.C(name, ..., NAOK=FALSE, DUP=TRUE) .Fortran(name, ..., NAOK=FALSE, DUP=TRUE) .External(name, ...)
name
| a character string giving the name of a C function or Fortran subroutine. |
...
| arguments to be passed to the foreign function. |
NAOK
|
if TRUE then any NA or NaN or
Inf values in the arguments are passed on to the foreign function.
If FALSE , the presence of NA or NaN or
Inf values is regarded as an error.
|
DUP
|
if TRUE then arguments are ``duplicated'' before their
address is passed to C or Fortran.
|
.C
and .Fortran
can be used to
make calls to C and Fortran code.
.External
can be used to call
compiled code that uses R objects in the same way as internal R
functions. There is no documentation to help you write this sort of code.
.C
and .Fortran
return a list similar to the ...
list of arguments passed in, but reflecting any
changes made by the C or Fortran code.
.External
returns an R object.
These calls are typically made in conjunction with
dyn.load
which links DLLs to R.
.C
or .Fortran
is
R | C | Fortran |
integer | int * | integer |
real | double * | double precision |
complex | complex * | double precision |
logical | int * | integer |
character | char ** | [compiler dependent] |
list | void * (SEXP *) | |
other | void * (SEXP) |
complex
is defined in `Complex.h' as a
typedef struct {double r; double i;}
.
Note: The C types corresponding to integer
and
logical
are int
, not long
as in S.
Character strings are passed as C arrays of character strings to Fortran: the first string may be usable if its length is passed separately.
Lists, functions, expressions, environments and other language
elements are passed as generic pointers (void *
). R functions can
be invoked using call_S
or call_R
and can be passed
lists or the simple types as arguments.
.External
will typically require access
to the header files in the src/include
. These are not copied by
make install
and so may not be available in an installed version
of R.DUP=FALSE
is dangerous.
There are two important dangers with DUP=FALSE
. The first is that
garbage collection may move the object, resulting in the pointers
pointing nowhere useful and causing hard-to-reproduce bugs.
The second is that if you pass a formal parameter of the calling
function to .C
/.Fortran
with DUP=FALSE
, it may not
necessarily be copied. You may be able to change not only the local
variable but the variable one level up. This will also be very hard to
trace.
1. If your C/Fortran routine calls back any R function including
S_alloc
/R_alloc
then do not use DUP=FALSE
. Do not
even think about it. Calling almost any R function could trigger
garbage collection.
2. If you don't trigger garbage collection it is safe and useful to set
DUP=FALSE
if you don't change any of the variables that might be
affected, e.g.,
.C("Cfunction", input=x, output=numeric(10))
.
In this case the output variable didn't exist before the call so it can't
cause trouble. If the input variable is not changed in Cfunction
you are
safe.
dyn.load
.