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uglybdavis

LUA load file into table

4 posts in this topic

This question relates to the lua c api. Lets say i have a file like this one: 

helloString = "Hello World"

function fwrite (fmt, ...)
     return io.write(string.format(fmt, unpack(arg)))
end

And i want to load it into a global table named loadedScript such that at a later point i can call fwrite like loadedScript.fwrite

Ideally i would like to load the file and assign it's contents to the global table trough the C API.

 

I'm new to lua, and have no idea what to even look for to solve this.

Anyone have any ideas?

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There's no direct way of loading script contents into a global table.
You have two options, one of which is easy, and the other requires too much knowledge about the script on the C/C++ side.
 
One option is to change your script so that the function and all other properties you want are already defined as being in the table, like so:

loadedScript = {}

loadedScript.helloString = "Hello World"

function loadedScript.fwrite(fmt, ...)
    return io.write(string.format(fmt, unpack(arg)))
end

The other way requires that on the C/C++ side you know the contents of the script, and is a bit longer. You manually create a table, and assign each of the values in the script to be a part of that table, something like this:

//functions used:
//http://pgl.yoyo.org/luai/i/luaL_dofile
//http://pgl.yoyo.org/luai/i/lua_createtable
//http://pgl.yoyo.org/luai/i/lua_pushstring
//http://pgl.yoyo.org/luai/i/lua_gettable
//http://pgl.yoyo.org/luai/i/lua_settable
//http://pgl.yoyo.org/luai/i/lua_pushnil

//first run the script file so you get the values inside into the global table
luaL_dofile(L, "your_script_file.lua");

//now that everything in the script is in the global table, create your loadedScript table
lua_createtable(L, 20, 20);

//then get the existing fields from the global table and push them into the newly created one
//first, push the name of the field twice (we need it for later)
lua_pushstring(L, "helloString");
lua_pushstring(L, "helloString");
//then get the value
lua_gettable(L, LUA_GLOBALSINDEX);
//then, set the value to be part of the new table
lua_settable(L, -3);

//now repeat for the function
lua_pushstring(L, "fwrite");
lua_pushstring(L, "fwrite");
lua_gettable(L, LUA_GLOBALSINDEX);
lua_settable(L, -3);

//optionally, you can remove the global versions by setting their value to nil
lua_pushstring(L, "helloString");
lua_pushnil(L);
lua_settable(L, LUA_GLOBALSINDEX);
lua_pushstring(L, "fwrite");
lua_pushnil(L);
lua_settable(L, LUA_GLOBALSINDEX);

 
As you can see, this way you require complete knowledge of the script contents in the C++ world, since there is no way to know what variables the script contains (at least not a practical way which doesn't involve writing your own parser which generates an intermediate script file that looks like the first option i gave).

Edited by Strewya
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If you are using Lua 5.1 you can use setfenv to alter the global table the function will be run in.

loadedScript = {}
f = loadfile("myscript.lua")   --use loadfile to load the script but don't execute it yet
setfenv(f,loadedScript)
f()

You might also want to redirect lookups to the original global table so you can use io.write in loadedScript

 

There should be something similar in Lua 5.2(setfenv() was removed) but I'm not familiar with it.

mt = {
__index = _G   -- if we can't find something in loadedScript, try global table instead
}
setmetatable(loadedScript,mt)
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