Call C# function from native C++ or C

Question

I'm try to follow this steps: Calling C# from C++, Reverse P/Invoke, Mixed Mode DLLs and C++/CLI 1. I make C# Dll named TestLib:

namespace TestLib
{
    public class TestClass
    {
        public float Add(float a, float b)
        {
            return a + b;
        }
    }
}

2. Then I create C++/CLI Dll named WrapperLib and add reference to C# TestLib.

// WrapperLib.h

#pragma once

using namespace System;
using namespace TestLib;

namespace WrapperLib {

    public class WrapperClass
    {
    float Add(float a, float b)
        {
        TestClass^ pInstance = gcnew TestClass();
        //pInstance
        // TODO: Add your methods for this class here.
        return pInstance->Add(a, b);
        }
    };
}

C+ 3. For check tis example I've create C++/CLI console application and try to call this code:

// ConsoleTest.cpp : main project file.

#include "stdafx.h"

using namespace System;
using namespace WrapperLib;

int main(array<System::String ^> ^args)
{
    Console::WriteLine(L"Hello World");
    WrapperClass cl1 = new WrapperClass();

    return 0;
}

But I get a few errors:

error C2065: 'WrapperClass' : undeclared identifier C:\Projects\TestSolution\ConsoleTest\ConsoleTest.cpp    11  1   ConsoleTest
error C2146: syntax error : missing ';' before identifier 'cl1' C:\Projects\TestSolution\ConsoleTest\ConsoleTest.cpp    11  1   ConsoleTest
error C2065: 'cl1' : undeclared identifier  C:\Projects\TestSolution\ConsoleTest\ConsoleTest.cpp    11  1   ConsoleTest
error C2061: syntax error : identifier 'WrapperClass'   C:\Projects\TestSolution\ConsoleTest\ConsoleTest.cpp    11  1   ConsoleTest

Well I know somewhere I missed, but where?

If the compiler told you "hey, got a few errors, please fix" where would you look first? :) Please tell us what the errors are. — Roman Starkov
– Roman Starkov, Commented Jun 20, 2012 at 13:32
Fixed. I've add VS output. How to right call this function from native C++ or C? — Superjet100
– Superjet100, Commented Jun 20, 2012 at 13:39

Felipe · Accepted Answer · 2012-06-20 14:12:03Z

2

According to @Ben Voigt suggestion I believe that your code should look somewhat like this:

// ConsoleTest.cpp : main project file.

#include "stdafx.h"
#include "WrapperLib.h"

using namespace System;
using namespace WrapperLib;

int main(array<System::String ^> ^args)
{
    float result;
    Console::WriteLine(L"Hello World");
    WrapperClass cl1;

    result = cl1.Add(1, 1);

    return 0;
}

If you don't include the header file of your wrapper library, the C++ compiler will never find its functions and you will keep getting the errors that you displayed earlier.

answered Jun 20, 2012 at 14:12

Felipe

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2 Comments

Superjet100 Over a year ago

My WrapperLib project contain WrapperLib.h with code and WrapperLib.cpp only with: #include "stdafx.h" #include "WrapperLib.h" Is it right?

Felipe Over a year ago

Yes I believe that is correct, however you need to #include your WrapperLib header file into your main project (the one you are using to test it). As @Mark Simith said above, in native C++ it doesn't matter if you did or did not reference another project, you still need to include the header files.

Ben Voigt · Accepted Answer · 2012-06-20 13:39:48Z

1

That's not good C++, looks like Java or C#.

The correct syntax to create a new object in C++/CLI is

WrapperClass cl1;

or

WrapperClass^ cl1 = gcnew WrapperClass();

C++ has stack semantics, you have to tell the compiler whether you want a local object that is automatically disposed at the end of the function (first option), or a handle that can live longer (second option, using ^ and gcnew).

answered Jun 20, 2012 at 13:39

Ben Voigt

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8 Comments

Superjet100 Over a year ago

I try with WrapperClass^ cl1 = gcnew WrapperClass(); but I get errors: Error 1 error C2065: 'WrapperClass' : undeclared identifier error C2065: 'cl1' : undeclared identifier error C2061: syntax error : identifier 'WrapperClass'

Ben Voigt Over a year ago

@Superjet100: You also need #include "WrapperLib.h"

Superjet100 Over a year ago

But in this test console aplication I don't have #include "WrapperLib.h"

Ben Voigt Over a year ago

@Superjet100: Oh, it's a separate project? Then add a reference to the project where WrapperLib::WrapperClass is defined.

Matt Smith Over a year ago

For native classes from another dll (like WrapperClass), to make them visible in your translation unit you need to #include their header file (just like standard C++ code). For managed classes from another dll, you only need to add a reference to the project (just like in C#).

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