How do I access and set a variable from a class made in C ++ to Lua?

// C++
#ifndef SCRIPTSTORAGE_H
#define SCRIPTSTORAGE_H

#include "HTest.h"

#include <luajit/lua.hpp>
#include <iostream>

struct HObject {
    unsigned int id;
    std::string name;
    float x, y, z;
    float sx, sy, sz;
    float u, v;

    HObject()
    {
        id = 1;
    }
};

static bool checkFunctionArgs(lua_State* ls, const char* fname, unsigned int nargs)
{
    int fnargs = lua_gettop(ls) - 1;

    if(fnargs < (int)nargs)
    {
        std::cout << "LuaScriptError: " << fname << "() need at least %d parameter(" << nargs << ")n" << std::endl;;
        return true;
    }

    if(fnargs > (int)nargs)
    {
        std::cout << "LuaScriptError: " << fname << "() takes " << nargs << " positional arguments but " << fnargs << " were given" << std::endl;
        return true;
    }

    return false;
}

HObject* HObject_check(lua_State* ls, int index)
{
    void* ud = 0;

    luaL_checktype(ls, index, LUA_TTABLE);
    lua_getfield(ls, index, "__self");

    ud = luaL_checkudata(ls, index, "HObject:new");

    luaL_argcheck(ls, ud != 0, 0, "'HObject:new' expected");

    return *((HObject**)ud);
}

static int HObject_newHObject(lua_State* ls)
{
    if(checkFunctionArgs(ls, "HObjec:new", 0)){
        return 0;
    }

    luaL_checktype(ls, 1, LUA_TTABLE);
    lua_newtable(ls);

    lua_pushvalue(ls, 1);
    lua_setmetatable(ls, -2);

    lua_pushvalue(ls, 1);
    lua_setfield(ls, 1, "__index");

    HObject** obj = (HObject**)lua_newuserdata(ls, sizeof(HObject*));
    *obj = new HObject();

    luaL_getmetatable(ls, "HObject:new");
    lua_setmetatable(ls, -2);

    lua_setfield(ls, -2, "__self");

    return 1;
}

static int HObject_destructor(lua_State* ls)
{
    HObject* obj = HObject_check(ls, 1);
    delete obj;

    return 1;
}

void HTest_register(lua_State* ls)
{
    static const luaL_Reg hobjec_funcs[] = {
        {"new", HObject_newHObject},
        {"__gc", HObject_destructor},
        {NULL, NULL}
    };

    luaL_newmetatable(ls, "HObject:new");
    luaL_register(ls, 0, hobjec_funcs);
    lua_pushvalue(ls, -1);
    lua_setfield(ls, -2, "__index");

    luaL_register(ls, "HObject", hobjec_funcs);
}

#endif // SCRIPTSTORAGE_H


-- Lua
local obj = HObject:new() -- OK

obj.variavel = 10 -- Exemplo de escrever na variável
print(obj.variavel) -- Exemplo de acessar variável

I want to access and write in the variable, but I do not know how to link the same in Lua. I have already managed to link the class HOBject along with its functions,
    

There is no standard way of establishing variable access in LUA. You have two options to work around this:

Getter and Setters

The first one is easier, but it may seem kind of ugly. You can create getters and setters. So you would have to create a get and set pair for each variable you want to have accessible, for example:

static int getVariavel(lua_State* ls)
{
    //Obter seu objeto aqui
    lua_pushinteger(ls, obj->variavel);
    return 1;
}
static int setVariavel(lua_State* ls)
{
    //Obter seu objeto aqui
    obj->variavel = lua_tointeger(ls, -1);
    lua_pop(1);
    return 0;
}

You have to create a pair of these for each variable, but this can be simplified with the help of macros and / or templates. With this template you can access and change the variables as follows:

local obj = HObject:new() -- OK
obj:setVariavel(10) -- Exemplo de escrever na variável
print(obj:getVariavel()) -- Exemplo de acessar variável

Filtering by __index __newindex

The other way would be to place handlers for the __index and __newindex events in the metatable of the objects. So you could filter the variable names and return their values:

static int index(lua_State *ls)
{
    ///Obter objeto aqui.
    string s = lua_tostring(ls, 2);
    if(s == "variavel")
        lua_pushinteger(ls, obj->variavel);
    else if(s == "variavel2")
        lua_pushinteger(ls, obj->variavel2);
    // Outras variáveis aqui.
    else
    {
        //Chamar a table com as funções.
    }
    return 1;
}
static int newIndex(lua_State *ls)
{
    //Obter objeto aqui
    string s = lua_tostring(ls, 2);
    if(s == "variavel")
        obj->variavel = lua_tointeger(ls, -1);
    else if(s == "variavel2")
        obj->variavel2 = lua_tointeger(ls, -1);
    //..outras variáveis aqui.
    else
        //Mostrar msg de erro dizendo que tal variável não existe.
}

This model needs only these two functions, but comparing strings one by one can be slow if you have a very large number of attributes and your class. On the other hand, access on Lua looks more beautiful, in my opinion:

-- Lua
local obj = HObject:new() -- OK

obj.variavel = 10 -- Exemplo de escrever na variável
print(obj.variavel) -- Exemplo de acessar variável