Lua table C api

Question

I know of: http://lua-users.org/wiki/SimpleLuaApiExample

It shows me how to build up a table (key, value) pair entry by entry.

Suppose instead, I want to build a gigantic table (say something a 1000 entry table, where both key & value are strings), is there a fast way to do this in lua (rather than 4 func calls per entry:

push
key
value
rawset

what does your test program look like, how does it benchmark, and why is that not fast enough? :-) ! — u0b34a0f6ae
– u0b34a0f6ae, Commented May 9, 2010 at 11:36
(also: only 3 function calls are needed per entry: push key, push value, rawset) — u0b34a0f6ae
– u0b34a0f6ae, Commented May 9, 2010 at 11:53

Norman Ramsey · Accepted Answer · 2010-05-09 15:42:30Z

4

What you have written is the fast way to solve this problem. Lua tables are brilliantly engineered, and fast enough that there is no need for some kind of bogus "hint" to say "I expect this table to grow to contain 1000 elements."

answered May 9, 2010 at 15:42

Norman Ramsey

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lhf · Accepted Answer · 2010-05-09 13:47:58Z

1

For string keys, you can use lua_setfield.

answered May 9, 2010 at 13:47

lhf

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Amber · Accepted Answer · 2010-05-09 10:31:45Z

0

Unfortunately, for associative tables (string keys, non-consecutive-integer keys), no, there is not.

For array-type tables (where the regular 1...N integer indexing is being used), there are some performance-optimized functions, lua_rawgeti and lua_rawseti: http://www.lua.org/pil/27.1.html

answered May 9, 2010 at 10:31

Amber

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Puppy · Accepted Answer · 2010-05-09 15:45:24Z

0

You can use createtable to create a table that already has the required number of slots. However, after that, there is no way to do it faster other than

for(int i = 0; i < 1000; i++) {
    lua_push... // key
    lua_push... // value
    lua_rawset(L, tableindex);
}

answered May 9, 2010 at 15:45

Puppy

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2 Comments

anon Over a year ago

you don't need to duplicate the table on the stack? rawset doens't consume the table?

Puppy Over a year ago

No. Rawset only consumes the key and value. Else, how could you ever set more than one k, v pair into one table?

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