.C(.NAME, ..., NAOK = FALSE, DUP = TRUE, PACKAGE, ENCODING) .Fortran(.NAME, ..., NAOK = FALSE, DUP = TRUE, PACKAGE, ENCODING)... list of arguments passed in
(including any names given to the arguments), but reflecting any
changes made by the C or Fortran code.
| R | C |
| Fortran | integer |
| int * | integer |
| numeric | double * |
| double precision | -- or -- |
| float * | real |
| complex | Rcomplex * |
| double complex | logical |
| int * | integer |
| character | char ** |
| [see below] | raw |
| unsigned char * | not allowed |
| list | SEXP * |
| not allowed | other |
| SEXP | not allowed |
double * to C
(and as double precision to Fortran) unless the argument has
attribute Csingle set to TRUE (use
as.single or single). This mechanism is
only intended to be used to facilitate the interfacing of existing C
and Fortran code. The C type Rcomplex is defined in ‘Complex.h’ as a
typedef struct {double r; double i;}. It may or may not be
equivalent to the C99 double complex type, depending on the
compiler used. Logical values are sent as 0 (FALSE), 1
(TRUE) or INT_MIN = -2147483648 (NA, but only if
NAOK = TRUE), and the compiled code should return one of these
three values: however non-zero values other than INT_MIN are
mapped to TRUE. Note: The C types corresponding to integer and
logical are int, not long as in S. This
difference matters on most 64-bit platforms, where int is
32-bit and long is 64-bit (but not on 64-bit Windows). Note: The Fortran type corresponding to logical is
integer, not logical: the difference matters on some
Fortran compilers. Missing (NA) string values are passed to .C as the string
"NA". As the C char type can represent all possible bit patterns
there appears to be no way to distinguish missing strings from the
string "NA". If this distinction is important use .Call. .Fortran passes the first (only) character string of a character
vector is passed as a C character array to Fortran: that may be usable
as character*255 if its true length is passed separately. Only
up to 255 characters of the string are passed back. (How well this
works, and even if it works at all, depends on the C and Fortran
compilers and the platform.) Lists, functions are other R objects can (for historical reasons) be
passed to .C, but the .Call interface is much
preferred. All inputs apart from atomic vectors should be regarded as
read-only, and all apart from vectors (including lists), functions and
environments are now deprecated.DUP = FALSE is dangerous and may be disabled in future
versions of R. It was deprecated in R 3.1.0. People concerned about performance and especially memory usage are
strongly recommended to use the .Call interface instead
of these interfaces. If you pass a local variable to .C/.Fortran with
DUP = FALSE, your compiled code can alter the local variable and
not just the copy in the return list. Worse, if you pass a local
variable that is a formal parameter of the calling function, you may
be able to change not only the local variable but the variable one
level up. This will be very hard to trace. With DUP = FALSE, character vectors cannot be used, and single
precision values will not be returned. It is safe to set DUP = FALSE provided you do not change any of
the variables that might be affected, e.g., .C("Cfunction", input = x, output = numeric(10)). In this case the output variable did not exist before the call
so is not copied (even with DUP = TRUE). If the
input variable is not changed in the C code of Cfunction
you would be safe. Unfortunately, there is no automated check that
the C function does not change its argument, and authors have
frequently done so without realizing it. However, in recent versions of R most unnecessary copying is avoided:
on the other hand using DUP = FALSE can omit necessary
copying..Fortran. Symbol names containing underscores are not valid Fortran 77 (although
they are valid in Fortran 9x). Many Fortran 77 compilers will allow
them but may translate them in a different way to names not containing
underscores. Such names will often work with .Fortran (since
how they are translated is detected when R is built and the
information used by .Fortran), but portable code should not use
Fortran names containing underscores. Use .Fortran with care for compiled Fortran 9x code: it may not
work if the Fortran 9x compiler used differs from the Fortran 77 compiler
used when configuring R, especially if the subroutine name is not
lower-case or includes an underscore. It is also possible to use
.C and do any necessary symbol-name translation yourself.DUP = TRUE there are up to two copies made of each argument
in .... Prior to R 2.15.1 there were always two for vectors (one before
calling the compiled code and one to collect the results), and this is
still the case for character vectors. For other atomic vectors, the
argument is not copied before calling the compiled code if it is not
otherwise used in the calling code (such as output in the
example above). Non-atomic-vector objects are read-only to the C code
and are never copied. This behaviour can be changed by setting
options(CBoundsCheck = TRUE). In that case raw,
logical, integer, double and complex vector arguments are copied both
before and after calling the compiled code. The first copy made is
extended at each end by guard bytes, and on return it is checked that
these are unaltered. For .C, each element of a character
vector uses guard bytes..Call and
.External which are more flexible and have better
performance. These functions are primitive, and .NAME is always
matched to the first argument supplied (which should not be named).
The other named arguments follow ... and so cannot be
abbreviated. For clarity, should avoid using names in the arguments
passed to ... that match or partially match .NAME.
dyn.load, .Call.The ‘Writing R Extensions’ manual.