

Jugoslav