DotNet andd C++ example

DotnetAndCPP.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
+  </PropertyGroup>
+
+</Project>

Libs/CMakeLists.txt

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+cmake_minimum_required (VERSION 3.10)
+
+project (TestExample CXX)
+
+set (SOURCES
+    src/Arithmetic.cpp
+    src/Entry.cpp)
+
+set (HEADERS
+    include/Arithmetic.h)
+
+add_library(TestExample SHARED ${SOURCES} ${HEADERS})
+include_directories(include)

Libs/include/Arithmetic.h

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+#ifndef ARITHMETIC_H_
+#define ARITHMETIC_H_
+
+class Arithmetic {
+public:
+    Arithmetic() = default;
+
+    int add(const int, const int);
+};
+
+#endif

Libs/src/Arithmetic.cpp

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+#include "Arithmetic.h"
+
+int Arithmetic::add(const int a, const int b) {
+    return a + b;
+}

Libs/src/Entry.cpp

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+#include "Arithmetic.h"
+
+
+extern "C" {
+int add(int, int);
+
+
+int add(int a, int b) {
+    Arithmetic matics;
+
+    return matics.add(a, b);
+}
+}

Program.cs

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+using System;
+using System.Runtime.InteropServices;
+
+namespace DotnetAndCPP
+{
+    class Program
+    {
+        static void Main(string[] args)
+        {
+	    var a = 54;
+	    var b = 23;
+
+	    var result = add(a, b);
+
+	    Console.WriteLine($"a: {a} + b: {b} = {result}");
+        }
+
+	[DllImport("libTestExample.so")]
+	public static extern int add(int a, int b);
+    }
+}

README.md

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+Quick test on how to dip into C/C++ from C# using your own shared C++ libraries
+
+
+# Building
+Building and testing is quite quick and only involves several steps. Before proceeding, it should be noted that this quick test targets Linux. This makes a difference because in Linux C++ shared libraries have a *.so file extension compared to Windows having a *.dll file extension. The ``Program.cs`` file is looking for a shared library with an extension ending is *.so. As is this test will not work on Windows without some modifications.
+
+### Required
+* Linux
+* .NET Core 3.1
+* GCC >= 7 or clang >= 7
+
+## Building C++ library
+1. Change into the C++ Libs directory and create a build directory
+```Bash
+cd Libs; mkdir build
+```
+2. Build the C++ library
+```Bash
+cd build; cmake -DCMAKE_BUILD_TYPE=DEBUG ..; make
+```
+3. Copy the library to the root of the project
+```Bash
+cp libTestExample.so ../../
+```
+
+## Building .NET console software
+1. Ensure that you are in the root of the project. Then build the software
+```Bash
+dotnet build
+```
+2. Copy the C++ library to where the executable is build
+```Bash
+cp libTestExample.so bin/Debug/netcoreapp3.1/
+```
+3. Run the software
+```Bash
+dotnet run
+```
+4. The .NET code is calling a function from the C++ library that was built. The result is the sum of two integers