Rcpp：C ++函数在R包中不起作用

Question

I have some functions in R and I re-coded them by Rcpp. Each of those functions has a stand-along .cpp file. One function called add_inflow() . Previously, I put all cpp functions on my desktop and used Rcpp::sourceCpp("add_inflow.cpp") . Then, this c++ function could give me an output value by plugging parameters.

Then I want to embed them into my R package called stormwindmodel , by following Compiled Code, R Packages, Hadley

First, I run devtools::use_rcpp() , then moved all cpp functions under src file. Then, I clicked build&reload button and it was succesfully done. At this point, I found the original R functions were in the Environmental Panel but didn't see my cpp functinos. Then I run load_all , and this time cpp functinos showed up. However, when I run add_inflow_Cpp() function, Rstudio gave me this output:

Error in .Call("stormwindmodel_add_forward_speed_Cpp", PACKAGE = "stormwindmodel",  : 
"stormwindmodel_add_forward_speed_Cpp" not available for .Call() for package "stormwindmodel"  

Did I miss any steps? Any suggestion to me?

If the question was not of good enough quality then please give me feedback, I will edit it as soon as possible.

Answer 1

You are likely missing the useDynLib(<pkg>) entry in your NAMESPACE file. If you're using Roxygen and following the examples in the book, you need to include the following content in an R file (the best guess at this point is you missed this step):

#' @useDynLib your-package-name
#' @importFrom Rcpp sourceCpp
NULL

The @useDynLib <pkg> Roxygen directive instructs the roxygen2 package to include a useDynLib(<pkg>) in the NAMESPACE file whenever you re-document the package.

Did you remember to add the associated lines above to an R file in your package in the R folder (eg at R/package-init.R ), and re-document the package after adding that? If you've done everything correctly, you should see useDynLib(<pkg>) added to the NAMESPACE file, with <pkg> replaced by the actual name of your package.

It should be noted that devtools::use_rcpp() does not do this automatically for you -- after running the function, it instructs you that you need to do this step manually:

> devtools::use_rcpp()
Adding Rcpp to LinkingTo and Imports
* Creating `src/`.
* Ignoring generated binary files.
Next, include the following roxygen tags somewhere in your package:

#' @useDynLib sparklyr
#' @importFrom Rcpp sourceCpp
NULL

Then run document()