simplercpp

simplercpp is a small demo package incorporating C++ code via Rcpp

This is one of a series of small demo packages for
calling other languages from R:

• {simplec} - calling C with .C()
• {simplecall} - calling C with .Call()
• {simplercpp} - calling C++ with {Rcpp}
• {simplefortran} - calling Fortran with .Fortran()

Rough comparison of .C(), .Call(), {Rcpp} (and .Fortran())

Installation

You can install from GitHub with:

# install.package('remotes')
remotes::install_github('coolbutuseless/simplercpp)

What’s in the box?

Package contains 2 C++ functions, and 2 functions in R (auto-generated by Rcpp) which call the C functions using Rcpp (which uses .Call()).

What’s in the R functions?

• The R functions are auto-created by Rcpp into R/RcppExports.R
• C code is called using .Call()

#' Add 2 numeric vectors
#'
#' @param x,y numeric vectors
#'
#' @return numeric vector
#'
add_rcpp <- function(x, y) {
    .Call(`_simplercpp_add_rcpp`, x, y)
}

What’s in the C functions?

• Numeric vectors in R have a corresponding NumericVector class to use in C++
• roxygen docs on the C code get translated to roxygen docs on the auto-generated R functions
• [[Rcpp::export]] is used to indicate that this function should be made available to the package.

//' Add 2 numeric vectors
//'
//' @param x,y numeric vectors
//'
//' @return numeric vector
//'
// [[Rcpp::export]]
NumericVector add_rcpp(NumericVector x, NumericVector y) {
  return(x + y);
}

What does the C function look like in R?

• An object of class NativeSymbolInfo
• Holds an externalptr to the loaded function

simplercpp:::`_simplercpp_add_rcpp`
#> $name
#> [1] "_simplercpp_add_rcpp"
#> 
#> $address
#> <pointer: 0x7f912ed2c220>
#> attr(,"class")
#> [1] "RegisteredNativeSymbol"
#> 
#> $dll
#> DLL name: simplercpp
#> Filename:
#>         /Library/Frameworks/R.framework/Versions/4.0/Resources/library/simplercpp/libs/simplercpp.so
#> Dynamic lookup: FALSE
#> 
#> $numParameters
#> [1] 2
#> 
#> attr(,"class")
#> [1] "CallRoutine"      "NativeSymbolInfo"

Resources

• David Vaughan’s post - Now you C me
• Peter Dalgaard’s Keynote from UseR 2004 discusses R’s language interfaces
• Using R — Calling C Code ‘Hello World’
• Hadley’s Advanced R book chapter - ‘Rs C interface’
• Rcpp

Acknowledgements

• R Core for developing and maintaining such a wonderful language.
• CRAN maintainers, for patiently shepherding packages onto CRAN and maintaining the repository