我的目标是建立一个数据集类和一个模型类，并将它们都暴露给R。该模型类有一个train()方法，该方法引用一个数据集实例，这似乎在我问题的根源。这就是它的样子
//glue.cpp
#include <Rcpp.h>
class MyData
{
public:
MyData() = default;
};
class MyModel
{
public:
MyModel() = default;
void train(const MyData& data) { Rcpp::Rcout << "training model... "; };
};
// Expose MyData
RCPP_MODULE(MyData){
Rcpp::class_<MyData>("MyData")
.constructor()
;
}
// Expose MyModel
RCPP_MODULE(MyModel){
Rcpp::class_<MyModel>("MyModel")
.constructor()
.method("train", &MyModel::train)
;
}
（我应该注意，这个文件胶水.cpp嵌入在R包中。）当我删除此行.method("train", &MyModel::train)时，可以通过pkgbuild::compile_dll()进行编译而不会出现错误。有了它，我在下面得到了讨厌的错误
─ installing *source* package ‘SimpleCppModel’ ...
** libs
clang++ -I"/Library/Frameworks/R.framework/Resources/include" -DNDEBUG -I"/Library/Frameworks/R.framework/Versions/3.5/Resources/library/Rcpp/include" -I/usr/local/include -std=c++14 -fPIC -Wall -g -O2 -c RcppExports.cpp -o RcppExports.o
clang++ -I"/Library/Frameworks/R.framework/Resources/include" -DNDEBUG -I"/Library/Frameworks/R.framework/Versions/3.5/Resources/library/Rcpp/include" -I/usr/local/include -std=c++14 -fPIC -Wall -g -O2 -c glue.cpp -o glue.o
In file included from glue.cpp:3:
In file included from /Library/Frameworks/R.framework/Versions/3.5/Resources/library/Rcpp/include/Rcpp.h:27:
In file included from /Library/Frameworks/R.framework/Versions/3.5/Resources/library/Rcpp/include/RcppCommon.h:168:
In file included from /Library/Frameworks/R.framework/Versions/3.5/Resources/library/Rcpp/include/Rcpp/as.h:25:
/Library/Frameworks/R.framework/Versions/3.5/Resources/library/Rcpp/include/Rcpp/internal/Exporter.h:31:28: error: no matching constructor for initialization of 'MyData'
Exporter( SEXP x ) : t(x){}
^ ~
/Library/Frameworks/R.framework/Versions/3.5/Resources/library/Rcpp/include/Rcpp/as.h:87:41: note: in instantiation of member function 'Rcpp::traits::Exporter<MyData>::Exporter' requested here
::Rcpp::traits::Exporter<T> exporter(x);
^
/Library/Frameworks/R.framework/Versions/3.5/Resources/library/Rcpp/include/Rcpp/as.h:152:26: note: in instantiation of function template specialization 'Rcpp::internal::as<MyData>' requested here
return internal::as<T>(x, typename traits::r_type_traits<T>::r_category());
^
/Library/Frameworks/R.framework/Versions/3.5/Resources/library/Rcpp/include/Rcpp/InputParameter.h:72:54: note: in instantiation of function template specialization 'Rcpp::as<MyData>' requested here
ConstReferenceInputParameter(SEXP x_) : obj( as<T>(x_) ){}
^
/Library/Frameworks/R.framework/Versions/3.5/Resources/library/Rcpp/include/Rcpp/module/Module_generated_CppMethod.h:129:58: note: in instantiation of member function 'Rcpp::ConstReferenceInputParameter<MyData>::ConstReferenceInputParameter' requested here
typename Rcpp::traits::input_parameter<U0>::type x0(args[0]);
^
/Library/Frameworks/R.framework/Versions/3.5/Resources/library/Rcpp/include/Rcpp/module/Module_generated_CppMethod.h:127:5: note: in instantiation of member function 'Rcpp::CppMethod1<MyModel, void, const MyData &>::operator()' requested here
CppMethod1( Method m) : method_class(), met(m) {}
^
/Library/Frameworks/R.framework/Versions/3.5/Resources/library/Rcpp/include/Rcpp/module/Module_generated_method.h:59:27: note: in instantiation of member function 'Rcpp::CppMethod1<MyModel, void, const MyData &>::CppMethod1' requested here
AddMethod( name_, new CppMethod1<Class,RESULT_TYPE,U0>(fun), valid, docstring);
^
glue.cpp:30:4: note: in instantiation of function template specialization 'Rcpp::class_<MyModel>::method<void, const MyData &>' requested here
.method("train", &MyModel::train)
^
glue.cpp:5:7: note: candidate constructor (the implicit copy constructor) not viable: cannot convert argument of incomplete type 'SEXP' (aka 'SEXPREC *') to 'const MyData' for 1st argument
class MyData
^
glue.cpp:5:7: note: candidate constructor (the implicit move constructor) not viable: cannot convert argument of incomplete type 'SEXP' (aka 'SEXPREC *') to 'MyData' for 1st argument
glue.cpp:8:3: note: candidate constructor not viable: requires 0 arguments, but 1 was provided
MyData() = default;
^
1 error generated.
