CODEWITHSUNDEEP
arraysfortran
Sine
Sine

Reputation: 45

Passing a 2D array to a subroutine expecting a 3D array

I need to use a subroutine that expects 3D array as input, but I am dealing with a special case where the third dimension is not required. This subroutine gets called by another one that deals with this special case.

subroutine my_special_case (array)
  real, dimension(:,:)   :: array
  ! some code
  call foo (array)
end subroutine

subroutine foo (array)
  real, dimension(:,:,:) :: array
  ! some code
end subroutine

I could probably just create an allocatable 3D array where to store the values in the 2D one like this

subroutine my_special_case (array)
  real, dimension(:,:)                :: array
  real, allocatable, dimension(:,:,:) :: pass
  ! some code
  allocate( pass( size(array,1), size(array,2), 1) )
  pass(:,:,1) = array(:,:)
  call foo (pass)
end subroutine

but it just feels wasteful and slow to copy the whole array in the second one just to adapt the rank. Is there a better way to do this?

Upvotes: 1

Views: 240

Answers (1)

Vladimir F Героям слава
Vladimir F Героям слава

Reputation: 59998

One of the ways is to use pointer remapping

subroutine my_special_case (array)
  real, dimension(:,:), target   :: array
  real, dimension(:,:,:), pointer :: ptr
  ptr(1:size(array,1), 1:size(array,2), 1:1) => array
  ! some code
  call foo (ptr)
end subroutine

subroutine foo (array)
  real, dimension(:,:,:) :: array
  ! some code
end subroutine

Or you could make foo to accept an explicit size array dimension(nx,ny) or an assumed-size array dimension(nx,*) and just use traditional sequence association.

Upvotes: 2

Related Questions