Bus error using lua_touserdata

[Costas Calamvokis <cc28@...>]

I have a problem: when I call lua_touserdata() on a file pointer
in the io table I get a bus error.

I'm doing this because I need to go through all variables and do 
something for any I find that are of a particular userdata type (using C++).

I have this working pretty much, I start at _G, recurse through 
everything and when I find userdata I do this:

     if ( lua_type(L,-1) == LUA_TUSERDATA ) {
        int *ud =(int *) luaL_checkudata_noerror(L, -1, utype);
        if (ud != NULL) {

Where luaL_checkudata_noerror is just a copy of luaL_checkudata from
the auxlib with the bit that generates a error if the type is wrong
commented out, the start looks like:

LUALIB_API void *luaL_checkudata_noerror (lua_State *L, int ud, const 
char *tname) {
  void *p = lua_touserdata(L, ud);

^that's the line that gives the bus error, when it is called with
one of the file pointers.

I think it may have something to do with the environment of the 
userdata? But I'm not sure how to fix it.

Alternatively, if there was a way to avoid recursing into the library 
stuff without having a list of things to skip (which is my current 
workaround), that would be nice too.

thanks,
Costas