(j3.2006) INTENT(IN) C_PTR dummy argument of a PURE function

[Bill Long]

On Oct 26, 2015, at 11:02 AM, John Reid <John.Reid at stfc.ac.uk> wrote:

> J3,
> 
> Here is an issue that J3 has discussed. Was it ever resolved?
> 
> Is this code standard conforming?
> 
>     PURE FUNCTION bar_f2c(b) RESULT(p)
>       USE iso_c_binding
>       TYPE(c_ptr), intent(in) :: b
>       TYPE(c_ptr) :: p
>       p = b
>     END FUNCTION bar_f2c
> 
> ifort and gfortran do not fault it, but NAG does because of "Implicit 
> pointer assignment from B?.

Cray and PGI compilers also compile this with no  messages. 

> 
> C1283 in 10-007r1 says:
> 
> In a pure subprogram  ... a dummy argument with the INTENT (IN) 
> attribute, ... shall not be used
> ...
> (2) as the data-target in a pointer-assignment-stmt ,
> ...
> (4) as the expr of an intrinsic assignment statement in which the 
> variable is of a derived type if the derived type has a pointer 
> component at any level of component selection,

The ?pointer? here is a Fortran pointer.  Certainly C_PTR has no component that even remotely resembles a Fortran pointer. 

> ...
> 
> The above code seems to break the spirit of the above rules but not the 
> letter. I think (4) should read
> 
> (4) as the expr of an intrinsic assignment statement in which the 
> variable is of a derived type if the derived type is C_PTR, C_FUNPTR, 
> or has a pointer component at any level of component selection,

So, the argument is that someone could create an argument of type C_PTR that is the C address of a variable in the program, reference this function, and then convert the result to a Fortran pointer via C_F_POINTER.   I think this is a bit beyond the idea that the pure function created a pointer association. 

Cheers,
Bill



> 
> Cheers,
> 
> John.
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Bill Long                                                                       longb at cray.com
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