Using C, C++, and Fortran within R and Splus

• R
  • create your C or C++ or Fortran code; you may need to include the header #include "R.h"; if using C++, enclose all your functions with
    extern "C"{
    ... your function code ... 
    }
  • to use Fortran code, I usually call the Fortran function from C or C++; remember to declare the Fortran function, e.g.:
    extern "C" void rkbesld_(double* x,double* alpha,int* nb,int* ize,double* bk, in t* ncalc); // the function would be named rkbesld in the fortran file 
    extern "C" void myfun(int *n,double *x,double* out){ 
    ... function code ... 
    }
  • from the UNIX/Linux command prompt
    >R COMPILE rkbesld.f; R CMD SHLIB file.C rkbesld.o
  • Or, if you're not calling a fortran function, just
    >R CMD SHLIB file.C
  • start R and load the .so file created by the previous step
    >dyn.load("file.so")
  • write and use a wrapper function to access the C/C++ function (see below)
• Splus
  • old UNIX 3.X version:
    from UNIX: >Splus COMPILE file.c
    in S: >dyn.load2("file.o")
  • Linux version:
    >Splus CHAPTER file.{c,f}   # this creates a Makefile; it's ok if you already have chapter created (I think)
    >Splus make  # You may need to change the libraries and linking that are specified in the Makefile created in CHAPTER command
  • write and use a wrapper function to access the C/C++ function (see below)
• wrapper functions
  • the R/S wrapper function deals with the overhead of communicating with C and lets you call your function as if it is in native R/S code, for example, if the function name in file.{c,f} is myfun, create the following wrapper:
    >myfun=function(n, x){ 
       out <- NULL 
       .C("myfun",as.integer(n),as.double(x),as.double(out))[[3]] # returns out (the third element of the list returned by .C) 
    }
    make sure the C/C++/Fortran function has all args passed by reference (i.e., as pointers) and returns void (or else just write a C/C++/Fortran wrapper to do this)