RE: Calling a function defined in lua from C/C++

["Jerome Vuarand" <jerome.vuarand@...>]

Answer to Issue One :

 

The problem with your example is that in your c code you are calling lua_tocfunction (look at the "c" between "to" and "function"), which explicitly return a pointer to a C function as Lua likes them (that is taking a lua_State* and returning an int). funk is a pure Lua function, so lua_tocfunction returns NULL.

 

In manual there : http://www.lua.org/manual/5.1/manual.html#lua_tocfunction

---

De : lua-bounces@bazar2.conectiva.com.br [mailto:lua-bounces@bazar2.conectiva.com.br] De la part de Turgut Hakki ÖZDEMIR
Envoyé : 10 mai 2006 09:19
À : lua@bazar2.conectiva.com.br
Objet : Calling a function defined in lua from C/C++

Greetings,

I saw lua used on a cpu-hunger project, loved it 
(speed issues (another nearly same project, using python is running several 
times slower...(needless to say, i'm involved))) and start to tinker with it to 
embed it my own projects but i've ended up with several problems. 

Issue 
one :) :  When i try to call lua functions from C++ code it is complaining 
about "attempt to call a nil value" or something similar. I've checked reference 
manual and wiki several times but it did not changed anything. Finally i've 
noticed all functions defined in lua scripts has nil values but C++, functions 
registered to lua are callable. Also other global variables (non function ones) 
appearing as they have to be. 

Following code represents the problem. 

Code is compiled using msvc++ 2005 express edition and lua 5.1 (compiled 
as c++ and linked as a static library) (i've tried whole thing also in c but the 
result is same) 

stringf class is provided for compilation reasons and 
does not related with our subject :)

--- test.lua 
---------------------------------
function funk()

end

msg(funk) 
-- will be nil
msg(msg) -- displays functions address 
-------------------------------------------------

and the 
code

--- blabla.cpp  ----------------------------
#include 
<stdio.h>
#include <string>

#include 
<windows.h>

#include <lua.h>
#include 
<lualib.h>
#include <lauxlib.h>

// --- printf like string 
formatter --------------------------
class stringf
{
  protected 
:
    std::string str;
  public : 
    stringf(const char *fmt, ...) 
{
      va_list 
va;
      char 
*tmp;

      va_start(va, 
fmt);
      tmp = new char [vsnprintf(0, 0, fmt, va) 
+ 1];
      vsnprintf(tmp, vsnprintf(0, 0, fmt, va) 
+ 1, fmt, va); 
      str = 
tmp;
      delete [] 
tmp;
      va_end(va);
    
}

    operator const char * () 
{
      return str.c_str();
    
}
    operator std::string () 
{
      return str;
    
}
};

// --- Message box emulation ----------------------
int 
msg(lua_State *L)
{
int n = lua_gettop(L);
std::string 
msg;

  for (uint i = 1; i <= n; i++) {
    
switch(lua_type(L, i)) {
      case LUA_TFUNCTION : 
          msg += (const char *) 
stringf("(function) : 0x%x", lua_tocfunction(L, 
i));
        break;
    
}

  }

  MessageBox(0, msg.c_str(), "Message", 
MB_OK);

return 0;
}

// --- Start crying here 
--------------------------
int WinMain(HINSTANCE hInstance, HINSTANCE 
hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{ 
    
lua_State *L = lua_open();
    
luaL_openlibs(L);
    
    luaL_loadfile(L, 
"test.lua");
   
    lua_register(L, "msg", 
msg);
    
    lua_call(L, 0, 0); // when i 
use lua_pcall instead of lua_call here, surrounded with error handling 
functionality it complains about nil values 
   
    
lua_close(L);
}
-----------------------------------


Issue two : 
How can i convert exceptions (derived from std::exception) to lua? Well, i can 
do it by altering luaconf.h (i think) but how are you doing this? 

  
C++ code starts a script
  script calls a C++ function
  C++ 
function gets frightened and raises an exception
  How the script can 
handle thrown exception?

Issue four : What about C++ interoperatability? 
Any wrappers? (Actually i saw one but ended up with 404 error), How can i 
represent my classes/objects in lua in a little bit reasonable way (saw wiki). 
Where is the gooooooood sample "let's involve c++" code? :) 

Issue three: 
Unicode?