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From: GianLuigi Piacentini on 23 Jul 2010 13:34
Dear Fortraneers,

I would like to test 2 pointers for pointing to the same object:
specifically 2 pointers to list elements like
TYPE element
INTEGER :: payload
TYPE(element), POINTER :: next
END TYPE element
elements are allocated and linked together, and I only know some
current
elements along the list, say cursor_1 and cursor_2, defined as
TYPE cursor
TYPE(element), POINTER :: current
END TYPE cursor
Now I would like to test 2 cursors for pointing to the same element,
say
cursor_1%current%next == cursor_2%current%next
since payloads may be the same. In C I would compare the addresses, but
Fortran automatically dereferences pointers and the expression becomes
a comparison between 2 derived types, and the compiler (G95 0.92)
complains.
Whad do you suggest to solve this ?

Thanks in advance.
G.L. Piacentini

From: Richard Maine on 23 Jul 2010 13:48
GianLuigi Piacentini <ggpiace(a)tin.it> wrote:

> I would like to test 2 pointers for pointing to the same object:

See the 2-argument form of the ASSOCIATED intrinsic. That's exactly what
it does.

(Well, almost exactly. If you have zero-sized array targets, it behaves
in a way I consider counter-intuitive. But as long as your targets don't
have zero size, it gives the "obvious" answer.)

--
Richard Maine | Good judgment comes from experience;
email: last name at domain . net | experience comes from bad judgment.
domain: summertriangle | -- Mark Twain
From: robin on 23 Jul 2010 21:08
"GianLuigi Piacentini" <ggpiace(a)tin.it> wrote in message news:4c49d299$0$40287$4fafbaef(a)reader2.news.tin.it...
| Dear Fortraneers,
|
| I would like to test 2 pointers for pointing to the same object:
| specifically 2 pointers to list elements like
| TYPE element
| INTEGER :: payload
| TYPE(element), POINTER :: next
| END TYPE element
| elements are allocated and linked together, and I only know some
| current
| elements along the list, say cursor_1 and cursor_2, defined as
| TYPE cursor
| TYPE(element), POINTER :: current
| END TYPE cursor
| Now I would like to test 2 cursors for pointing to the same element,
| say
| cursor_1%current%next == cursor_2%current%next

Use the ASSOCIATED builtin for testing whether two
pointers are looking at the same thing.

You can also use it for checkikng whether a pointer is pointing at
anything.


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