fortran - Is there anything wrong with passing an unallocated array to a routine without an explicit interface?

Question

Consider:

program main
real, allocatable, dimension(:) :: foo
integer n
n=10
call dofoo(foo,n,1)
allocate(foo(n))
call dofoo(foo,n,0)
end program main

subroutine dofoo(foo,n,mode)
real foo(n)
integer i,n,mode
if(mode.eq.1)then
   n=6
   return
endif
do i=1,n
   foo(i)=i
enddo
return
end subroutine dofoo

Is there anything wrong with the above code? (It works with gfortran) I pass in an un-allocated array the first time, but I don't touch it -- Is there anything in the standard that could cause this to behave in a system dependent way?

Answer 1

You've almost answered your own question. Yes, by the standard, it is always illegal to pass an unallocated allocatable arrays as an actual argument if you don't have an interface in scope.

If you have an interface in scope it is only legal if the dummy argument is also allocatable.

And yes I've been bitten by it. My work around has been to allocate to zero size before the call.