J3/03-120

To: J3
From: UK Fortran panel
Subject: Edits for UK comment MTC11 (Separate C data & procedure pointers)
Date: 11 February 2003

Comment MTC11 of the UK vote was:

    Have separate types for C data and procedure pointers.

    Function C_LOC operates on either pointers or functions.  In C,
    pointers and functions are separate and it is confusing to mix them
    in Fortran.  There should be a separate type C_FUNPTR for C
    function pointers.

Here are the edits for this:

381:14. Change "C_PTR and C_NULL_PTR" to "C_PTR, C_FUNPTR, C_NULL_PTR and
   C_NULL_FUNPTR".

382:9 Replace the line by "The entities C_PTR and C_FUNPTR are
   described in 15.2.2.".

382:11. Add to end of paragraph
  "The entity C_NULL_FUNPTR shall be a named constant of type C_FUNPTR.
   The value of C_FUNPTR shall be that of a null pointer to a function."
{We could come right out and say something like "(int (*)(void))0", but
that seems unnecessary.}

383:2+. Change to [really an edit to 03-105r1]

   <<Result Characteristics.>> If X is a procedure, scalar of type
   C_FUNPTR; otherwise, scalar of type C_PTR.

383:16. Change "C_PTR" to "C_PTR or C_FUNPTR".

383:17. Change "type C_PTR" to "the same type as C_PTR_1".

384:5. Change "C_PTR" to "C_PTR or C_FUNPTR".

384:6. Append
  "FPTR shall be a procedure pointer if and only if CPTR is of type
   C_FUNPTR."
{Alternatively and equivalently, "FPTR shall be a data pointer if and
only if CPTR is of type C_PTR.".  Specifying that procedureness must
match seems better than specifying that dataness must match.}

384:6+1-2. Change the sentences "If SHAPE is present ... shall be present" to
  "SHAPE shall be present if and only if CPTR is of type C_PTR and FPTR
   is an array; its size shall be equal to the rank of FPTR."
{As currently written, one is allowed to specify a SHAPE of zero size
when FPTR is scalar.  This is useless: it provides no functionality,
makes errors more likely, and inhibits error detection.}

386:2-3. Replace by

    C_PTR and C_FUNPTR shall be derived types with private components or
    shall be type alias names. C_PTR is interoperable with any C object
    pointer type. C_FUNPTR is interoperable with any C function pointer
    type.

386:3+2. Change "required to have the same representation method for
    all C pointer types" to "required to have the same representation
    method for all C object pointer types and the same representation
    method for all C function pointer types".

386:3+6-7. Change "The function ... is interoperable" to
  "The function C_LOC can be used to return a value of type C_PTR that
   is the C address of an allocated allocatable variable or a value of
   type C_FUNPTR that is the C address of a procedure.  The returned
   value is interoperable"
{"value" is the correct term for the result of a function; entity is
unnecessarily vague - C_LOC does not return a POINTER to a TYPE(C_PTR),
it returns a value of TYPE(C_PTR).}

386:3+10. Change "C_PTR" to "C_FUNPTR or C_PTR".