(j3.2006) a question on c_f_pointer call

[Jim Xia]

j3-bounces at j3-fortran.org wrote on 08/25/2010 03:18:40 PM:

> [image removed] 
> 
> Re: (j3.2006) a question on c_f_pointer call
> 
> Bill Long 
> 
> to:
> 
> fortran standards email list for J3
> 
> 08/25/2010 03:19 PM
> 
> Sent by:
> 
> j3-bounces at j3-fortran.org
> 
> Please respond to longb, fortran standards email list for J3
> 
> 
> 
> Jim Xia wrote:
> > 
> > We're receiving a customer question on pointer's deallocation status 
for 
> > FPTR from intrinsic c_f_pointer().  Basically the question is whether 
> > user should expect successful deallocation of FPTR from call 
> > c_f_pointer.  This looks pretty much processor dependent since I can't 

> > find clear wording in the standard specifying the behavior.  To be 
> > specific, consider the following three cases
> > 
> > 
> > case 1
> >           use, intrinsic :: iso_c_binding
> >           implicit none
> >           integer stat
> >           type(c_ptr) :: cptr
> >           real(C_DOUBLE), pointer :: p, q
> >           allocate(p)
> >           cptr = c_loc(p)
> >           call c_f_pointer(cptr, q)
> >           deallocate(q, stat=stat)
> >           print *, stat
> >           end
> > 
> 
> This one looks OK.
> 
> > case 2
> >           use, intrinsic :: iso_c_binding
> >           implicit none
> >           integer stat
> >           type(c_ptr) :: cptr
> >           real(C_DOUBLE), pointer :: p, q
> >           real(C_DOUBLE), target :: t
> >           p => t
> >           cptr = c_loc(p)
> >           call c_f_pointer(cptr, q)
> >           deallocate(q, stat=stat)
> >           print *, stat
> >           end
> > 
> 
> This is no legal. See 6.7.3.3 'Deallocation of pointer targets'.  In 
> particular "Deallocating a pointer ... whose target was not created by 
> an ALLOCATE statement causes an error condition in the DEALLOCATE 
> statement".
> 
> 
> > case 3
> >           use, intrinsic :: iso_c_binding
> >           implicit none
> >           integer stat
> >           type(c_ptr) :: cptr
> >           real(C_DOUBLE), pointer :: p, q
> >           real(C_DOUBLE), target, allocatable :: t
> >           allocate (t)
> >           p => t
> >           cptr = c_loc(p)
> >           call c_f_pointer(cptr, q)
> >           deallocate(q, stat=stat)
> >           print *, stat
> >           end
> > 
> 
> Same section.  "If a pointer is associated with an allocatable entity, 
> the pointer shall not be deallocated."
> 
> Cheers,
> Bill
> 
> 
> > 
> > Note these tests are simplified with all pointers being entities 
> > declared in main.  In practice these pointers could be dummy pointers 
> > and the deallocations can happen in different scopes from the 
> > c_f_pointer() function call.
> > 
> > The question is: does standard require specific behavior on each of 
the 
> > DEALLOCATE statement?  I found the standard is vague in this.
> > 
> > Cheers,


What does Cray compiler produce for the three cases?


Jim Xia

XL Fortran Compiler Test
IBM Toronto Lab at 8200 Warden Ave, Markham, On, L6G 1C7
Phone (905) 413-3444  Tie-line 313-3444
email: jimxia at ca.ibm.com
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http://www.ibm.com/software/awdtools/fortran/xlfortran
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