Re: Macro to obtain kind parameter value in F90?

[Rhys Ulerich]

Hi Ralf,

>> Can anyone recommend a macro for obtaining a kind parameter value in
>> Fortran 90?

> Have you looked at the Autoconf Macro Archive?

Nothing there jumped out as a good starting point.

>> The check would be like AC_SIZEOF, but instead of returning the size
>> it would return the kind parameter value (an integer).

> Well, I for one wouldn't know how to do a cross-compile version of
> AC_COMPUTE_INT.

Me neither.  :)

> Does Fortran have a sizeof equivalent?

Some vendors do but there isn't (to my shoddy knowledge) something
standard in F2003 that's fits the sizeof concept.  Even sizeof
wouldn't be enough technically since I don't believe the standard
requires kind parameters to match storage sizes.

> Does it have the notion of types that can differ
> although their internal representation may be the same.

See above about kind parameters not necessarily matching storage sizes.

>> For the curious, I want the value so that I can wrap a C
>> implementation with a public Fortran API that exposes types like
>> REAL(4) instead of REAL(C_FLOAT).  The latter "leaks" ISO_C_BINDING
>> information to clients while the former does not.

> May I ask why the leaking would be a problem?

Hmm..  I though the use of REAL(C_FLOAT) in a function signature would
require the caller to have C_FLOAT in scope to use the function (hence
leaking).  I was mistaken and a simple test case (following signature)
compiles just fine (on systems where C_FLOAT = 4).

Since there's no need for leakage, I don't need such a macro after
all.  It's nice when the problem boils down to just my poor
understanding of the language.

Thank you for your time,
Rhys


! Leakage test case
module testing

  use, intrinsic :: iso_c_binding, only: c_float
  private :: c_float

contains

  real(c_float) function test (x)
    real(c_float), intent(in) :: x(*)
    test = 2 * x(1)
  end function test

end module testing

program main
  use testing
  implicit none
  real(4) :: s(1)
  s = 2.0
  write (*,*) test(s)

end program main