How to call C++ DLL in C#

Solution 1:

The following code in VS 2012 worked fine:

#include <Windows.h>
extern "C"
{
    __declspec(dllexport) void HelloWorld ()
    {
        MessageBox (0, L"Hello World from DLL!\n", L"Hi",MB_ICONINFORMATION);
    }
    __declspec(dllexport) void ShowMe()
    {
        MessageBox (0, L"How are u?", L"Hi", MB_ICONINFORMATION);
    }
}

NOTE: If I remove the extern "C" I get exception.

Solution 2:

using System;
using System.Runtime.InteropServices;

namespace MyNameSpace
{
    public class MyClass
    {
        [DllImport("DllMain.dll", EntryPoint = "HelloWorld")]
        public static extern void HelloWorld();

        [DllImport("DllMain.dll", EntryPoint = "ShowMe")]
        public static extern void ShowMe();
    }
}

Solution 3:

things that helped:

• The: extern "C" { function declarations here in h file } will disable C++ name encoding. so c# will find the function

• Use __stdcall for the C declaration or CallingConvention.Cdecl in the C# declaration

• maybe use BSTR/_bstr_t as string type and use other vb types. http://support.microsoft.com/kb/177218/EN-US

• download "PInvoke Interop Assistant" https://clrinterop.codeplex.com/releases/view/14120 paste function declaration from .h file in the 3rd tab = c# declaration. replace with dll filename.