c - R包: Call C Function Within Rcpp

Question

我正在编写一个包含 C 和 Rcpp 的 R 包。目标是从 R 和 Rcpp 中调用 C 函数，最终在 Rcpp 中执行大部分分析，并且只返回 R 执行最少的任务。我的包编译并从 R 调用我的函数工作正常。

#generate some matrix. Numeric is fine too. Must have column names, no row names
myMat <- matrix(data = 1:100, nrow = 10, ncol = 10,
                dimnames = list(NULL, LETTERS[1:10]))

#This works. Put in full path, no expansion. It returns null to the console.
MinimalExample::WriteMat(mat = myMat, file = "Full_Path_Please/IWork.csv",
                         sep = "," ,eol = "\n", dec = ".", buffMB = 8L)

但是，在 Rcpp 中尝试同样的事情会产生 SIGSEV 错误。我认为问题在于我如何将参数传递给函数，但我想不出正确的方法。

#include <Rcpp.h>

using namespace Rcpp;

extern "C"{
  #include "fwrite.h"
}


//' @export
// [[Rcpp::export]]
void WriteMatCpp(String& fileName, NumericMatrix& testMat){

  Rcpp::Rcout<<"I did start!"<<std::endl;

  String patchName = fileName;
  int whichRow = 1;

  std::string newString = std::string(3 - toString(whichRow).length(), '0') 
                                      + toString(whichRow);
  patchName.replace_last(".csv", newString+".csv");


  //Set objects to pass to print function
  String comma = ",";
  String eol = "\n";
  String dot = ".";
  int buffMem = 8;

  //This is where I crash, giving a SIGSEV error
  fwriteMain(testMat, (SEXP)&patchName, (SEXP)&comma, (SEXP)&eol,
                (SEXP)&dot, (SEXP)&buffMem);

}

这是包含该软件包的 GitHub 存储库的链接。 https://github.com/GilChrist19/MinimalExample

Answer 1

你从 C++ 到 C 的调用是错误的。您不能只在任意数据结构前写上 (SEXP)& 并希望它成为 SEXP。

修复

使用像这样的一行将你在 C++ 中的内容转换为你的 C 函数期望的 SEXP 在每个参数上使用 Rcpp::wrap():

  //This is where I crash, giving a SIGSEV error
  fwriteMain(wrap(testMat), wrap(patchName), wrap(comma), 
             wrap(eol), wrap(dot), wrap(buffMem));

演示

edd@brad:/tmp/MinimalExample/MinEx(master)$ Rscript RunMe.R 
I did start!
edd@brad:/tmp/MinimalExample/MinEx(master)$ cat /tmp/IDoNotWork.csv 
A,B,C,D,E,F,G,H,I,J
1,11,21,31,41,51,61,71,81,91
2,12,22,32,42,52,62,72,82,92
3,13,23,33,43,53,63,73,83,93
4,14,24,34,44,54,64,74,84,94
5,15,25,35,45,55,65,75,85,95
6,16,26,36,46,56,66,76,86,96
7,17,27,37,47,57,67,77,87,97
8,18,28,38,48,58,68,78,88,98
9,19,29,39,49,59,69,79,89,99
10,20,30,40,50,60,70,80,90,100
edd@brad:/tmp/MinimalExample/MinEx(master)$ 

参见 https://github.com/GilChrist19/MinimalExample/tree/master/MinEx一个完整的例子。