[R-pkg-devel] R_registerRoutines, etc.

[Duncan Murdoch]

On 23/04/2017 7:53 PM, Rolf Turner wrote:
> On 24/04/17 11:36, Duncan Murdoch wrote:
>> On 23/04/2017 6:18 PM, Rolf Turner wrote:
>>> On 23/04/17 23:05, Duncan Murdoch wrote:
>>>
>>>>>>
>>>>>> Looks like
>>>>>>
>>>>>> extern void F77_NAME(mnnd)(double *, double *, int *, double *,
>>>>>> double *);
>>>>>>
>>>>>> to me.
>>>
>>> One more (I hope it's the last!) question:
>>>
>>> One of my subroutines has an argument of type *logical*.  There is no
>>> logical type in C.  So, since I am perforce using C-speak, I cannot
>>> change "void *" to "void logical".
>>>
>>
>> For questions like this, see Writing R Extensions section 5.2. "Logical"
>> in R is "int *" in C, and "INTEGER" in Fortran.
>>
>> This is important:  *there is no way to pass a Fortran "LOGICAL" from R
>> to Fortran*.
>>
>> The issue is that different Fortran compilers store LOGICAL in different
>> ways.  Some are equivalent to int with 0 for FALSE, all else for TRUE,
>> but not all are.  So don't rely on it.
>>
>> If you need to call a Fortran subroutine that takes a LOGICAL argument,
>> you need to write another Fortran subroutine that takes an INTEGER
>> argument.  Then compute "arg NE 0" (or whatever the Fortran version is
>> for testing not equal to zero) and pass that to the original routine.
>
> Hoo-boy!!!  Some serious code-rewriting called for!
>
> Thanks for setting me straight on this.
>
> Is it possible that R CMD check could be set up to issue an error, or at
> least a warning, if it finds "logical" or "as.logical" in the argument
> lists of calls to .Fortran()?
>

The problem is at the other end.  Passing an R logical is fine; it just 
turns into an INTEGER on its way to Fortran.

I doubt if it is feasible to detect the problem in Fortran, but static 
analysis keeps getting better, so I could be wrong now or in a while.

Duncan Murdoch



> Seems like it would be a Good Idea if it is indeed possible.
>
> cheers,
>
> Rolf
>