.C(name, ..., NAOK=FALSE, DUP=TRUE) .Fortran(name, ..., NAOK=FALSE, DUP=TRUE)
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 values in the arguments
are passed on to the foreign function.
If FALSE , the presence of NA 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....
list of arguments passed in, but reflecting any
changes made by the C or Fortran code.
These calls are typically made in conjunction with
dyn.load
which links DLLs to 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
.