Create nested tables from C

Question

I'm trying to create this datastructure from C:

local table = {
    id = 12,
    items = {
        {
            id = 1,
            name = "foo",
        },{
            id = 2,
            name = "bar",
        }
    }
}

However I don't manage to get the anonymous tables working. (It's an array I want but array and tables is the same in lua afaik).

lua_newtable(L);
lua_pushinteger(L, 1);
lua_setfield(L, -2, "id");
lua_newtable(L);
lua_newtable(L);
lua_pushinteger(L, 1);
lua_setfield(L, -2, "id");
lua_pushstring(L, "foo");
lua_setfield(L, -2, "name");
lua_setfield(L, -2, "1");

lua_newtable(L);
lua_pushinteger(L, 1);
lua_setfield(L, -2, "id");
lua_pushstring(L, "bar");
lua_setfield(L, -2, "name");
lua_setfield(L, -2, "2");
lua_setfield(L, -2, "items");

And this gives

{
  id = 1,
  items = {
    ["1"] = {
      id = 1,
      name = "foo"
    },
    ["2"] = {
      id = 1,
      name = "bar"
    }
  }
}

I'm using lua 5.1 so I don't have access to lua_seti

How does it not work precisely? You are probably attempting to set an array item with lua_setfield. Use lua_seti instead. — Nick Zavaritsky, Mar 08 '22 at 10:42

score 2 · Accepted Answer · answered Mar 08 '22 at 11:39

As previously mentioned, a table and an array is the same data structure in Lua. In order to “set an array item” it is paramount to use a number as a key. One can’t set an array item with lua_setfield as it uses string keys. From the output we can see that the function worked exactly as advertised - items were inserted into the table under string keys “1” and “2”.

Please use lua_settable.

void lua_settable (lua_State *L, int index); Does the equivalent to t[k] = v, where t is the value at the given valid index, v is the value at the top of the stack, and k is the value just below the top.

Use lua_pushnumber to push the desired index into the stack, to be used as the key by lua_settable.

Create nested tables from C

1 Answers1