从 C# 应用程序调用 c++ DLL

Question

I have C# as my front end application and I want to call c++ dll from my c# but I am getting error. I am posting my code here please help me out how to resolve this:

Program.cs

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

namespace TestCSharp
{
     class Program
     {
          [DllImport("C:\\Users\\xyz\\source\\repos\\Project1\\Debug\\TestCpp.dll", CallingConvention = CallingConvention.Cdecl)]
          public static extern void DisplayHelloFromDLL(StringBuilder name, int appId);

          static void Main(string[] args)
          {
               try
               {
                   StringBuilder str = new StringBuilder("name");                
                   DisplayHelloFromDLL(str, str.Length);
                   str.Clear();
               }
               catch(DllNotFoundException exception)
               {
                    Console.WriteLine(exception.Message);
               }
               catch(Exception exception)
               {
                   Console.WriteLine("General exception " + exception.Message);
               }
               finally
               {
                   Console.WriteLine("Try again");
               }
          }
     }
 }

and cpp code like below:

Header: source.h

#include <string>
using namespace std;

extern "C"
{
    namespace Test
    {
        class test
        {
        public:
            test();
            __declspec(dllexport) void DisplayHelloFromDLL(char * name, int appId);
        }
    }
}

c++ class: source.cpp

#include <stdio.h>
#include "source.h"

Test::test::test()
{
    printf("This is default constructor");
}
void Test::test::DisplayHelloFromDLL(char * name, int appId)
{
    printf("Hello from DLL !\n");
    printf("Name is %s\n", name);
    printf("Length is %d \n", appId);
}

Code is building successfully but when I run this I got Unable to find an entry point named 'DisplayHelloFromDLL' in DLL.

Same CPP code when I am writing without using namespace and class, it is working fine. ie

Header: source.h

extern "C"
{
    __declspec(dllexport) void DisplayHelloFromDLL(char * name, int appId);
}

c++ class: source.cpp

#include "source.h"

void DisplayHelloFromDLL(char * name, int appId)
{
    printf("Hello from DLL !\n");
    printf("Name is %s\n", name);
    printf("Length is %d \n", appId);
}

So how do I use DLL which has namespaces and claases in my c# application.

Answer 1

Thanks for the answers. I resolved the issue by making one extra class(Wrapper class) that contains the managed code. This wrapper class is called by the c# classes in the same way as I mentioned in the question. This wrapper class than call the c++ class and return the result to the UI.

Answer 2

The easiest way is to create a "proxy": set of clear-C functions, these will call your c++ functions. I think calling c++ function is not good idea: name decoration is changed from version to version of compiler.

Answer 3

Do you have this project hosted somewhere? On the first view I would say that you need to build the c++ project first (only the c++.:!) and then run the C# project. Perhaps you would like to have a look here: Testprojects Especially the "MessageBox" stuff shows how to use C++ with C#. There are some Testprojects with UWP as well.