Extending a C++ application with embedded scripting

Question

I am developing a C++ application that needs to be multiple platform compatible (Windows/Linux) and want to grant users the ability to extend the software to fit their needs exactly without allowing them to change critical parts of the application (so I do not want them in the C++ code).

What I am looking for is to embed a scripting language (I would prefer Python because I am familiar with it already, but it's not mandatory), so scripts put in some plugin folder can manipulate objects of the application if I want these objects to be modifyable.

The most simple example: if someone wants to build their own UI for my application, they should be able to do so with such a script.

The problem however is, that I've never put C++ and any kind of external scripts together, so I really do not know how to start. After looking for material to get started, I found that Lua claims to be a good language to do that, but I could not find good beginner tutorials.

I would really appreciate if someone knew a good place to start, be it online resources, or a good book. I wouldn't mind spending a few bucks on a good book.

As a learner, I tend to learn best from a mix of example code and a few lines explaining those.

You might be interested in the guide for embedding JavaScript using V8. — jterrace
– jterrace, Commented Jan 15, 2012 at 19:51

jpjacobs · Accepted Answer · 2012-01-16 08:00:41Z

6

I would suggest you to read Programming in Lua, this book has an entire section on how to embed Lua in C (and C++).

It is very highly rated by Amazon users.

The language has also pretty good online documentation and a active mailing list.

edited Jan 16, 2012 at 8:00

jpjacobs

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answered Jan 15, 2012 at 20:01

borges

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1 Comment

nikolas Over a year ago

From what I've been able to look through so far, this book recommendation looks the most promising. I will definitely give it a read. Thanks.

Paul Manta · Accepted Answer · 2012-01-15 20:09:11Z

3

If you want to use Python I would definitely suggest using Boost.Python. It is an incredibly well designed library. Just an example: all you have to do to expose a C++ class to Python is this:

struct World
{
    void set(std::string msg) { this->msg = msg; }
    std::string greet() { return msg; }
    std::string msg;
};

BOOST_PYTHON_MODULE(hello)
{
    class_<World>("World")
        .def("greet", &World::greet)
        .def("set", &World::set)
    ;
}

It handles almost everything automatically: conversions between types, exceptions, it even allows you to use reference counted objects between the two languages with boost::shared_ptr.

answered Jan 15, 2012 at 20:09

Paul Manta

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4 Comments

nikolas Over a year ago

This does sound great, and the Boost documentation looks well written as well. I'll look into it deeper later tonight. Thanks.

Paul Manta Over a year ago

If you're using Visual Studio on Windows it's going to be much easier to install the libraries, just use BoostPro's installer: boostpro.com/download

nikolas Over a year ago

Unfortunately not, I'm working on this project within Debian, using gcc 4.4.5, but thanks for the hint.

sbk Over a year ago

Just so you guys know, there's similar library for Lua called luabind. It is inspired by boost.python and the code to bind classes to Lua with luabind looks almost identical to the one for Python with boost.python

Eric Fortin · Accepted Answer · 2012-01-15 20:03:51Z

The article here at linux journal is a good place to start on how to embed a python interpreter in your c/c++ code. This is only half the battle however because when the interpreter is embedded, you then need to publish some part of your software to the scripting environment. The basic API to do so is in C and if most of your code is C++, it might be best to use boost::python since writing C wrappers around your C++ classes might be cumbersome. You can also use Py++ to generate the boost::python binding.

If you only want to use scripting as a door to customization and you can live with the memory footprint of python, it might be a better choice than Lua. Lua is usually good for small environment like game development. There is also a lot more python developers than lua developers as well as more built-ins and third party libraries available.

guinny · Accepted Answer · 2012-01-15 19:51:46Z

0

for Python, I guess the boost library is meant to do it. As for Lua, I haven't used it myself, but a quick Google search first led me to debian admin and then to Lua's C interface. Have you looked into those?

answered Jan 15, 2012 at 19:51

guinny

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2 Comments

John Zwinck Over a year ago

For Lua there is Luabind, which has roots in Boost Python and works quite similarly (and well).

guinny Over a year ago

thank you very much! I haven't used Lua before and was interested in how I would have started.

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