could I create an empty class with a specific size?

Question

I made an empty class having specific offset and want to derived class using that area..

like below code.. I use alignas()

#include <iostream>
#include <string>
#include <string.h>

using namespace std;

#pragma pack (push, 1)
class alignas(32) base
{
public:
    base() { init(); }
    void init() { memset(this, 0, 32); }
}; // sizeof(base) = 32

class derived01 : public base
{
    int a;
    int b;
}; // sizeof(derived01) = 32

class derived02 : public base
{
    char a[20];
}; // sizeof(derived02) = 32

class item
{
    int a;
    base b;
    int c;

public: 
    template <typename T>
    inline T GetDerived()
    {
        return reinterpret_cast<T>(&b);
    }
};
#pragma pack (pop)

int main()
{
    cout << "ItemUnit :" << sizeof(base) << endl;
    cout << "derived01 :" << sizeof(derived01) << endl;
    cout << "derived02 :" << sizeof(derived02) << endl;

    cout << "item :" << sizeof(item) << endl;

    // I want to get Derived Class like this..
    //item* i = new item();
    //derived02 d = i.GetDerived<derived02>();

    return 0;
}

and, it seemed to work as expected.. In LINUX.. (g++ 7.4)

# ./a
ItemUnit :32
derived01 :32
derived02 :32
item :40

but in MSVS2019, it returned..

ItemUnit :32
derived01 :32
derived02 :32
item :96

I also thought about other ways, but they have some....

1. UNION but, it cant using inheritance.. and I think it inconvenient to use.

2. make base class having char[32].. and derived having only functions to get,set using offset..

Is there any other good way? please advice..