我们可以将Rcpp与多个C ++函数一起使用吗？

Question

I build my own function in .c language. Then, I buit an R function to call the .c function using .C eg,

 tmp <- .C("myfunction",
as.integer(N),
as.integer(n),
as.integer(w1),
as.integer(w2),
as.integer(w3),
PACKAGE = "mypackage")[[3]]

which is called a wraper R function. Also, my function based or requries other .c functions. As I know, using Rcpp make it is more flexiable and easy, such that:

cppFunction('int add(int x, int y, int z) {
  int sum = x + y + z;
  return sum;
}')

I also know that cppFunction works with C++ language. However, I see there is no much different between .c function and .c++ .

My question is: Can I use cppFunction with my .c function that requrie wraper R function? or I need to convert my .c functions into .c++ functions first? What about other function that my function is based on? Does that will be as any regular R function? I mean: suppose I have two cppFunction functions myfunc1 and myfunc2 where myfunc2 based on myfunc1 . Then suppose my second cppFunction is as follows:

cppFunction('int myfunc2(int x, int y, int z) {
      int sum = x + y + z;
      myfunc1 ## do some works here
      return something;
    }')

Is that will be Ok? or Do I need to write it as follow:

cppFunction('int myfunc2(int x, int y, int z) {
      int sum = x + y + z;
      cppFunction('int myfunc2(int some arguments) {## do some works here}
      return something;
    }')

In general how to use build cppFunction that contains multiple functions?

any help please?

Answer 1

Here is an example using an external cpp file. The functions can interact inside the same file, but like others said you have to use header to use function from others files. You have to use // [[Rcpp::export]] before any functions you want available in R.

(Credit to @F.Privé for improving the code)

1) File cpp:

#include <Rcpp.h>
using namespace Rcpp;



// [[Rcpp::export]]
double sumC(NumericVector x) {
  int n = x.size();
  double total = 0;

  for(int i = 0; i < n; ++i) {
    total += x[i];
  }
  return total;
}

// [[Rcpp::export]]
double meanC(NumericVector x) {
  return sumC(x) / x.size();
}

File R:

Rcpp::sourceCpp("your path/mean.cpp")
x <- 1:10
meanC(x)
sumC(x)

2) Alternative approach using cppfunction . You have to use includes argument

cppFunction('double meanC(NumericVector x) {
  return sumC(x) / x.size();
}',includes='double sumC(NumericVector x) {
  int n = x.size();
  double total = 0;

  for(int i = 0; i < n; ++i) {
    total += x[i];
  }
  return total;
}')

Anyway I suggest you to use sourceCpp, using independent files result in much more maintainable and clean code

3) Using sourceCPP and multiple cpp files . You have to use headers file and do an header file for every file.cpp you want to use inside other cpp files.

sum.h file (ifndef prevent multiple definition)

#include <Rcpp.h>
#ifndef SUM1
#define SUM1

double sumC(Rcpp::NumericVector x);

#endif

sum.cpp (like before)

#include <Rcpp.h>
using namespace Rcpp;
// [[Rcpp::export]]
double sumC(NumericVector x) {
  int n = x.size();
  double total = 0;

  for(int i = 0; i < n; ++i) {
    total += x[i];
  }
  return total;
}

mean.cpp file (you have to include sum header) #include "sum.h"

#include <Rcpp.h>
#include "sum.h"
using namespace Rcpp;

// [[Rcpp::export]]
double meanC(NumericVector x) {
  return sumC(x) / x.size();
}