On Wed, Oct 25, 2006 at 06:18:07PM +0200, Matthias Isele wrote:
Hi everybody,
I've got a lua problem.
There are two c/c++ structs:
typedef struct structA
{
int a;
int b;
};
typedef struct structB;
{
int x;
int y;
structA anotherStruct;
};
I can access any struct element in lua with the following notation:
structA.a = 1
structA.b = 2
and
structB.x = 3
structB.y = 4
Until here everything works fine.
Now the tricky part (and also my question):
how can I access the structB in structA in a notation like:
structB.anotherStruct.a = 5 in lua.
Here's how I implemented the structs:
I think you posted the wrong code, it's the code for structB thats
important, particularly the call to lua_newuserdata().
Exactly how to do this depends on how you use these user-datas, but
I think basically what you need to do is return a userdata
proxy = structB.anotherStruct
proxy.a = 3
proxy needs to not have a pointer to the structB memory, but instead
have a lua reference, so that it can look B up, and set the correct
struct elements, have you seen http://www.lua.org/pil/27.3.2.html?
It might be possible to change things so what I call "proxy" above
is the same as the structA wrapper, except that it would operate in
two modes, one it "owned" the memory, the other it just had a pointer
to another object.
Hope that helps a bit, and didn't just repeat stuff you knew.
Also, if you don't actually need to keep the C struct around as memory,
another option might be to just represent it in lua as tables. pseudo-C code:
void create_from_structB(lua_State* L, struct structB* b)
{
lua_newtable(L)
// do table.a = b->structA.a, I probably have this code all wrong,
// its from memory
lua_push(L, "a");
lua_push(L, b->structA.a)
lua_settable(L, -3);
// again for "b"
lua_newtable(L) // the table for B
// set x to b->x
// set y to b->y
// anotherStruct to the first table created above
}
There are a few times where I've made user-data, then though, why? I can
represent this data as tables in lua, so they everything tables do
already. Then if they are passed as args to C functions, those C
functions can convert the tables back into the underlying C data
structers, as necessary. This also allows things like:
b = StructB.new{
x = 1,
y = 2,
anotherStruct = {
a = 4,
b = 5,
}
}
Cheers,
Sam
