Calling lua functions from .lua's using handles?

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I'm working on a small project trying to integrate lua with c++. My problem however is as follows:

I have multiple lua scripts, lets call them s1.lua s2.lua and s3.lua. Each of these has the following functions: setVars() and executeResults().

Now I am able to to call a lua file through LuaL_dofile and immediately after use setVars() and/or executeResults(). The problem here however is that after I load s2.lua I can no longer call the functions of s1.lua. This would mean I have to redo the LuaL_dofile on s1.lua to regain access to the function and by doing so I lose access to the functions in s2.lua.

Is there a way to simply load all lua files in a row, and afterwards start calling their functions at will? Something like s1->executeResults() s5->executeResults() s3->setVars() etc.

I currently already have a system in place using boost::filesystem to detect all lua files in a folder, I then save these files names in a vector and then simply iterate over the vector to load each lua file in a row.

Foregoing the filling of the vector with lua file names my plugin load function looks like this at the moment:

void Lua_plugin::load_Plugins(){ std::vector<std::string>::const_iterator it; for (it=Lua_PluginList.begin(); it!=Lua_PluginList.end(); it++){ std::cout<<"File loading: " << *it << std::endl; std::string filename = *it; std::string filepath = scriptdir+filename; if (luaL_loadfile(L, filepath.c_str()) || lua_pcall(L, 0, 0, 0)) { std::cout << "ScriptEngine: error loading script. Error returned was: " << lua_tostring(L, -1) << std::endl; } } }

To make it a bit more clear, all I have in the .lua's is something like this:

-- s1.lua setVars() --do stuff end executeResults() --dostuff end

etc, but I would like to be able to call s1.lua's setVars() and s2.lua's setVars() after simply having loaded both in a row.

c++  lua  lua-api share improve this question edited Aug 10 '10 at 15:05 Andreas Bonini 23.5k 20 101 140 asked  Aug 7 '10 at 22:08 Karrok 55 1 11   add a comment

3 Answers

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This is effectively what gwell proposed using the C API:

#include <stdio.h> #include "lua.h" static void executescript(lua_State *L, const char *filename, const char *function) { /* retrieve the environment from the resgistry */ lua_getfield(L, LUA_REGISTRYINDEX, filename); /* get the desired function from the environment */ lua_getfield(L, -1, function); return lua_call(L, 0, 0); } static void loadscript(lua_State *L, const char *filename) { /* load the lua script into memory */ luaL_loadfile(L, filename); /* create a new function environment and store it in the registry */ lua_createtable(L, 0, 1); lua_getglobal(L, "print"); lua_setfield(L, -2, "print"); lua_pushvalue(L, -1); lua_setfield(L, LUA_REGISTRYINDEX, filename); /* set the environment for the loaded script and execute it */ lua_setfenv(L, -2); lua_call(L, 0, 0); /* run the script initialization function */ executescript(L, filename, "init"); } int main(int argc, char *argv[]) { lua_State *L; int env1, env2; L = (lua_State *) luaL_newstate(); luaL_openlibs(L); loadscript(L, "test1.lua"); loadscript(L, "test2.lua"); executescript(L, "test1.lua", "run"); executescript(L, "test2.lua", "run"); executescript(L, "test2.lua", "run"); executescript(L, "test1.lua", "run"); return 0; }

Test scripts:

-- test1.lua function init() output = 'test1' end function run() print(output) end -- test2.lua function init() output = 'test2' end function run() print(output) end

Output:

test1 test2 test2 test1

I omitted all error handling for brevity, but you'll want to check the return value of luaL_loadfile and use lua_pcall instead of lua_call.

share improve this answer answered  Aug 9 '10 at 14:39 Judge Maygarden 18.5k 5 51 84   add a comment up vote 1 down vote

The setfenv() function can be used to create a sandbox or environment for each file loaded.

This example shows that all three files could be loaded with conflicting functions and that the functions can be called in any order. Similar code could be written in C++. This example only exports the print function to each environment, more might be needed in your scenario.

function newEnv() -- creates a simple environment return {["print"]=print} end local e={} -- environment table local c -- chunk variable -- first instance c = loadstring([[function f() print("1") end]]) e[#e+1] = newEnv() setfenv(c, e[#e]) -- set the loaded chunk's environment pcall(c) -- process the chunk (places the function into the enviroment) -- second instance c = loadstring([[function f() print("2") end]]) e[#e+1] = newEnv() setfenv(c, e[#e]) pcall(c) -- third instance c = loadstring([[function f() print("3") end]]) e[#e+1] = newEnv() setfenv(c, e[#e]) pcall(c) pcall(e[3].f) --> 3 pcall(e[2].f) --> 2 pcall(e[1].f) --> 1 pcall(e[1].f) --> 1 pcall(e[2].f) --> 2 pcall(e[3].f) --> 3

share improve this answer answered  Aug 8 '10 at 2:58 gwell 2,110 12 18     First off, thanks! I was looking around in the c++ part of lua and I'm not able to find which function would replace the setfenv() of lua in a c++ environment. This mostly because I would like to retain addon/plugin control in my c++ code (aside from being a bit more versed in c++ compared to lua). And would I be correct in assuming that I could then incorporate the environment creation in my Load_Plugins() function? Having the environment list usable by other parts of the c++ code? Thanks in advance –  Karrok  Aug 8 '10 at 3:42   Correction found pgl.yoyo.org/luai/i/lua_setfenv Darting though the lua-users.org listings it would suggest this function is deprecated though, but I'll try it anyway :) –  Karrok  Aug 8 '10 at 4:04   Deprecation would depend on the version of Lua you are using. setfenv() will be deprecated in 5.2. See corsix.org/content/look-lua-52-work3 –  gwell  Aug 8 '10 at 4:15   Some trying later, and I can't for the life of me figure out how the above lua code would translate into c++ :(. I'm assuming I'm not using the lua_setfenv and lua_getfenv correctly since the application simply crashes. –  Karrok  Aug 8 '10 at 4:55 add a comment up vote 1 down vote

You could create a new state lua_newstate() for each file. This would be easier than my previous answer. However, it may have a performance penalty.

share improve this answer answered  Aug 9 '10 at 2:54 gwell 2,110 12 18     Well if creating the new state only once for each lua file isn't too big a performance penalty then it should not be a problem. The secondary and following access to the states should not occur that often. I think i'll try the newstate thingy because I still can't get the lua_setfenv to work without it crashing the app :( Thanks again :)–  Karrok  Aug 9 '10 at 4:35