Re: String parameters when calling C from Lua

[askok@...]

Lua authors!!!:
 :)

Would it be possible to have a "lua_pushstring_fixed()" 
API function, to cover this issue.  That is, any pushings 
of a string that _relies_ on the pointer not to change 
after exit back to Lua world, would use such function to 
make the point. Normal string pushing would be seen as 
temporary.

With current (5.1) version, the call could be simply a 
macro doing the normal push.

-asko


On Fri, 19 May 2006 13:21:29 +0200
 Mike Pall <mikelu-0605@mike.de> wrote:
> Hi,
>
> Daniel Collins wrote:
> > The strings are immutable but need to persist in C 
> > longer than the
> > duration of the API function called from Lua. So the 
> > string parameter
> > passed in my method one would need to be copied into 
> > another buffer.
>
> Ok, a returned string pointer is guaranteed to be valid 
> as long
> as the corresponding Lua string exists in the Lua stack 
> (see the
> description of lua_tolstring() in the Lua 5.1 manual).
>
> But the current GC algorithm (as of Lua 5.0/5.1) does 
> not move
> objects. So right now you can also rely on the fact that 
> the
> string pointer is valid as long as there is _any_ 
> reference to it
> (i.e. from the table you use to store them). 
>
> Yes, the latter means relying on implementation 
> internals. But
> nobody forces you to upgrade to a newer Lua version. The 
> C API
> usually changes over major versions, anyway.
>
> Bye,
>     Mike