

Foreign {base}                               R Documentation

_F_o_r_e_i_g_n _F_u_n_c_t_i_o_n _I_n_t_e_r_f_a_c_e

_D_e_s_c_r_i_p_t_i_o_n_:

     Function to make calls to compiled code that has been
     loaded into R.

_U_s_a_g_e_:

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

_A_r_g_u_m_e_n_t_s_:

    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.

 PACKAGE: if supplied, confine the search for the `name' to
          the DLL given by this argument (plus the conven-
          tional extension, `.so', `.sl', `.dll', ...).
          This is intended to add safety for packages, which
          can ensure that no other package can override
          their external symbols by using this argument.
          Use `PACKAGE="base"' for symbols linked in to R.

_D_e_t_a_i_l_s_:

     The functions `.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.

     `.Call' can be used call compiled code which makes use
     of internal R objects.  The arguments are passed to the
     C code as a sequence of R objects.  It is included to
     provide compatibility with S version 4.

_V_a_l_u_e_:

     The functions `.C' and `.Fortran' return a list similar
     to the `...' list of arguments passed in, but reflect-
     ing any changes made by the C or Fortran code.

     `.External' and `.Call' return an R object.

     These calls are typically made in conjunction with
     `dyn.load' which links DLLs to R.

_A_r_g_u_m_e_n_t _t_y_p_e_s_:

     The mapping of the types of R arguments to C or Fortran
     arguments in `.C' or `.Fortran' is

         R              C             Fortran
      integer       int *         integer
      numeric       double *      double precision
      - or -        float *       real
      complex       complex *     double complex
      logical       int *         integer
      character     char **       [see below]
      list          SEXP *        not allowed
      other         SEXP          not allowed

     Numeric vectors in R will be passed as type `double *'
     to C (and as `double precision' to Fortran) unless (i)
     `.C' or `.Fortran' is used, (ii) `DUP' is false and
     (iii) the argument has attribute `Csingle' set to
     `TRUE' (use `as.single' or `single').  This mechanism
     is only intended to be use to facilitate the interfac-
     ing of existing C and Fortran code.

     The C type `complex' is defined in `Complex.h' as a
     `typedef struct {double r; double i;}'. Fortran type
     `double complex' is an extension to the Fortran stan-
     dard, and the availability of a mapping of `complex' to
     Fortran may be compiler dependent.

     Note: The C types corresponding to `integer' and `logi-
     cal' are `int', not `long' as in S.

     The first character string of a character vector is
     passed as a C character array to Fortran: that string
     may be usable as `character*255' if its true length is
     passed separately. Only up to 255 characters of the
     string are passed back.

     Functions, expressions, environments and other language
     elements are passed as the internal R pointer type
     `SEXP'. This type is defined in `Rinternals.h' or the
     arguments can be declared as generic pointers, `void
     *'. Lists are passed as C arrays of `SEXP' and can be
     declared as `void *' or `SEXP *'.

     R functions can be invoked using `call_S' or `call_R'
     and can be passed lists or the simple types as argu-
     ments.

_H_e_a_d_e_r _f_i_l_e_s _f_o_r _e_x_t_e_r_n_a_l _c_o_d_e_:

     Writing code for use with `.External' and `.Call' will
     use internal R structures. If possible use just those
     defined in `Rinternals.h' and/or the macros in `Rde-
     fines.h', as other header files are not installed and
     are even more likely to be changed.

_N_o_t_e_:

     `DUP=FALSE' is dangerous.

     There are three 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.

     The third is that lists are passed as a single R `SEXP'
     with `DUP=FALSE', not as an array of `SEXP'. This means
     the accessor macros in `Rinternals.h' are needed to get
     at the list elements and the lists cannot be passed to
     `call_S'/`call_R'.

     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 vari-
     able is not changed in `Cfunction' you are safe.

_S_e_e _A_l_s_o_:

     `dyn.load'.

