extern "C" needed about llua HOT 2 OPEN

Yes, good point. llua.h must have extern "C" - I want to try it out in C++ mode for the Microsoft compiler anyway.

from llua.

I found a way lua takes for this kind of issue:

Because you can compile Lua both as C and as C++ code, lua.h does not include this typical adjustment code that is present in several other C libraries:

#ifdef __cplusplus
extern "C" {
#endif
   ...
#ifdef __cplusplus
}
#endif

Therefore, if you have compiled Lua as C code (the most common case) and are using it in C++, you must include lua.h as follows:
extern "C" {
#include <lua.h>
}
A common trick is to create a header file lua.hpp with the above code and to include this new file in your C++ programs.

But from 5.1 lua includes lua.hpp as shown below:

// lua.hpp
// Lua header files for C++
// <<extern "C">> not supplied automatically because Lua also compiles as C++

extern "C" {
#include "lua.h"
#include "lualib.h"
#include "lauxlib.h"
}

from llua.