How to call C++ DLL in C#

Question

I have written a DLL in dev C++. The DLL's name is "DllMain.dll" and it contains two functions: HelloWorld and ShowMe. The header file looks like this:

DLLIMPORT  void HelloWorld(); DLLIMPORT void ShowMe(); 

And the source file looks like this:

DLLIMPORT void HelloWorld () {   MessageBox (0, "Hello World from DLL!\n", "Hi",MB_ICONINFORMATION); }  DLLIMPORT void ShowMe() {  MessageBox (0, "How are u?", "Hi", MB_ICONINFORMATION); } 

I compile the code into a DLL and call the two functions from C#. The C# code looks like this:

[DllImport("DllMain.dll", CallingConvention = CallingConvention.Cdecl)] public static extern void HelloWorld();  [DllImport("DllMain.dll", CallingConvention = CallingConvention.Cdecl)] public static extern void ShowMe(); 

When I call the function "HelloWorld" it runs well and pops up a messageBox, but when I call the function ShowMe an EntryPointNotFoundException occurs. How do I avoid this exception? Do I need to add extern "C" in the header file?

Answer 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.

Answer 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();     } }