How to bind C++ public variable for access in lua script

What you want to do can be accomplished with the userdata mechanisms, described in the PIL, starting at http://www.lua.org/pil/28.html. Did you already know about this? You wrote "Okay" next to obj:FuncTest(), as if you got that part to work already.

I will give some nice examples from that page. They describe how one can create a C structure like

typedef struct NumArray {
  int size;
  double values[1];  /* variable part */
} NumArray;

Then by registering methods in a library

static const struct luaL_reg arraylib [] = {
  {"new", newarray},
  {"set", setarray},
  {"get", getarray},
  {"size", getsize},
  {NULL, NULL}
};

int luaopen_array (lua_State *L) {
  luaL_openlib(L, "array", arraylib, 0);
  return 1;
}

one can add data and methods to the userdatum, and access them from Lua. Below is using the array operator [], which requires a little bit more work, but they show how to do it.

a = array.new(1000)
a[10] = 3.4         -- setarray
print(a[10])        -- getarray   --> 3.4

Now I'm not positive, but I suppose that since the userdata is a C structure, it couldn't have functions, but only function pointers. Thus in the C you might have to pass in the appropriate members of 'a' to the function.

I found an example from our project that does what you want.

typedef int (*getSetFunction) (lua_State*);

typedef struct luaMyValReg {
  const char *name;
  getSetFunction getter;
  getSetFunction setter;
} luaMyValReg;

#define luaL_reg luaL_Reg

typedef struct luaMyTable {
luaL_reg    *functions;
luaL_reg    *methods;
luaMyValReg *values;
luaMyValReg *arrays;
luaL_reg    *array_methods;
} luaMyTable;

static const struct luaMyValReg lib_val[] = {
   { "key1", MyClass::l_getKey1, MyClass::l_setKey1},
 ...
    {NULL, NULL, NULL}
 }

These are set into a structure and passed to a function that will set up the userdata.

table.functions = (luaL_reg *) &lib_f;
table.methods = (luaL_reg *) &lib_m;
table.values = (luaMyValReg *) &lib_val;
MyClass::initTable(&table, REGNAME, REGID, ARRAY_REGID);

In that function, there is a bit that creates the metatable, and adds each of the fields in the lib_val array. LGlobalState is the lua_State* pointer.

// Register the functions for the Table
luaL_register(LGlobalState, regname, table->functions);

// Stk: Table
// Create the metatable
luaL_newmetatable(LGlobalState, regid);

// Stk: Table metatable
// Register its methods, leaves it on top of the stack
luaL_register(LGlobalState, NULL, table->methods);

// Stk: Table metatable
// Set the metatable
lua_setmetatable(LGlobalState,-2);

// Stk: Table
// Push metatable
lua_getmetatable(LGlobalState, -1);
// Stk: Table metatable

// Add fields to the metatable
int i = 0;
while (table->values[i].name != NULL)
{
    addMetaField(LGlobalState, table->values[i].name, i);
    i++;
}

// Stk: Table, metatable
lua_pop(LGlobalState, 2);
// Stk: empty

if (lua_gettop(LGlobalState) > 0)
    tngL_error(LGlobalState, "%s inconsistant stack size\n", regname);

Here is the function to add the values.

////////////////////////////////////////////////////////////////////////////////
int LUATask::addMetaField(lua_State *L, const char *pKey, int nIndex)
////////////////////////////////////////////////////////////////////////////////
//  Add a field to the metatable.  It must already be on the top
//  of the stack
{
// Stk: metatable
lua_pushstring(L, pKey);
lua_pushnumber(L, nIndex);
// Stk: metatable, string, number
// Use lua_rawset() instead of lua_settable() to avoid
// the __newindex call
lua_rawset(L, -3);
// Stk: metatable
return 1;
}