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I once did a kind of linking of C variables to Lua, but I can't find the
code right now...

The C implementation was something along

float f;

static void l_getfloatvar()
{   void *ptr = lua_getusertag(lua_lua2C(2)); /* Err check omitted */


static void l_setfloatvar()
{   void *ptr = lua_getusertag(lua_lua2C(2)); /* Err check omitted */
    double x = lua_getnumber(lua_lua2C(3));

    *(float*)ptr = x;

void init_lua_cvars()
{ int tag_floatvar = lua_newtag();
  lua_pushcfunction(l_getfloatvar); lua_settagmethod(tag_floatvar,
  lua_pushcfunction(l_setfloatvar); lua_settagmethod(tag_floatvar,
  /*** similarly for other C types ***/

  lua_pushusertag(tag_float, &f); lua_setglobal("C_variable_f");

The value of the C variable f can then be queried and assigned using the
lua variable C_variable_f.
This obviously shouldn't be used for dynamic or automatic variables.

You might even call a function inside the tag methods to notify your
program of a Lua program getting or setting your variable in a way
similar to tcl's variable tracing facility; Unfortunately, you won't be
able to intercept a C function accessing the variable that easily.

Adolf Mathias              EMail: dolfi at zkm dot de  Web:
|||| / |< ||| ZKM Institute for Visual Media - Institut für Bildmedien
P.B. 6919 D-76049 Karlsruhe, Germany; fon +49 721-8100-1544, fax -1509