11-225r1
To: J3
From: Nick Maclaren / Bill Long / Malcolm Cohen
Subject: Interop TR: Fixes to 11-167r2 and 11-175r2
Date: 2011 July 01
Reference: N1854, 11-167r2, 11-175r2


Edits to 11-175r2:
------------------

This is now a rule that the programmer must obey, not a specification
of the effect.

In the last line of the edits to [17:26-28], replace "is source->rank"
by "shall be source->rank".


Edits to 11-167r2:
------------------

The rationale for these is to close certain loopholes where 'clever' C
code could conflict with reasonable Fortran implementations.  Examples
of such code are appended.


In the replacement text of the edits to [15:32-35], replace:

"It shall not point to a C descriptor that is pointed to by a formal
parameter that corresponds to a Fortran actual argument."

by:

"It shall not point to a C descriptor that is pointed to by either a C
formal parameter that corresponds to a Fortran actual argument or a C
actual argument that corresponds to a Fortran dummy argument."


In the replacement text of the edits to [17:12-15], replace:

"If /result/ points to a C descriptor that is pointed to by a formal
parameter that corresponds to a Fortran actual argument, the attribute
member shall not have the value CFI_attribute_assumed."

by:

"If /result/ points to a C descriptor that is pointed to by either a C
formal parameter that corresponds to a Fortran actual argument or a C
actual argument that corresponds to a Fortran dummy argument, the
attribute member shall have the value CFI_attribute_pointer.".


In the replacement text of the edits to [18:9-12], replace:

"If /result/ points to a C descriptor that is pointed to by a formal
parameter that corresponds to a Fortran actual argument, the attribute
member shall not have the value CFI_attribute_assumed."

by:

"If /result/ points to a C descriptor that is pointed to by either a C
formal parameter that corresponds to a Fortran actual argument or a C
actual argument that corresponds to a Fortran dummy argument, the
attribute member shall have the value CFI_attribute_pointer.".


Examples
--------

These are examples of the 'clever' C code that it is intended to forbid.


Example 1:

Subroutine sub(a)
  Real a(:)
  Interface
    Subroutine csub(x) Bind(C)
      Real x(:)
    End Subroutine
  End Interface
  Call csub(a)
  ... do something with a.
End Subroutine
void csub(CFI_desc_t *x)
{
  CFI_establish(x,...); // Zaps a?
}


Example 2:

CFI_desc_t *x;
void start(void)
{
  extern next(CFI_desc_t *y);
  ...
  CFI_establish(x,...);
  ...
  next(x);
  ... do something more with x.
}

Subroutine next(y) Bind(C)
  Real y(:)
  Call zap
  ... do something with y.
End Subroutine

void zap(void)
{
  CFI_establish(x,...); // Zaps Y?
}


Example 3:

CFI_desc_t *x;
void start(void)
{
  extern next1(CFI_desc_t *y);
  ...
  CFI_establish(x,...);
  ...
  next1(x);
  ... do something more with x.
}

Subroutine next1(y) Bind(C)
  Real,Pointer :: y(:)
  Call next2(y)
End Subroutine
Subroutine next2(z) Bind(C)
  Real z(:)
  Call zap
  ... do something with z.
End Subroutine

void zap(void)
{
  CFI_establish(x,...); // Zaps z?
}