SWIG for Lua: Class demonstration

In this entry, we demonstrate how to expose a C++ class to Lua using SWIG. The environment I use is Ubuntu 16.04.

First, we define the C++ class in example.hpp:

	class MyClass
	{
	public:
	MyClass(int a, int b);
	void greet();
	private:
	int x;
	int y;
	};

view raw example.hpp hosted with ❤ by GitHub

The class implementation is defined in example.cpp:

	#include <example.hpp>
	#include <ctime>
	#include <cstdio>
	MyClass::MyClass(int a, int b): x(a), y(b) {}
	void MyClass::greet()
	{
	printf("Hello, world: x=%d y=%d\n", x, y);
	}

view raw example.cpp hosted with ❤ by GitHub

Then, we define the interface file, example.i, to be used by SWIG:

	%module example
	%{
	/* Includes the header in the wrapper code */
	#include "example.hpp"
	%}
	/* Parse the header file to generate wrappers */
	%include "example.hpp"

view raw example.i hosted with ❤ by GitHub

We then use SWIG to generate the wrapper file, example_wrap.cxx:

% swig -lua -c++ example.i

Next, we compile the C++ source files:

% g++ -fPIC -I/usr/include/lua5.2 -c example_wrap.cxx -o example_wrap.o
% g++ -fPIC -I. -c example.cpp -o example.o

Then, we create the shared object, example.so:

% g++ -shared -I/usr/include/lua5.2 example_wrap.o example.o -o example.so

We write a Lua script to test if SWIG works:

	#!/usr/bin/lua
	package.loadlib('./example.so', 'luaopen_example')()
	A = example.MyClass(6, 7)
	A:greet()

view raw test.lua hosted with ❤ by GitHub

When run:

% ./test.lua
Hello, world: x=6 y=7

Hope this helps the world.