ISO C Binding with standard C libraries, and Fortran pointer functions

Question

The ISO-C-Binding extension is mostly working in Sun Fortran, so I have been experimenting with auto-generated interfaces to C libraries, which I hope to develop in to a complete SWIG addition. Ideally, many of the standard C libraries should eventually be commonly available.
One of the problem I realized is that many C library entities are made available via macros. For example, even stdin and stdout are macros by default. The same issues came up when C++ tried to standardize access to C libraries, which resulted in an alternative library to access C functions: http://www.cplusplus.com/reference/clibrary/.
One example is the C 'errno', which is defined as a "modifiable l-value", and traditionally was an external int, but resolves to a function in modern multi-threaded environments. Variations in C libraries probably will require C wrapper functions, but entities like errno can be made to work more like C, if Fortran pointer function results can be handled directly like a normal reference. For example, errno could be accessed as follows:
Fortran source:
program test_errno
use ISO_C_Binding
implicit none
interface
function errno() bind(C,name="cerrno")
use ISO_C_Binding, only: C_int
implicit none
integer(C_int), pointer :: errno
end function errno
end interface
write (*,*) 'errno=',errno()
errno() = 10
write (*,*) 'errno=',errno()
end program test_errno
C source:
#include <errno.h>
int *cerrno(void) { return &errno; }
With the current Sun Fortran, this gives errors. I think that F2008 includes improved specifications involving pointer function results, but I have read through the F2008 draft enough to figure out the details. Ideally, a pointer function result should simply be identical to a temporary pointer variable, instead of lot of complicated specifications involving specific cases. For example, a pointer function returning a derived-type pointer should be able to access a member value like this:
lookup_data("name")%value = 10
where lookup_data is a function returning a pointer to a derived type, which has a member named value.
Does anyone know how F2008 is intended to handle function pointers? Is this something where the details are still incomplete? Is it possible that a complete generalization of function-pointer results is not possible?

Answer 1

The ISO-C-Binding extension is mostly working in Sun Fortran, so I have been experimenting with auto-generated interfaces to C libraries, which I hope to develop in to a complete SWIG addition. Ideally, many of the standard C libraries should eventually be commonly available.
One of the problem I realized is that many C library entities are made available via macros. For example, even stdin and stdout are macros by default. The same issues came up when C++ tried to standardize access to C libraries, which resulted in an alternative library to access C functions: http://www.cplusplus.com/reference/clibrary/.
One example is the C 'errno', which is defined as a "modifiable l-value", and traditionally was an external int, but resolves to a function in modern multi-threaded environments. Variations in C libraries probably will require C wrapper functions, but entities like errno can be made to work more like C, if Fortran pointer function results can be handled directly like a normal reference. For example, errno could be accessed as follows:
Fortran source:
program test_errno
use ISO_C_Binding
implicit none
interface
function errno() bind(C,name="cerrno")
use ISO_C_Binding, only: C_int
implicit none
integer(C_int), pointer :: errno
end function errno
end interface
write (*,*) 'errno=',errno()
errno() = 10
write (*,*) 'errno=',errno()
end program test_errno
C source:
#include <errno.h>
int *cerrno(void) { return &errno; }
With the current Sun Fortran, this gives errors. I think that F2008 includes improved specifications involving pointer function results, but I have read through the F2008 draft enough to figure out the details. Ideally, a pointer function result should simply be identical to a temporary pointer variable, instead of lot of complicated specifications involving specific cases. For example, a pointer function returning a derived-type pointer should be able to access a member value like this:
lookup_data("name")%value = 10
where lookup_data is a function returning a pointer to a derived type, which has a member named value.
Does anyone know how F2008 is intended to handle function pointers? Is this something where the details are still incomplete? Is it possible that a complete generalization of function-pointer results is not possible?