Creating a DLL using C++
For creating a DLL in C++, I was used cl.exe, which comes with .net framework. For the implementation I just wrote simple C++ file.(Simple.cpp)

#include <iostream>

extern "C" __declspec(dllexport) char* Hello();
char* Hello()
{
	return "Hello world";
}

I think this is pretty much clear.The extern “C” __declspec(dllexport) allows generate export names automatically. For more details :Exporting from a DLL Using __declspec(dllexport)(MSDN)

After creating this Simple.cpp file, go to Visual Studio Tools > Visual Studio 2008 Command Prompt. Go to the location where you have stored the Simple.cpp file and for compiling and linking C++ file you can use “cl.exe /LD Simple.cpp”.(For more details about cl.exe options checkout : Compiler Options Listed Alphabetically(MSDN) It will compile and Link, and gives a DLL as output.

Consuming a C++ library in C#
When I try to add the DLL by Add Reference, Visual Studio will not allows to add C++ library as Reference. So I tried it with Interop option, by using DLLImportAttribute.

[DllImport(@"D:\Simple.dll", EntryPoint = "Hello")]
public extern static string Hello();

Then you can call this function in C# like the following

private void button1_Click(object sender, EventArgs e)
{
            MessageBox.Show(Hello());
}

It will display a Messagebox with “Hello World”. Thats it you consumed a C++ DLL in C#.

Issue in the implementation

1. I can’t use the DllImport function without the full location. To avoid this I tried to Register the DLL using RegSvr32.But I got some error from RegSvr like this.

The module “D:\Simple.dll” was loaded but the entry-point DllRegisterServer was not found.

Make sure that “D:\Simple.dll” is a valid DLL or OCX file and then try again.

I still exploring the things, I will update once I got the solution for this. Happy Coding