Insert randomly generated strings as nested table - string

Question

These days I am working on a small example/project of myself. What I am doing is creating n set of random strings of variable lengths. Here is what I want to obtain:
Two names of length from 3 to 25 characters.
A message ranging from 40 to 300 characters.
In my C example, I create a struct and kept inserting into this table as list. In my LUA example, I want a nested table like this:
tTableName = {
[1] = {
"To" = "Name 1",
"From" = "Name 2",
"Message" = "The first message generated"
}
[2] = {
"To" = "Name 3",
"From" = "Name 4",
"Message" = "The second message generated"
}
}
So, basically my structure goes like this:
struct PM {
char *sTo, *sFrom, *sMessage;
} PMs;
I want a similar structure/table in LUA so that I can use a table.insert method. I currently am doing it like this:
tTempTable = {
"To" = "Name 1",
"From" = "Name 2",
"Message" = "The first message generated"
}
table.insert( tTableName, tTempTable )
but I am thinking it as a wastage of a lot of processing time. Currently I am only generating a sample of 30 such PMs; but later I shall be generating *1000*s of them. Please advice.

Answer 1

i think you're falling into the trap of pre-maturely optimizing your code before you even know where a bottleneck is... but the following document contains a bunch of optimization info about lua in general, including tables. The guy who wrote it is one of the head architects for Lua.
http://www.lua.org/gems/sample.pdf

Answer 2

First of all, this isn't really a question. I'll guess you're asking if there's a more efficient way to do this? In general you want to write for clarity and don't sweat small performance gains at all unless you run into issues. But here are some notes about your code, including a few notes about efficiency:
The table constructor posted isn't valid. Either of the following fixes would work:
tTempTable = {
["To"] = "Name 1",
["From"] = "Name 2",
["Message"] = "The first message generated"
}
tTempTable = {
To = "Name 1",
From = "Name 2",
Message = "The first message generated"
}
You don't need to specify numerical indexes when constructing an array. You can replace this:
tTableName = {
[1] = { To = "Name 1", From = "Name 2", Message = "The first message generated" },
[2] = { To = "Name 3", From = "Name 4", Message = "The second message generated" },
}
With this, which means the exact same thing but is more succinct:
tTableName = {
{ To = "Name 1", From = "Name 2", Message = "The first message generated" },
{ To = "Name 3", From = "Name 4", Message = "The second message generated" },
}
This also happens to be more efficient; Lua can preallocate the array size it needs, whereas it's not smart enough to do that with the previous constructor.
As for a better way to write this in general, it's hard to say without knowing more about your application. If you're just trying to test some PM code, why not just generate the strings you need on the fly at the point of use? Why preallocate them into a table at all?
If you must preallocate, you don't have to store them as structured data. You could just have three arrays: ToNames, FromNames, Messages, then select from them at random at the point of use:
local to = ToNames [ math.random(1,#ToNames ) ]
local from = FromNames[ math.random(1,#FromNames) ]
local message = Messages [ math.random(1,#Messages ) ]
TestPM(to, from, message)