Compiling and running SWIG for Lua in Ubuntu 16.04 using C++

This blog entry is quite similar to my previous entry. The difference is that this entry uses C++ source files instead of C.

We first start with the C++ header file:

	extern double My_variable;
	int fact(int n);
	int my_mod(int x, int y);
	char *get_time();

view raw example.hpp hosted with ❤ by GitHub

Notice the use of extern for the declaration of the global variable, since we are dealing with C++ here and not C.

We then create the C++ implementation file:

	#include <example.hpp>
	#include <ctime>
	double My_variable = 3.0;
	int fact(int n) {
	if (n <= 1) return 1;
	else return n*fact(n-1);
	}
	int my_mod(int x, int y) {
	return (x%y);
	}
	char *get_time()
	{
	time_t ltime;
	time(&ltime);
	return ctime(&ltime);
	}

view raw example.cpp hosted with ❤ by GitHub

Then we create the interface file for 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 call SWIG to generate the wrapper file:

% swig -lua -c++ example.i

Notice the use of the -c++ argument.

Next, we compile the wrapper file:

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

Notice that the generated wrapper file has the file suffice .cxx

We then compile the C++ implementation file:

% g++ -fPIC -I. -c example.cpp -o example.o

Finally, we create the shared object to be used by our Lua script:

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

We write a Lua script for testing:

	package.loadlib('./example.so', 'luaopen_example')()
	print(example.My_variable)
	print(example.fact(5))
	print(example.my_mod(5, 3))
	print(example.get_time())

view raw test.lua hosted with ❤ by GitHub

When run:

% lua test.lua
3
120
2
Wed Jun 14 16:41:11 2017

Hope this helps the world. :)