创建一个std :: shared_ptr对象并将其返回到R端（Rcpp） [英] Creating a std::shared_ptr object and returning it to the R side (Rcpp)

问题描述

我试图使用Rcpp为C ++脚本编写R绑定。其中一个函数需要一个 std :: shared_ptr对象。我发现难以初始化 std :: shared_ptr obj并将其作为 Rcpp :: XPtr 对象。

I'm trying to write a R bindings for a C++ script using Rcpp. One of the functions expects a std::shared_ptr object. I find it difficult to initialize the std::shared_ptr obj and return it to the R side as a Rcpp::XPtr object.

我试过了（最小例子）：

I've tried (minimal example):

#include <iostream>
#include <memory>
#include <Rcpp.h> 
using namespace Rcpp;
using std::cout;


class TestClass {
  public:
    int value;

    TestClass(int initial_val) {
      value = initial_val;
    };

};


//[[Rcpp::export]]
SEXP get_test_obj() {
  Rcpp::XPtr<std::shared_ptr<TestClass>> ptr(std::make_shared<TestClass>(5), true);
  return ptr;
};

但遇到以下错误：

 no matching function for call to 'Rcpp::XPtr<std::shared_ptr<TestClass> >::XPtr(std::shared_ptr<TestClass>, bool)'

去做这个？

推荐答案

我怀疑R端会有一个std :: shared_ptr传递给它。我假设你的源代码中的一些其他代码依赖于std :: shared_ptr，但你想传递内部原始指针到R.我还假设std :: shared_ptr的生命周期更适当地管理你的代码，因为所提供的代码会使std :: shared_ptr超出函数的范围，并在下一个引用中崩溃。

I doubt that the R side would expect to have a std::shared_ptr passed to it. I'm assuming that some other code in your source relies on std::shared_ptr, but you want to pass the inner raw pointer to R. I'm also assuming that the std::shared_ptr's lifetime is more appropriately managed in your code, since the code as presented would make the std::shared_ptr fall out of scope after the function and crash on the next dereference.

在任何情况下，如果你想传递内部原始指针到R，你会这样做（设计）：

In any case, if you wanted to just pass the inner raw pointer to R, you'd do it like this (contrived):

//[[Rcpp::export]]
SEXP get_test_obj() {
  std::shared_ptr<TestClass> s_ptr = std::make_shared<TestClass>(5);
  Rcpp::XPtr<TestClass> x_ptr(s_ptr.get(), true);
  return x_ptr;
};

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