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From: yaqi on 30 Mar 2010 15:46
Hi,

For an integer array, we can do the following:

integer, parameter, dimension(2) :: a =(/1, 2/)

I guess this array will be in the memory before the process starts.

My question is that can we do the similar thing for a user-defined
type, for example,

type mytype
integer, pointer, dimension(:) :: ptr => null()
end type mytype

type(mytype), parameter :: c = mytype(ptr =>(/1,2/))
(the above line is not compilable, it is used only for illustrating
the idea.)

Thanks.
From: glen herrmannsfeldt on 30 Mar 2010 16:19
yaqi <yaqiwang(a)gmail.com> wrote:

> For an integer array, we can do the following:

> integer, parameter, dimension(2) :: a =(/1, 2/)

> I guess this array will be in the memory before the process starts.

I would say that it isn't necessarily in memory at all.

If you want something in memory before the process starts,
usually called static allocation, initialize a variable
(not a parameter).

integer, dimension(2) :: a =(/1, 2/)

(with the implied SAVE attribute.)

> My question is that can we do the similar thing for a user-defined
> type, for example,

> type mytype
> integer, pointer, dimension(:) :: ptr => null()
> end type mytype

> type(mytype), parameter :: c = mytype(ptr =>(/1,2/))
> (the above line is not compilable, it is used only for illustrating
> the idea.)

This leaves about three different questions, all of which I
don't know the answer for.

1) Are structure parameters allowed?

2) Are pointer parameters allowed?

3) Are initialized structures allowed?

4) Are pointers to initialized structures allowed?

I don't believe that I have tried any of those yet in
Fortran, and don't know which are allowed.

-- glen
From: yaqi on 30 Mar 2010 16:26
On Mar 30, 1:46 pm, yaqi <yaqiw...(a)gmail.com> wrote:
> Hi,
>
> For an integer array, we can do the following:
>
> integer, parameter, dimension(2) :: a =(/1, 2/)
>
> I guess this array will be in the memory before the process starts.
>
> My question is that can we do the similar thing for a user-defined
> type, for example,
>
> type mytype
>   integer, pointer, dimension(:) :: ptr => null()
> end type mytype
>
> type(mytype), parameter :: c = mytype(ptr =>(/1,2/))
> (the above line is not compilable, it is used only for illustrating
> the idea.)
>
> Thanks.

With Intel Visual Fortran, the following code is allowed,
type(mytype), parameter :: c = mytype(null())

But I want c%ptr point to something constant during run-time. I want
to set up the constant array during the compiling time although I can
do array assignment at the beginning of run-time.
Unfortunately, the following is not allowed,
type(mytype), parameter :: c = mytype( (/1,2/) )

I found in IVF's documentation "If a component of the derived type is
a pointer, the value in the expression list must evaluate to an object
that would be a valid target in a pointer assignment statement. (A
constant is not a valid target in a pointer assignment statement.)"

But it does not help for this.
From: yaqi on 30 Mar 2010 16:33
On Mar 30, 2:19 pm, glen herrmannsfeldt <g...(a)ugcs.caltech.edu> wrote:
> yaqi <yaqiw...(a)gmail.com> wrote:
> > For an integer array, we can do the following:
> > integer, parameter, dimension(2) :: a =(/1, 2/)
> > I guess this array will be in the memory before the process starts.
>
> I would say that it isn't necessarily in memory at all.
>
> If you want something in memory before the process starts,
> usually called static allocation, initialize a variable
> (not a parameter).
>
> integer, dimension(2) :: a =(/1, 2/)
>
> (with the implied SAVE attribute.)
>
> > My question is that can we do the similar thing for a user-defined
> > type, for example,
> > type mytype
> >  integer, pointer, dimension(:) :: ptr => null()
> > end type mytype
> > type(mytype), parameter :: c = mytype(ptr =>(/1,2/))
> > (the above line is not compilable, it is used only for illustrating
> > the idea.)
>
> This leaves about three different questions, all of which I
> don't know the answer for.
>
> 1) Are structure parameters allowed?
>
> 2) Are pointer parameters allowed?
>
> 3) Are initialized structures allowed?
>
> 4) Are pointers to initialized structures allowed?
>
> I don't believe that I have tried any of those yet in
> Fortran, and don't know which are allowed.
>
> -- glen

Hi Glen,

I've tested the following piece with IVF,
type(mytype), parameter :: c = mytype(null())

, which should answer your questions. But still I can not make c%prt
point to something meaningful.

--yaqi
From: glen herrmannsfeldt on 30 Mar 2010 16:46
yaqi <yaqiwang(a)gmail.com> wrote:
(snip)

> But I want c%ptr point to something constant during run-time. I want
> to set up the constant array during the compiling time although I can
> do array assignment at the beginning of run-time.
> Unfortunately, the following is not allowed,
> type(mytype), parameter :: c = mytype( (/1,2/) )

> I found in IVF's documentation "If a component of the derived type is
> a pointer, the value in the expression list must evaluate to an object
> that would be a valid target in a pointer assignment statement. (A
> constant is not a valid target in a pointer assignment statement.)"

> But it does not help for this.

Yes it does. You don't want a PARAMETER, but an array with
the SAVE attribute. Just as you can't have a pointer to
the constant 1.0, you can't have a pointer to a PARAMETER.

An initialized pointer, which necessarily has the SAVE
attribute, might be able to point to a variable with the
SAVE (and TARGET) attribute. (I am not sure, but it seems
possible.) It couldn't point to a variable without the SAVE
attribute, as that might not have been allocated yet.

-- glen
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