Re: Lua 5. 2 Length Operator and tables (bug? ) In reply to this post by Matthew Wild Matthew Wild gmail. com writes: On 16 April 2012 09: 31, gmx. com wrote: My point in this is that if# t returns a particular value n, it becomes surprising if each key of 1. n Lua table size operator manual not index a non nil value in the table. Apr 16, 2015 pairs(table) Lua provides a pairs() function to create the explist information for us to iterate over a table.
The pairs() function will allow iteration over keyvalue pairs. Note that the order that items are returned is Useful Operations on Tables.
Some notes on terminology: Lua tables are usually listlike (like an array) or maplike (like an associative array or dict); they can of course have a listlike and a maplike part. Some of the table operations only make sense for listlike tables, and some only for maplike tables. The implementation described in this manual is available at Lua's official web site, www. lua. org. Like any other reference manual, this document is dry in places.
Operator precedence in Lua follows the table below, from lower to higher priority: sizet luastringtonumber (luaState L, const char s); A table is an official Lua data type. An array is a computer science concept that can be implemented with a Lua table. Tables can also implement: Data dictionaryhash Data structures (like C struct) Database tables (in memory) OOP classes Stacks Queues None of the preceding is actually a part of Lua, but all can be implemented This should be simple, and it probably is, but in my C code, I want to know the size of a table before I start iterating trough it.
I need to preallocate some memory to store values in that come from Why is Lua designed such that fetching the size of a table is O(n) in the size of the table? Update Cancel. time in the length of the table, and the primitive length operator is specified in such a way that this complexity seems optimal to me. While I can think of an equally reasonable way of defining the operator that would permit a Lua 5.
3 Reference Manual by Roberto Ierusalimschy, Luiz Henrique de Figueiredo, Waldemar Celes, so that a call table. remove(l) removes the last element of list l If comp is not given, then the standard Lua operator is used instead. Note that the comp function must define a strict partial order over the elements in the list; that is Lua 5.
3 Reference Manual The reference manual is the official definition of the Lua language. For a complete introduction to Lua programming, see the book Programming in Lua.
Note: For index based tables you can get the size with the# operator: This is the standard Lua way of getting the size of index tables i.
e. ipairs() type of tables with numerical indices. To get the size of tables that use user defined keys instead of automatic indices (pairs() type) you need to use the function table. size() referenced The table library is explained in section 5. 5 of the Reference Manual.
There are more details about tables in the TablesTutorial. The manual is concise about the purpose of Arithmetic Operators. Lua supports the usual arithmetic operators: the binary (addition), (subtraction), (multiplication), (division), (modulo), and (exponentiation); and unary (negation).
If the operands are numbers, or strings that can be converted to numbers (see ), then all operations have the usual meaning. Exponentiation The Lua 5. 1 reference manual has this to say about it: The length of a table t is defined to be any integer index such that t[n is not nil and t[n1 is nil.
In other words, be careful with this operator if you are using tables with holes in them.