To: J3                                                     11-122
From: John Reid
Subject: Interop: Example re changing attributes
Date: 2011 January 26
References: N1838, N1844, ISO/IEC 1539-1:2010

DISCUSSION

The Fortran programmer might pass an array with one attribute, say
allocatable, to an array with another, say assumed-shape. The Fortran
system takes care of this. From C, the C programmer needs to do a bit
of work.

Edits are provided to show an example.


EDITS to N1838:

[21:17+] At the start of A.2 Clause 5 notes, add the subsection title
"A.2.1 Dummy arguments of any type and rank"

[22:33+] Add

A.2.2 Changing the attributes of an array

A C programmer might want to call more than one Fortran procedure and
the attributes of an array involved might differ between the procedures.
In this case, it is desirable to set up more than one C descriptor for
the array. For example, this code fragment intializes two C descriptors,
calls a procedure that allocates the array described by the first
descriptor, copies the base_addr and dim pointers to the second
descriptor, then calls a procedure that expects an assumed-shape
array.

   cfi_cdest_t desc_alloc, desc_assum;
   int flag
   double d;

   flag = CFI_initialize_cdesc (desc_alloc *, sizeof(d), 2,
              CFI_type_double, CFI_attribute_allocatable);
   flag = CFI_initialize_cdesc (desc_assum *, sizeof(d), 2,
              CFI_type_double, CFI_attribute_assumed);

   Fortran_factor (desc_alloc *, ...)
   desc_assum.base_addr = desc_alloc.base_addr
   desc_assum.dim = desc_alloc.dim
   Fortran_solve (desc_assum *, ...)