How to Develop a C++ DLL for R in Visual Studio 2015

The programming language R is great for statistics and analysis. R is becoming more and more relevant for business analysis. Microsoft has already integrated R in SQL Server 2016, Power BI and offers an open source R Implementation and Visual Studio integration. There are many tutorials for C interop with R but most of them use Linux tools and not Visual C++. This is a walkthrough how to build a C++ DLL and use it in R all in Visual Studio.

    Visual C++
      Create a new empty solution in Visual Studio. Add a new Visual C++ Win32 project.

image

In the C++ Application dialog, choose a DLL

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A new C++ project is created include a header file and a C++ file.

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Open the stdafx.h file and add the definition for function foo() in the header file.

// stdafx.h : include file for standard system include files,
// or project specific include files that are used frequently, but
// are changed infrequently
//

#pragma once

#include “targetver.h”

#define WIN32_LEAN_AND_MEAN             // Exclude rarely-used stuff from Windows headers
// Windows Header Files:
#include <windows.h>

 

/// export symbols for DLL and specify C naming conventions

extern “C” __declspec(dllexport) void __cdecl foo(double *in, double *out);

Open the .cpp file and add the following implementation.

void foo(double *in, double *out)
{
double value = in[0] * 2;
out[0] = value;
}

Make sure to change the architecture to x64 before building.

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Build the solution. The resulting DLL will be outputed in the x64 folder in the project folder(!) not in the Debug folder where a C# DLL would be.

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R Project

Add a new R project to  the solution which already contains the C++ project. Go to the R Interactive Window.

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Load the DLL from your output directory.

dyn.load(“C:\\PATH_TO\\YOUR.DLL”)

Declare 2 variables for input and output and assign values. For example input value 21 and a default value 0 for the output variable. Call the DLL function and output the result

value_in <- 21
value_out <-0
.C(“foo”,as.double(value_in),result=as.double(value_out))$result

The result should look like this

image

About erpcoder
Software Engineer and Dynamics AX enthusiast working in Research & Development for InsideAx

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