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On Apr 9, 2008, at 9:42 PM, Alex Davies wrote:

----- Original Message ----- From: "Eugen-Andrei Gavriloaie"

The table might have keys 1,2,3,55,34,22,"sdfds",etc. This table is returned by calling a lua function (is on the C++ stack). After doing some c++ processing I'd like to add more "anonymous" values (with no keys) to the table and pass it as a parameter to anoter lua function. So, I have no guarantee that the key is not in use. :(

Um, just so we're clear, the table: {1, 2, 3, 55, 34, 22}
does not have any "anonymous" values. It's merely a short hand way of writing:
{ [1] = 1, [2] = 2, [3] = 3, [4] = 55, [5] = 34, [6] = 22 }
As in Lua there is no such thing as a value in a table without a key.
Yes you are right. But here is an example of an unwanted value overwrite: 1. Lua calls a c++ with the following argument: {"first_anon_value","second_anon_value",false,22}. I know that internally this table is represented like this:
	1=> first_anon_value
	2=> second_anon_value
	3=> false
	4=> 22
1,2,3 and 4 key values are computed by lua internally (I really don't know the algorithm behind the scene)

2. the c++ function is making some computing and decide that row number 2 must be deleted. So, internal representation is now like this:
	1=> first_anon_value
	3=> false
	4=> 22

3. We now try to add a new value using your method. Let this value be the string "this is a string". lua_objlen(L, -2) + 1 evaluates to 4 in this case.
I think (not sure) that after lua_rawset the table will look like this:
	1=> first_anon_value
	3=> false
	4=> this is a string
As you can see 22 was overwritten with "this is a string".

Extract from the docs:

--begin cut--

[-1, +0, m]

void lua_rawseti (lua_State *L, int index, int n);

Does the equivalent of t[n] = v, where t is the value at the given valid index and v is the value at the top of the stack.

This function pops the value from the stack. The assignment is raw; that is, it does not invoke metamethods.
--end cut--

So the question is: n denotes a position or a key?

How would you retrieve such a value?

(Your wording was a little vague).

So to add more values, simply use the code provided earlier (lua_rawseti(L, -2, lua_objlen(L, -2) + 1)). See, t[#t+1] is always nil, by definition. So you're always safe to add more values there.

(If you mean that want you want a way of attaching additional info to a table without modifying the table in anyway, that's a separate problem that can be solved by weak tables).

- Alex