Passing allocatable array to a subroutine

[Alireza_Forghani]

I'm trying to pass an allocatable array, which is already allocated, to a subroutine. something like this:

real(8), dimension(:,:), allocatable :: A

allocate (A (6,6))

call subroutine mysub(A)



subroutine mysub(B)
real (8), dimension (:,:) :: B

write (*,*) B(1,1)

This causes segmentation fault when mysub is accessing B. I have had the same approach to pass the array to a function and it worked fine. I wonder what's going wrong here. 

Thanks,

Alireza

[mecej4]

If you call a subroutine whose arguments include allocatable or assumed-shape arrays, the interface to the subroutine must be provided in the caller. This can be done in a number of ways, and I suggest that you either create and use a module for this purpose or make the subroutine and its caller contained subroutines.

[Martyn_C_Intel]

You need to provide an explicit interface for subroutine B. Otherwise, the caller doesn't know it is supposed to provide all the array bounds information etc., as opposed to just a starting address. You can look up "Doctor Fortran" articles about this, for example, https://software.intel.com/en-us/blogs/2012/01/05/doctor-fortran-gets-explicit-again .

[Alireza_Forghani]

Thanks very much. Now I understand why the function worked, but not the subroutine. The function was defined in a module.