Connection lost between C++ and Matlab Engine

Question

I have a mission to call Matlab functions from C++ poject. I know there are several ways to do that, I prefer to use it through Matlab Engine.

I have several m-files work perfect in Matlab enviroment.

mymat.m
```
function myfig()
    figure;
end
```

I made a dll-wrapper in C++ to connect the m-files with C++.

dllwrap.h

#pragma once

#include <Engine.h>

#pragma comment  ( lib,"libmx.lib" )
#pragma comment  ( lib,"libmat.lib" )
#pragma comment  ( lib,"libeng.lib" )
#pragma comment  ( lib,"libmex.lib" )

#ifdef DLLWRAP_EXPORTS
#define DLLWRAP_API __declspec(dllexport)
#else
#define DLLWRAP_API __declspec(dllimport)
#endif

DLLWRAP_API bool TestDll();
DLLWRAP_API void MyFigure();

dllwrap.cpp

#include "stdafx.h"
#include "dllwrap.h"

Engine* pEng = NULL;

void StartVirtualEngineMatlab()
{
    if ((pEng = engOpen(NULL)) == NULL)
    {
        MessageBoxA(NULL, (LPSTR)"Can't start MATLAB engine!", (LPSTR) "MatLab Engine: ERROR!", MB_OK | MB_ICONSTOP);
        return;
    };
    return;
}

void StopedVirtualEngineMatlab()
{
    engClose(pEng);
    return;
}

DLLWRAP_API bool TestDll()
{
    if (pEng == NULL) return false;
    return true;
}

DLLWRAP_API void MyFigure()
{
    engEvalString(pEng, "myfig();");
}

dllmain.cpp

#include "stdafx.h"
#include "dllwrap.h"

extern Engine* pEng;

extern void StartVirtualEngineMatlab();
extern void StopedVirtualEngineMatlab();

BOOL APIENTRY DllMain( HMODULE hModule,
                       DWORD  ul_reason_for_call,
                       LPVOID lpReserved
                 )
{
    switch (ul_reason_for_call)
    {
    case DLL_PROCESS_ATTACH:
        StartVirtualEngineMatlab();
        break;
    case DLL_THREAD_ATTACH:
    case DLL_THREAD_DETACH:
    case DLL_PROCESS_DETACH:
        StopedVirtualEngineMatlab();
        break;
    }
    return TRUE;
}

Now I am in focus on a Test project (C# Console Application) to call a m-files through dll-wraper.

Test.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Runtime.InteropServices;

namespace Test
{
    class Program
    {
        [DllImport("dllwrap.dll", CallingConvention = CallingConvention.Cdecl)]
        public static extern bool TestDll();
        [DllImport("dllwrap.dll", CallingConvention = CallingConvention.Cdecl)]
        public static extern void MyFigure();

                static void Main(string[] args)
                {
                    bool res = TestDll();
                    if (res == false)
                        return;

                    MyFigure();
                }
            }
        }

The Test project is running and doing the job, but there is a problem. A Matlab Engine crashes in unexpected time. It may crash at the begining or after a while. I even tried to stop on breaking point right after the engOpen(NULL) function, but the crashing is seems not depending on my break.

I use Visual Studio 2013, Matlab 2015a 32bit. Please help in advise. Thanks.

Okay, so you have a bug in your code. There's nothing we can do to help you without a [testcase](http://stackoverflow.com/help/mcve), beyond suggesting you fire up your debugger and step through the program methodically. — Lightness Races in Orbit, Oct 18 '15 at 12:52

score 0 · Answer 1 · answered Oct 18 '15 at 15:17

Ok, I found the problem. I just removed the line:

StopedVirtualEngineMatlab();

from dllmain.cpp

case DLL_PROCESS_DETACH:
    StopedVirtualEngineMatlab();
    break;
}

and put it as external funtion to call it from the end of the code of Test.cs.

Now it works perfect.

But still I don't understand why the DLL_PROCESS_DETACH case is invoked...?

Connection lost between C++ and Matlab Engine

1 Answers1