make: *** [glue.o] Error 1
ERROR: compilation failed for package ‘SimpleCppModel’
─ removing ‘/private/var/folders/dn/9lp6j6j14t1137ftnnk27wyw0000gn/T/RtmpBqDLoF/devtools_install_4d775ed17ea2/SimpleCppModel’
Error in processx::run(bin, args = real_cmdargs, stdout_line_callback = real_callback(stdout), :
System command error
有什么作用？
答案 0 :(得分：3)
正如Dirk在评论中所提到的，您将需要as<>的{{1}}和wrap专业化知识。在您的情况下，可以使用“扩展Rcpp”小插图中最简单的解决方案：MyData。 当您包含Rcpp中的哪个标头时，您只需要小心：
RCPP_EXPOSED_CLASS正如您在答案中发现的那样，它甚至在之后（包括#include <Rcpp.h>
class MyData
{
public:
MyData() = default;
};
RCPP_EXPOSED_CLASS(MyData)
class MyModel
{
public:
MyModel() = default;
void train(const MyData& data) { Rcpp::Rcout << "training model... " << std::endl; };
};
// Expose MyData
RCPP_MODULE(MyData){
Rcpp::class_<MyData>("MyData")
.constructor()
;
}
// Expose MyModel
RCPP_MODULE(MyModel){
Rcpp::class_<MyModel>("MyModel")
.constructor()
.method("train", &MyModel::train)
;
}
/***R
myData <- new(MyData)
myModel <- new(MyModel)
myModel$train(myData)
*/
）都有效。
不过，仔细阅读提到的画廊文章和小插图仍然有意义。
答案 1 :(得分：2)
首先，我应该指出问题中的示例过于简单。实际上，MyData类具有$db = mysqli_connect('localhost', 'root', '', 'multi_login');
// variable declaration
$username = "";
$firstname = "";
$lastname = "";
$errors = array();
// call the register() function if register_btn is clicked
if (isset($_POST['register_btn'])) {
register();
}
// call the login() function if register_btn is clicked
if (isset($_POST['login_btn'])) {
login();
}
if (isset($_GET['logout'])) {
session_destroy();
unset($_SESSION['user']);
header("location: ../login.php");
}
// REGISTER USER
function register(){
global $db, $errors;
// receive all input values from the form
$username = e($_POST['username']);
$firstname = e($_POST['firstname']);
$lastname = e($_POST['lastname']);
$password_1 = e($_POST['password_1']);
$password_2 = e($_POST['password_2']);
// form validation: ensure that the form is correctly filled
if (empty($username)) {
array_push($errors, "Username is required");
}
if (empty($firstname)) {
array_push($errors, "First Name is required");
}
if (empty($lastname)) {
array_push($errors, "Last Name is required");
}
if (empty($password_1)) {
array_push($errors, "Password is required");
}
if ($password_1 != $password_2) {
array_push($errors, "The two passwords do not match");
}
// register user if there are no errors in the form
if (count($errors) == 0) {
$password = md5($password_1);//encrypt the password before saving in the database
if (isset($_POST['user_type'])) {
$user_type = e($_POST['user_type']);
$query = "INSERT INTO users (username, firstname, lastname, user_type, password)
VALUES('$username', '$firstname', '$lastname', '$user_type', '$password')";
mysqli_query($db, $query);
$_SESSION['success'] = "New user successfully created!!";
header('location: home.php');
}else{
$query = "INSERT INTO users (username, firstname, lastname, user_type, password)
VALUES('$username', '$firstname', '$lastname', 'user', '$password')";
mysqli_query($db, $query);
// get id of the created user
$logged_in_user_id = mysqli_insert_id($db);
$_SESSION['user'] = getUserById($logged_in_user_id); // put logged in user in session
$_SESSION['success'] = "You are now logged in";
header('location: index.php');
}
}
}
// return user array from their id
function getUserById($id){
global $db;
$query = "SELECT * FROM users WHERE id=" . $id;
$result = mysqli_query($db, $query);
$user = mysqli_fetch_assoc($result);
return $user;
}
// LOGIN USER
function login(){
