two pointers into one 1

[albi73]

Hi dear friens,
I have the following problem that i think might be a solution

suppose to heve the following code:
[code/]
real, dimension(1:3), target :: max
real, dimension(1:4), target :: min
real, dimension), pointer :: p1,p2

p1=>max
p2=>min
[/code]


so far it is all ok.
What i'd like do is the possibility to call all the targets (max and min) by using only one pointer. I'm not able to find a way to define a p3 (pointer) where p3(1),p3(2),p3(3),p3(4),p3(5),p3(6),p3(7) will point to max(1),max(2),max(3),min(1),min(2),min(3),min(4) .


Ciao, Albi

 

[FJacq]

You cannot do that with a "real vector pointer" because the "vector" [max(1),max(2),max(3),min(1),min(2),min(3),min(4)] is not a FORTRAN vector : in a FORTRAN vector there is constant distance (constant stride) between two successive elements.

But you can proceed as follows :

program test

implicit none

type t
  real,pointer :: value
end type

real, dimension(1:3), target :: max
real, dimension(1:4), target :: min
type(t) :: p3(SIZE(max)+size(min))
integer :: i

do i=1,size(max)
  p3(i)%value => max(i)
enddo

do i=1,size(min)
  p3(i+size(max))%value => min(i)
enddo

p3(3)%value = 1
p3(4)%value=2

write(*,*) max(3),min(1)

end program

With the result :

  1.000000       2.000000

Unfortunately, you cannot use p3)%value as a vector of real values because, again, the distance between two successive elements is not constant.





François Jacq

 

[albi73]

Thanks dear FJacq,
again your reply turn on the light of my brain (and it's not so easy, it is really a black box ).
This night going to home I was thinking this soluction, but I didn't understand the real motivation, which is that: poiter, like array, have to respect the costant stride. So I suppose pointers charge the targer address of an array -inheriting the size- only if they are sequential. The gap between max(3) and min(1) causes the problem. Again i can't define p3)%value for the same motivation, but clearly it would like very practical.

The Question: If I want to nullify the pointers i suppose to be compelled to write somethin like:

do i=1,(size(max)+size(min))
  nullify(p3(i)%value)
enddo

 

[FJacq]

Or :

do i=1,(size(max)+size(min))
  p3(i)%value => null()
enddo

But calling nullify is perfect too.

François Jacq