Wrapping a C# DLL with COM Interface to be Called by C++ in VS2015

Step 1 – Run Visual Studio 2015.

Step 2 – Create a ‘Class Library’ project in VS2015.

Step 3 – Right click project -> Properties -> Build -> Select ‘Register for COM Interop’

Step 4 – Create a class file in which you would put the COM interface and class.

Step 5 – Using the following namespace in your class file.

using System.Runtime.InteropServices;

Step 6 – Create an interface and set the following attribute.

[ComVisible(true)]

Step 7 – Generate GUID attribute for the interface using the ‘Generate GUID’ tool.

Step 8 – Add a new class which implements the interface just created. Add the 2 attributes below to the class.

[ComVisible(true)]
[ClassInterface(ClassInterfaceType.None)]

Step 9 – Generate GUID for the class.

Step 10 – Implement the function in the class.

Step 11 – Set [ComVisible(true)] in AssemblyInfo.cs

Step 12 – Build the project. A tlb file and a dll file would be generated.

Step 13 – Open your C++ project.

Step 14 – Put the tlb file in the project folder. Add the import code like below. After building your C++ project, a tlh file would be generated.

import “xxx.tlb”

Step 15 – Don’t forget to use the namespace you created in the C# dll. Myself always forget this.

Step 16 – Adding the codes in your C++ project like below.

CoInitialize(NULL);
interfaceInCSharp p(__uuidof(classInCSharp));
_bstr_t pt = p->functionInCSharp( );
CoUninitialize();

Step 17 – Use REGASM.exe to register C# dll.