global $db, $username, $errors;
// grap form values
$username = e($_POST['username']);
$password = e($_POST['password']);
// make sure form is filled properly
if (empty($username)) {
array_push($errors, "Username is required");
}
if (empty($password)) {
array_push($errors, "Password is required");
}
// attempt login if no errors on form
if (count($errors) == 0) {
$password = md5($password);
$query = "SELECT * FROM users WHERE username='$username' AND password='$password' LIMIT 1";
$results = mysqli_query($db, $query);
if (mysqli_num_rows($results) == 1) { // user found
// check if user is admin or user
$logged_in_user = mysqli_fetch_assoc($results);
if ($logged_in_user['user_type'] == 'admin') {
$_SESSION['user'] = $logged_in_user;
$_SESSION['success'] = "You are now logged in";
header('location: admin/home.php');
}else{
$_SESSION['user'] = $logged_in_user;
$_SESSION['success'] = "You are now logged in";
header('location: index.php');
}
}else {
array_push($errors, "Wrong username/password combination");
}
}
}
function isLoggedIn()
{
if (isset($_SESSION['user'])) {
return true;
}else{
return false;
}
}
function isAdmin()
{
if (isset($_SESSION['user']) && $_SESSION['user']['user_type'] == 'admin' ) {
return true;
}else{
return false;
}
}
// escape string
function e($val){
global $db;
return mysqli_real_escape_string($db, trim($val));
}
function display_error() {
global $errors;
if (count($errors) > 0){
echo '<div class="error">';
foreach ($errors as $error){
echo $error .'<br>';
}
echo '</div>';
}
}
之类的依赖于void fill(const Rcpp::NumericMatrix& dat) { Rcpp::Rcout << "filling data... " << std::endl; };的方法，因此在声明MyData之前，我必须 Rcpp::NumericMatrix。
我找到了两个解决方案，但是我还没有足够地使用它们来了解是否有任何“陷阱”。
在这里，我将RCPP_EXPOSED_CLASS（）宏用作described by Romain Francois。 （感谢拉尔夫，向我指出了这一点。）
#include <Rcpp.h>此解决方案基于design pattern discussed here。基本上，我只是创建一个指向C ++对象的指针，并使用包装函数来处理它。这是一个看起来可能如何的示例。
#include <Rcpp.h>
class MyData;
class MyModel;
RCPP_EXPOSED_CLASS(MyData)
RCPP_EXPOSED_CLASS(MyModel)
class MyData
{
public:
MyData() = default;
void fill(const Rcpp::NumericMatrix& dat) { Rcpp::Rcout << "filling data... " << std::endl; };
};
class MyModel
{
public:
MyModel() = default;
void train(const MyData& data) { Rcpp::Rcout << "training model... " << std::endl; };
};
// Expose MyData
RCPP_MODULE(MyData){
Rcpp::class_<MyData>("MyData")
.constructor()
.method("fill", &MyData::fill)
;
}
// Expose MyModel
RCPP_MODULE(MyModel){
Rcpp::class_<MyModel>("MyModel")
.constructor()
.method("train", &MyModel::train)
;
}
/***R
myData <- new(MyData)
myModel <- new(MyModel)
myModel$train(myData)
*/
此方法的缺点是AFAIK，没有明显的方法可以检查XPtr指向的对象的类型。例如，对于我来说如何使#include <Rcpp.h>
class MyData
{
public:
MyData() = default;
void fill(const Rcpp::NumericMatrix& dat) { Rcpp::Rcout << "filling data... " << std::endl; };
};
class MyModel
{
public:
MyModel() = default;
void train(const MyData& data) { Rcpp::Rcout << "training model... " << std::endl; };
};
// [[Rcpp::export]]
SEXP make_dataset() {
MyData* datPtr = new MyData();
Rcpp::XPtr<MyData> datXPtr(datPtr);
return datXPtr;
}
// [[Rcpp::export]]
SEXP make_model() {
MyModel* mdlPtr = new MyModel();
Rcpp::XPtr<MyModel> mdlXPtr(mdlPtr);
return mdlXPtr;
}
// [[Rcpp::export]]
void train_model(SEXP mdlXPtr, SEXP datXPtr) {
Rcpp::XPtr<MyModel> mdlPtr(mdlXPtr);
Rcpp::XPtr<MyData> datPtr(datXPtr);
mdlPtr->train(*datPtr);
}
/***R
myData <- make_dataset()
myModel <- make_model()
train_model(myModel, myData)
*/
之类的错误呼叫无效是不明显的。