Question

Ok, I’ve searched quite a bit, but seem unable to find an answer or example for how to achieve this.

Basically, I have an app that is designed to be portable (built using VC++ in VS2010, but no MFC or managed components, raw WinAPI). I have Lua 5.2 built into it and allow the user to write scripts inside the application. I have multiple glued functions which are exposed to the Lua scripts which handle various WinAPI calls.

However, what I’d like to be able to do is allow the user to write a script in which looks something like this:

require[[Alien/alien]]

local mb = alien.User32.MessageBoxA
mb:types{ 'long', 'long', 'string', 'string', 'long' }
print(mb(0, "Hello World!", "Test", 64))

I simply cannot seem to find a way to do this. I do not want to require the user to install Lua for Windows and, ideally, there be no core.dll and struct.dll from alien; when I tried to do something with those DLLs in ./alien/, it was crashing in Lua5.1.dll because I had LuaForWindows installed, I uninstalled LFW, and then it just states that Lua5.1.dll is missing. I have Lua 5.2 built into my app, so obviously the core/struct DLLs from the Alien rock are expecting Lua5.1.dll to be in the path.

I made a worthless attempt to try to including the Alien src into the project, but doesn’t seem to work that way either.

Any ideas would be greatly appreciated. I’d prefer it all be contained in my app, but I’ll settle for a solution which involves including the libraries in my project to build and bundle in the distribution if that’s the only alternative.

Thanks!

UPDATE:

Ok, thank you Ben Voigt! I think I’m almost there. I’ve pulled in core.c and struct.c and made sure all the paths are there for libffi. Everything compiles without issue, until I try to call luaopen_alien_core in core.c (the alien.core src file), claiming the identifier is undeclared. I’ve tried to declare the function signature in my separate source file that’s trying to make the call, the compile gets further, but fails complaining of an unresolved external.

Clearly this is likely now a general C++ issue (as I’m only a novice in this area). Here’s the general idea of what I have:

//core.c (from Alien project)

(...)

int luaopen_alien_core(lua_State *L) {
  alien_register_library_meta(L);
  alien_register_callback_meta(L);
  alien_register_function_meta(L);
  alien_register_buffer_meta(L);
  lua_getglobal(L, "alien");
  if(lua_isnil(L, -1)) {
    lua_newtable(L);
    lua_pushvalue(L, -1);
    lua_setglobal(L, "alien");
  }
  lua_newtable(L);
  lua_pushvalue(L, -1);
  lua_setfield(L, -3, "core");
  alien_register_main(L);
  return 1;
}

---

//mysource.c (the file attempting to call luaopen_alien_core(L))

void initLua()
{
    L = luaL_newstate();
    luaL_openlibs(L);
    luaopen_alien_core(L);
    (...)
}

This fails to start compiling, issuing the error:

error C3861: 'luaopen_alien_core': identifier not found

Which makes sense, so I add the following line to myheader.h:

int luaopen_alien_core(lua_State *L);

This compiles, but fails to link with:

error LNK2001: unresolved external symbol "int __cdecl luaopen_alien_core(struct lua_State *)" (?luaopen_alien_core@@YAHPEAUlua_State@@@Z)

I’ve tried several things I can think of, with my limited experience, but nothing will satisfy this error. I even tried to move the contents of core.c into mysource.c, but that creates a whole different mess and seemed to be the wrong way to go as it is.

I’m hoping, and imagining, this is something really stupid, but I’m just not sure how to get it to call luaopen_alien_core, which seems to be the final piece I need.

Thanks again!
}

Answer 1

I imagine that the require directive both loads a dynamic library and adds its contents to the active Lua engine.

By linking alien directly into your code, you obviate the need for the dynamic library. But the content enumeration code won’t have run, and you can’t use require to run it, or else it’ll go looking for a DLL file (along with all the DLL dependencies).

So, you should find out what functions that require directive calls after loading the DLL, and call those when creating a Lua engine. Then it will neither be necessary nor allowed for the script to start with require [[Alien/alien]], but Alien objects will be available.