(j3.2006) Question about lbound of an assumed-rank entity

[Bill Long]

On Feb 27, 2017, at 7:35 AM, Bader, Reinhold <Reinhold.Bader at lrz.de> wrote:

> Hello all,
>  
> The answer I arrive at for the program output is
>  
> D)
> 2
> 2
> 2
>  
> I believe the first paragraph cited below only applies to an implementation of c_sub in C. An implementation in Fortran does
> not expose the C descriptor.

When calling a procedure with BIND(C) a Fortran caller does not know what language was used to write the callee. What it does know is that the BIND(C) callee uses the C calling conventions.  So the callee will get the address of a C descriptor as the incoming argument.  Even if it was written in Fortran.

Cheers,
Bill

> (Whether it was a good idea to *not* remap bounds for the nonpointer case of an assumed rank array within Fortran is a separate issue ...)
>  
> Cheers
> Reinhold
>  
> Von: j3-bounces at mailman.j3-fortran.org [mailto:j3-bounces at mailman.j3-fortran.org] Im Auftrag von Daniel C Chen
> Gesendet: Donnerstag, 23. Februar 2017 17:28
> An: j3 at mailman.j3-fortran.org
> Betreff: (j3.2006) Question about lbound of an assumed-rank entity
>  
> Consider the following sample code:
> 
> use, intrinsic :: iso_c_binding
> integer(c_int) :: arr(2:4)
> interface
> subroutine c_sub(arg) BIND(C)
> import
> integer(c_int) :: arg(..)
> end
> subroutine sub(arg)
> integer :: arg(..)
> end
> end interface
> 
> Print*, lbound(arr, 1)
> call c_sub(arr)
> call sub(arr)
> end
> 
> subroutine c_sub(arg) BIND(C)
> use, intrinsic :: iso_c_binding
> integer(c_int) :: arg(..)
> print *, lbound(arg, 1)
> end
> 
> subroutine sub(arg)
> integer :: arg(..)
> print *, lbound(arg, 1)
> End
> 
> Question: Should the output be:
> A):
> 2
> 0
> 2
> 
> B):
> 2
> 1
> 1
> 
> C):
> 2
> 1
> 2
> 
> The standard says: (17-007)
> 
> [497: 12-15]: 
> For a C descriptor of an array pointer or allocatable array, the value of the lower_bound member of each element 
> of the dim member of the descriptor is determined by argument association, allocation, or pointer association.
> For a C descriptor of a nonallocatable nonpointer object, the value of the lower_bound member of each element 
> of the dim member of the descriptor is zero.
> 
> [318: 31-36]:
> An actual argument of any rank may correspond to an assumed-rank dummy argument. The rank and shape
> of the dummy argument are the rank and shape of the corresponding actual argument. If the rank is nonzero,
> the lower and upper bounds of the dummy argument are those that would be given by the intrinsic functions
> LBOUND and UBOUND respectively if applied to the actual argument, except that when the actual argument
> is assumed-size, the upper bound of the last dimension of the dummy argument is 2 less than the lower bound of
> that dimension.
> 
> Based on the above statement, answer A seems to be the correct one...
> 
> Thanks,
> 
> Daniel
> 
> XL Fortran Development, Fortran Standard Representative
> IBM Toronto Software Lab
> Phone: 905-413-3056 
> Tie: 969-3056 
> Email: cdchen at ca.ibm.com
> http://www.ibm.com/software/awdtools/fortran/xlfortran
> 
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Bill Long                                                                       longb at cray.com
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Bioinformatics Software Development                     fax:  651-605-9142
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