C++ traverses the lua table example

C /c++ gets the table data from Lua on the stack

map<string,string> traverse_table(lua_State *L, int index)
{
 map<string,string> data;
    lua_pushnil(L); 
    //Current stack: -1 => Nil; The index => The table
 index = index - 1;
    while (lua_next(L, index))
    {
        //Current stack: -1 => The value; - 2 => The key; The index => The table
        //Copy a copy of the key to the top of the stack and then do lua_tostring on it without changing the original key value
        lua_pushvalue(L, -2);
        //Current stack: -1 => The key; - 2 => The value; - 3 => The key; The index => The table

        const char* key = lua_tostring(L, -1);
        const char* value = lua_tostring(L, -2);

  data[key]=value;
        //Pop up the value and the copied key, leaving the original key as the next lua_next argument
        lua_pop(L, 2);
        //Current stack: -1 => The key; The index => The table
    }
    //Current stack: index => Table (by the time lua_next returns 0, it has already popped the key left over from the last time)
    //So the stack is back to where it was when we entered this function
 return data;
}