Re: SWIG/Lua/C++ object instance

["mark gossage " <mark@...>]

Hello Joey,

I do almost all my SWIG-LUA work from the lua side. Swig is really good for just wrappering up a C/C++ library to get it readable by lua. Getting the C++ to talk to lua is fairly easy, but not well documented.

You idea of lua_pushlightuserdata(), was close, but not there.
You probably want something like this:

Foo* p= new Foo();
SWIG_NewPointerObj(L,p,SWIGTYPE_p_Foo,1);
lua_setglobal (L, "p");

The SWIG_NewPointerObj() creates a userdata (not a lightuserdata) for the foo object & pushes it to the stack. The last param (in this case 1) is whether you want lua to manage the memory (0 for no, 1 for yes).

The SWIG_NewPointerObj() and SWIGTYPE_p_Foo are both found in the wrapping file.

Once you have that you should be able to do in lua:
print(p)
print(swig_type(p))
p:some_function()

Let me know if you have any other questions.
Regards,
Mark

> I create an instance of my class variable in C++ and want to use Lua  
> to use some of the routines in my C++ class so I used SWIG to  
> generate the bindings for Lua and I think I have that right.
> 
> However, I can not figure out how to make Lua use my C++ variable  
> instance instead of creating a new one.  I was looking at the Wiki  
> and I am very close to the CppObjectBinding method, except I am using  
> SWIG.
> 
> I have a :
> 
>      lua_pushlightuserdata (global_Lua_state, this);
>      lua_setglobal (global_Lua_state, "this");
> 
> to put the "this" pointer on the stack.  I want to interface that 
> 
> with Lua:
> 
> 
> print ("In the Lua script")
> b = plot.Plot(this)  -- wrong!  How do I make b = this, but be of a  
> plot.Plot () type.
> print (this)
> print (b)
> print (b:DumpV (0))
> print (this:DumpV(0))
> 
> Two addresses are printed out, but they are different (which I  
> expect).  I want to do this:DumpV (0), but I get a:
> 
> In the Lua script
> userdata: bc4dd8
> userdata: b53330
> dump.lua:7: attempt to index global 'this' (a userdata value)
> 
> I feel I am missing something simple, but I just can't get the next  
> step.  I feel like if I go to the direct way of binding like in the  
> wiki CppObjectBinding, I can get this to work, but then I have to do  
> all the bindings myself so I would like to stick with SWIG.
> 
> Thanks for any ideas!
> 
> Joey