Re: Calling from C through lua to another C function

[Mildred <ml.mildred593@...>]

On Sun, 30 Apr 2006 10:57:12 -0700 (PDT) Steve Heller wrote:
> I know this is possible, but I've been unable to
> figure out exactly how to do it. Does anyone have a
> complete example that actually compiles and runs? It
> doesn't have to be anything fancy; just passing a
> light user data value from C through lua back to C
> will do the job.

What's wrong with the manual ?

int create_pointer(lua_State* L) {
	mytype* p = NULL;
	lua_pushlightuserdata(L, (void*) p);
	return 1; // the userdata
}

int access_pointer(lua_State* L) {
	luaL_checkany(L, 1);
	mytype* p = (mytype*) lua_touserdata (L, 1);
	return 0;
}

Is that what you want ?

Not tested but should work.
I suggest you to use full userdata because these can be garbage
collected (and so let you free memory) and assigned to metatables. If
you use full userdata, you must then deal with mytype**

Example:

int create_pointer(lua_State* L) {
	mytype** p = lua_newuserdata(L, sizeof(mytype*));
	*p = NULL;
	{ // optional
		if(luaL_newmetatable(L, "metatable_unique_name")) {
			// the metatable isn't created yet
			// it is pushed on the stack, populate it
		}
		// STACK: userdata, metatable
		lua_setmetatable(L, -2);
		// STACK: userdata
	}
	return 1; // the userdata
}

int access_pointer(lua_State* L) {
	mytype* p = *((mytype**)
		luaL_checkudata(L, 1, "metatable_unique_name"));
	// do what you want with p here
	return 0;
}

Not tested but should work :)

Mildred

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