Referencing overlapping arrays through pointers -


i need perform memmove()-style operation pointers tuned overlapping arrays. more precisely, need copy b(:) a(:).

pointers aliasing illustration

in c programming language have called memmove(a, b, n). but, far know, fortran standard strict when comes pointer aliasing.

so, of following 3 options safe use (according standard), , result in undefined behaviour:

  • vector syntax aliased pointers (option 1),
  • explicit do-loop aliased pointers (option 2),
  • call routine takes overlapping arrays arguments (option 3)

?

program ptr   implicit none   integer, parameter :: array_size = 10, n = 6   integer, target :: array(array_size)   integer, dimension(:), pointer :: a, b   integer ::    => array(1: n)   b => array(3: n+2)    ! option 1   a(1: n) = b(1: n)    ! option 2   = 1, n     a(i) = b(i)   end    ! option 3   call foobar(a, b, n)    contains      subroutine foobar(a, b, length)       integer, dimension(:), intent(out) ::       integer, dimension(:), intent(in) :: b       integer, intent(in) :: length        a(1: length) = b(1: length)     end subroutine foobar end program ptr

options 1 , 2 ok, compiler knows pointers can alias.

the subroutine ok per se, cannot pass there 2 aliased arguments, indeed against standard (undefined behaviour c term). can make arguments pointer, aliasing possible , program standard conforming.

  integer, dimension(:), pointer ::   integer, dimension(:), pointer :: b

i deleted intents, because relate pointer association status, not target value, ianh commented. also, fortran2003 required them.


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