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- Subject: Re: Eval a Lua expression
- From: Eugen-Andrei Gavriloaie <shiretu@...>
- Date: Thu, 3 Apr 2008 01:58:23 +0300
On Apr 3, 2008, at 1:09 AM, Javier Guerra wrote:
On Wed, Apr 2, 2008 at 4:50 PM, Eugen-Andrei Gavriloaie
On Apr 3, 2008, at 12:27 AM, Javier Guerra wrote:
no, each call to lua_evaluate_expression() would compile and
Hmmm, that is even worse unfortunately because I don't want to
the script over and over again. Some Lua variables may contain
new script in the same context. it won't 'accumulate' a long script.
informations and on the first call
it's not _re_compiling.
first you compile and run your config, that sets one or more 'global'
vars with your data. then you compile and run several *very* short
scripts, each one returns one or a few datums to the stack, where your
C code can easily fetch it/them.
Well, I need to do more reading on this matter. It's obvious that I
don't fully understand the concept of loading,compiling and executing
Here is what I know so far:
1. Instantiate a Lua VM
_pLuaState = lua_newstate(_lua_alloc, NULL);
2. Adding some more standard functionality to the newly created VM
3. Adding custom made functionality represented by c++ functions
At this stage we have a fully working Lua VM with some API provided by
the standard libraries and custom made c++ functions. We will continue
by loading a script into our VM
4. Load a Lua script from disk. This will result in adding 0 or more
APIs (functions written in Lua) and 0 or more already initialized
variables (like my config file who is a bunch of variables).
I think (not 100% sure) that this is only transforming Lua script into
bytecode and loading it into VM
Next step (who seems that I don't fully understand) is start the VM
(give it a kick)
5. lua_pcall(pLuaState, 0, 0, 0)
At this stage, the entire VM is performing it's first step from the
rest of it's life cycle. This is represented by initializing the
global variables from the script (like my config file) and doing some
functions calls (I don't have any in a config file)
6. Now, the cloudy part for me is what is happening when I do a
luaL_loadstring(...). From the docs I understood that the string is
compiled and transformed into byte code and than added to the VM. But
this "adding" process is playing tricks with my mind. What is really
happening there? Is permanently/temporarily added? Is only executed
and after that discarded?
In my point of view (hopefully correct :) ) loading a script means
compiling it into a byte code form and after that make it available to
the VM. What would happen if we do a second luaL_loadfile(...) on the
same lua_State? replacing the previous one or appending? Same question
with the luaL_loadstring(...)
Thank you very much!