Foreign Function Interface

Usage

      .C(name, ..., NAOK=FALSE, DUP=TRUE)
.Fortran(name, ..., NAOK=FALSE, DUP=TRUE)

Arguments

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.

Description

The functions .C and .Fortran can be used to make calls to C and Fortran code.

Value

The functions return a list similar to the ... 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.

Note

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.

See Also

dyn.load.


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