Integrating a script language into a C++ application

Question

I'm really new to C++ and I've come across a problem I've not been able to solve by reading documentations.

I want to embed a script language into my c++ application. That language could be javascript, lua or preferably python.

I'm not looking for something like Boost.Python / swig, something that is able to wrap my c++ functions / classes to a python interface, but rather a python_evaluate_and_return_result_as_variable("my_code"); function.

I have a whole bunch of structs containing a few integers:

struct my_integers {
    int a;
    int b;
    int c;
    int d;
    int e;
};

Now I want to do some math with these integers, for example:

i.a = i.c * i.e;

The math I want to do will be changing a lot in the future and I need people other then me be able to change the math without having access to the c++ code.

I'm thinking about a code structure like this:

I initialize my struct and fill it with the starting values
I load an external python function, lets say "my_python_function", that takes the struct as an argument and does so math with it before returning it.
I get my struct like i = my_python_function_cppwrapper(i)

Is something like that possible? I googled a lot for this but the only thing I seem to find are wrappers that provide c++ -> python (or the other way around) functionallity without really interacting with variables.

I'd be really thankful for any help,
Robin.

Why not Boost.Python? It works and will let you do exactly what you want. — wilx, Sep 23 '10 at 16:43

score 8 · Answer 1 · answered Sep 23 '10 at 16:25

8

The Python documentation has a page on embedding Python in a C or C++ application.

answered Sep 23 '10 at 16:25

Jon Purdy

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score 8 · Accepted Answer · answered Sep 23 '10 at 16:37

8

Why not use Boost.Python? You can expose your data classes to Python and execute a script/function as described here.

answered Sep 23 '10 at 16:37

David Feurle

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Thank you very much, that was what I've been looking for. I must've missed the section when I looked over Boost.Python. – Robin Sep 24 '10 at 07:27

score 6 · Answer 3 · answered Sep 23 '10 at 16:25

6

If you want to simply run Python scripts from C/C++, then use the Python C API. In your C/C++ code:

PyRun_SimpleString("import math; x = math.sqrt(2 * 2)");

For more complicated things, you will have to look at the API docs, but it's pretty straightforward.

answered Sep 23 '10 at 16:25

Ross Light

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That doesn't quite work for me as I need to pass and extract variables, but thanks for your comment :) – Robin Sep 24 '10 at 07:27

score 2 · Answer 4 · answered Sep 23 '10 at 16:21

2

How about embedding a JavaScript engine, such as V8?

answered Sep 23 '10 at 16:21

Matthijs Bierman

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I think I'm sticking with python but I may use V8 in my next project. Thanks for the hint, the only javascript engine I could think about was spidermonkey. – Robin Sep 24 '10 at 07:28

score 1 · Answer 5 · answered Sep 23 '10 at 16:44

1

dont forget the grand-daddy of embedded scripting language - tcl.

tcl has v nice c++ wrapper (modelled on boost.python) that makes it trivial to invoke and to wire up callbacks to your code

answered Sep 23 '10 at 16:44

pm100

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score 1 · Answer 6 · answered Sep 23 '10 at 16:48

Lua works pretty well too, especially since its small, is ansi c compliant, has a low memory foot print along with a great wiki and messaging list. If you need even more speed there is a x86 32 and 64 bit jit version(luajit). Binding can be done with an array of tools/libraries, like swig or lunar(the wiki lists them all). The only problem that i can see is binding the struct members so they can be referenced directly(ie: struct.member = 4), though its possible to set this up with metatables that have get and set methods bound to variable names

score 1 · Answer 7 · answered Sep 23 '10 at 17:00

You say that you're not looking for something to wrap your C++ functions / classes in a Python interface, but if you want Python code to be able to refer to members of your C++ my_integers structure, that is wrapping C++ classes in a Python interface. Of course, you're free to wrap as many or as few classes as you want - in this example, you'd wrap my_integers, then you'd embed a Python interpreter to do stuff with my_integers.

score 1 · Answer 8 · answered Sep 23 '10 at 17:50

1

For something as simple as you describe, you could implement an interpreter for your own 'little language'. You could even call it the "Robin" language. ;-)

answered Sep 23 '10 at 17:50

martineau

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score 1 · Answer 9 · answered Sep 23 '10 at 17:56

I advice using Lua as internal scripting engine. Implementation is just a few lines, and though light, the language has sufficient power. So no need for TCL. You might as well look at python, integration in C++ is rather easy, as there exists a Boost.Python implementation facilitating integration.

But depending on the application, I'd still recommend Lua.

Integrating a script language into a C++ application

9 Answers9