(j3.2006) (SC22WG5.3591) Assumed-type and Assumed-rank extensions for C Interop TR.

[Jim Xia]

j3-bounces at j3-fortran.org wrote on 07/25/2008 01:39:28 PM:

> On Friday 25 July 2008 08:52, Jim Xia wrote:
> 
> > And more, I don't understand this fragment
> >
> > type(*),target     :: block(*)
> > integer(8)         :: nbytes
> > Integer(8),pointer :: usable(:)
> >
> > call c_f_pointer (c_loc(block), usable, [nbytes*bit_size(usable)/8] )
> >
> > In particular, I don't understand what c_loc is used for since block 
is
> > already an address. 
> It is an assumed-shape ARRAY, not an address. We don't have that concept 
nor 
> is anyone proposing we add it. It is passed by address, sure, but so are 

> other assumed-shape arrays.

block is an assumed-size array, not assumed-shape.  This fragment doesn't 
demonstrate the "type casting" feature Bill is referring to.  c_loc can be 
called on almost any types that is supported by C.

> 
> > Also I don't see any type "casting" happens here as 
> > the example to demonstrate that.
> You started with an array of unknown type, with which you can do 
> nothing. Then 
> you made a Fortran pointer of a known type (integer) point to it. Now 
you can 
> do things with it. It is like doing:
> 
> usable => block(1:nbytes/8)

This brings another area you have to address: data pointer assignment. The 
type compatibility requirements need to modified to "enable" the "type 
casting".  If an object of TYPE(*) is type compatible with anything, but 
the reverse is not true, then this assignment is illegal (similarly to the 
case that CLASS(*) target can not be pointer assigned to an integer 
pointer, for instance.)  I can't find this in Bill's paper.


Cheers,

Jim Xia

RL 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
D2/YF7/8200 /MKM
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