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Asked: 2026-05-11T19:07:12+00:00

I’m trying to write some c++ classes for interfacing with LUA and I am

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I’m trying to write some c++ classes for interfacing with LUA and I am confused about the following:

In the following example: Wherigo.ZCommand returns a “Command” objects, also zcharacterFisherman.Commands is an array of Command objects:

With the following LUA code, I understand it and it works by properly (luaL_getn returns 3 in the zcharacterFisherman.Commands c++ set newindex function):

zcharacterFisherman.Commands = {
  Wherigo.ZCommand{a="Talk", b=false, d=true, c="Nothing available"},
  Wherigo.ZCommand{a="Talk", b=false, d=true, c="Nothing available"},
  Wherigo.ZCommand{a="Talk", b=false, d=true, c="Nothing available"},
}

But when the array is defined with the following LUA code with a slightly different syntax luaL_getn returns 0.

zcharacterFisherman.Commands = {
  Talk = Wherigo.ZCommand{a="Talk", b=false, d=true, c="Nothing available"},
  Talk2 = Wherigo.ZCommand{a="Talk", b=false, d=true, c="Nothing available"},
  Talk3 = Wherigo.ZCommand{a="Talk", b=false, d=true, c="Nothing available"},
}

All objects are defined in c++ and the c++ objects hold all the object members so I am trying to just connect LUA to those c++ objects. Is this enough or do I need to post some of my code??

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1 Answer

  1. Editorial Team

    luaL_getn is for getting the highest numeric element of an array in Lua. An array is a table with only integer indices. When you define a table in Lua (the first example) without explicitly setting indices, you will get an array with elements 1, 2, and 3. Naturally, luaL_getn returns a 3 here. luaL_getn is NOT defined to return the number of elements in the table, it is defined to return the highest numeric index in the table (see http://www.lua.org/manual/5.1/manual.html#pdf-table.maxn)

    The second example is NOT using numeric indices, and this table is not a Lua array — it is more like a hash table. Since luaL_getn only works on true arrays, you wouldn’t expect it to work here.

    Unfortunately, there is no simple way to get the number of elements in a table (lua_objlen solves a related problem, but does not fix this one). The only way to do it is to either:

    1. Always use array notation. Don’t ever use anything else as the keys in your table. You will get a lot of speed-ups this way.
    2. Iterate through your table and count the number of elements when you wish to know the table’s size. The language does not provide a one-line method for getting the size of a full table, since general tables are implemented using hashes and do not track their element count.
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