Re: Guidance on how to write this Lua C Binding ?

[Peter Odding <peter@...>]

Hi Jeff,

> I want to write a C function that takes a UTF8 Lua string and in C break
> it down into codepoints, each codepoint I want to insert into a Lua
> table using the API and return that table to Lua. I am OK with
> the UTF8 parsing (I have already written that) what I am unsure about is
> how to return the table to Lua when it has potentially  1000 or so
> codepoints in the table ?
>  
> I have previously written a binding that populates a small table and
> returns it to Lua, this was maybe 5 elements max, so I didnt even need
> to worry about the stack size.
>  
> My first question is, is this same technique still valid and sound if
> you have to potentially push a few thousand elements onto the stack to
> return a big table ?

If you extract a code point from the string and immediately add it to
the table, the code point won't be on the stack right? Tables take up
one slot of the stack no matter how many values they contain. So as long
as you add each code point to the table immediately you shouldn't need
to worry about the size of the Lua stack.

> if the answer to that is yes, can you point me at an example of how to
> grow the stack to suit as needed, and what do I need to do to shrink the
> stack when I have finished with this function ?

As I tried to explain above you don't need to grow the stack to do what
you want to do. However should you need to grow the stack you can call
lua_checkstack() to ensure enough space on the stack:

http://www.lua.org/manual/5.1/manual.html#lua_checkstack

> If however returning a big table by pushing it all on the stack, is not
> sound practice, how should this be achieved instead ? Any links to study ?

The table can be as big as you want it to, there's nothing unsound about
this! :-)

 - Peter