Re: finding length of a table

["Matthew M. Burke" <matthew@...>]

Hans van der Meer wrote:
> Trying to find in C program the length of a table with lua_objlen that 
> returned zero, though there are entries in the table (I made them 
> myself).
> Testing in the lua interpreter gives the following results I cannot 
> explain:
>
> Lua 5.1.3  Copyright (C) 1994-2008 Lua.org, PUC-Rio
> > local io = require "io" print(io, #io)
> table: 0x102080    0
> > local ta= {"a","b","c"} print(ta, #ta)
> table: 0x107af0    3
This is correct according to the reference manual:

> The length of a table t is defined to be any integer index n such that 
> t[n] is not nil and t[n+1] is nil; moreover, if t[1] is nil, n may be 
> zero. For a regular array, with non-nil values from 1 to a given n, 
> its length is exactly that n, the index of its last value. If the 
> array has "holes" (that is, nil values between other non-nil values), 
> then #t may be any of the indices that directly precedes a nil value 
> (that is, it may consider any such nil value as the end of the array).

The io table has no entries with integer indices.  There are a number of 
ways that you can get the total number of entries in a table.  Following 
is one, I'm sure others will post better techniques:

-- tab is the name of the table whose size you want
function tabLen(tab)
   local count = 0
   table.foreach(tab, function(k,v) count = count+1 end)
   return count
end



-- Matt