Horde3D

I'm trying to call C functions from Lua like this :
But I'm getting the following error :

error C2597: illegal reference to non-static member 'app::envRoot'

You can't access member variables of a class from a static context without an instance of that class.

But how to solve this problem ?! I'm going to have a look at my old C++ book

One solution would be to make all class members static. But in this case you could also use a namespace instead, because a class having only static members does not make really sense, does it?

Whats the advantage of using namespaces or making all of the functions static?

I'm not an expert regarding compilers, so I can't tell you what will be the difference on the generated code, but if you make all members static, I think the result will be nearly the same as if you are using namespaces.

It's more a matter of style/design. If you create a class, one would expect that there could be several instances of this class with all the things classes provide in the context of object orientated programming (like inheritance, etc.). If you are making all members static you don't have those capabilities so IMHO it does not make too much sense to put all those functions into a class.

If you want several instances of a class and use it within lua, you could also pass a pointer of the instance to lua and get it from the stack when calling a lua function. Then you can cast it in your C-lua function and use it. But that's all depending on what you are actually try to do with lua and C++.

I'm using only one instance of app class at whole game. The second way looks amazing too.

EDIT : I've tried to define the envRoot as "static NodeHandle envRoot" but this causes some Linker problems. I want to call app member functions from Lua.

Fixed that problem by changing "static int getNodeHandle()" to "int getNodeHandle()", but I'm getting another error :
And by changing 'app::getNodeHandle' to '&app::getNodeHandle', I'm getting another error :

Because you can't cast class member functions to C functions. Since the methods of a class are bound to the instance of the class, the compiler can't know the address of the function at compile time.

Isn't there anyway to do this? Perhaps you have experienced similar problems when coding the Horde3D Editor. IMHO this will make the Lua too useless when we can't call C functions from Lua easily.

You always need the instance of the class if you want to call pointers of class methods. To solve the lua problem you might want to take a look at the lua bindings within the editor. Doing a google search on lua and c++ might help you also.


You can call C functions from Lua very easily, the problem is that you don't have C functions but C++ class methods.

I've googled a lot about this problem, but couldn't find anything useful. I'll have a look at bindings. Thanks for help

Maybe this helps: http://loadcode.blogspot.com/2007/02/wrapping-c-classes-in-lua.html

Indeed an interesting article