These are several tips and tricks collected from the web, during my first steps towards a better understanding of the C, C++ and C# programming languages.

Generate a shared library from a C program

To generate a shared library you need first to compile your C code with the -fPIC (position independent code) flag.

gcc -c -fPIC hello.c -o hello.o

This will generate an object file (.o), now you take it and create the .so file:

gcc hello.o -shared -o libhello.so

To do it in one step you can use

gcc -shared -o libhello.so -fPIC hello.c

You could add -Wall to get all warnings, and -g to get debugging information, to your gcc commands.

Source

How to call a C function from C#

Create a C file, say libtest.c with some content (e.g. a simple pseudo-wrapper for printf):

#include <stdio.h>

void print(const char *message)
{
  printf("%s\n", message);
}

Then create the shared library libtest.so. Finally use your library in C#:

using System;

using System.Runtime.InteropServices;

public class Tester
{
        [DllImport("libtest.so", EntryPoint="print")]

        static extern void print(string message);

        public static void Main(string[] args)
        {

                print("Hello World C# => C++");
        }
}

In case of a System.DllNotFoundException just add the current directory to the library path:

export LD_LIBRARY_PATH=pwd

Source