How to call dll file created with c# from c++ project?

Question

I have a dll file which is created in the c# language.And I wanted to use the functions which are written in c# language in that dll file from a c++ project. I know it's possible to use c# dll with c# project. But no idea of what is the best way of doing c# dll in c++ project. I'm using visual studio 2013. All your guidance are highly appreciate.

Answer 1

I'll summarize the basic steps to take to expose a C# class to C++ through COM. Let's say you have the following C# class:

public class Number
{
    public Number()
    {
    }

    public int Value
    {
        get;
        set;
    }
}

First you need to create an interface for the class to implement. Only the methods and properties exposed through that interface are visible to COM (and therefore C++). Typically this interface has the same name as the class, but with an "I" prefix:

public interface INumber
{
    int Value
    {
        get;
        set;
    }
}

Next you need to add the ComVisible and Guid attributes to both the interface and the class. It's also recommended to add [ClassInterface(ClassInterfaceType.None)] to the class:

[ComVisible(true)]
[Guid("71CACDF6-B6CD-4A46-B951-02E5C542852C")]
public interface INumber
{
    ...

[ComVisible(true)]
[Guid("B5809A32-A066-42E3-96D7-09FE622BC994")]
[ClassInterface(ClassInterfaceType.None)]
public class Number : INumber
{
    ...

(I got the GUIDs by using the GUID utility that comes with Visual Studio. You can find it at C:\Program Files (x86)\Microsoft Visual Studio 12.0\Common7\Tools)

That's it for the C# side. After you build the C# DLL, you need to register it with COM by using the Regasm.exe command-line utility. Start the command prompt and type the following commands:

"C:\Program Files (x86)\Microsoft Visual Studio 12.0\Common7\Tools\vsvars32"

Regasm ExampleDLL.dll /codebase /tlb

(You may need to modify the first one if your VS installation path is different.)

Now you can use the DLL from C++ like this:

#include <iostream>
#import "ExampleDLL.tlb" // This is a file that should have been generated by Regasm.exe

using namespace std;
using namespace ExampleDLL;

int main()
{
    CoInitialize(NULL);

    INumberPtr pNumber;
    pNumber.CreateInstace(__uuidof(Number));
    pNumber->Value = 5;
    cout << pNumber->Value;

    return 0;
}

For more details, see Exposing .NET Framework Components to COM.