J3/14-257
To: J3
From: Malcolm Cohen
Subject: C_F_POINTER fixups
Date: 2014 October 13

1. Introduction

The C_F_POINTER extension introduced by the interop TS has poor wording.
There are no examples of C_F_POINTER to help understand the three cases.

2. Edits to 14-007r2

In 15.2.3.3 C_F_POINTER, p3 Arguments, CPTR argument,
[445:11] After "data entity", delete "or"
[445:12] After "noninteroperable argument", change "." -> ", or".
[445:12+] Add new bullet point
  "- the C address of a storage sequence that is not in use by any
     other Fortran entity".

Same para, FPTR argument,
[445:16-19] Make this Case (i).
[445:20-24] Make this Case (ii).
[445:25-446:2] Make this Case (iii).
[445:25] After "address of a storage sequence"
         insert "that is not in use by any other Fortran entity",
[445:27-446:1] Delete ", shall not ... entity,".

[446:4++] After the NOTE 15.3 "... placement in memory.", insert examples

  "Examples.

   Case (i):

     extern double c_x;
     void *address_of_x(void)
     {
       return &c_x;
     }

     ! Assume interface to "address_of_x" is available.
     Real(C_double), Pointer :: xp
     Call C_F_Pointer (address_of_x(), xp)

  Case (ii):

    Type t
      Real,Allocatable :: v(:,:)
    End Type
    Type(t), Target :: x
    Type(C_ptr) :: xloc
    xloc = C_Loc(x)
    ...
    Type(t), Pointer :: y
    Call C_F_Pointer(xloc, y)

  Case (iii)
    void *getmem(int nbits)
    {
       return malloc((nbits+CHAR_BIT-1)/CHAR_BIT);
    }

    ! Assume interface to "getmem" is available,
    ! and there is a derived type "mytype" accessible.
    Type(mytype), Pointer :: x
    Call C_F_Pointer(getmem(Storage_Size(x)), x)"

===END===