virtual destructor in shared_ptr

[ltqusst]

Consider following code

#include <iostream>
#include <memory>

using namespace std;

struct base{
    ~base() {
        std::cout << "base(" << this << ") is destructed!\n";
    }
};

struct derived: public base{

    ~derived(){
        std::cout << "derived(" << this << ") is destructed!\n";
    }
    std::shared_ptr<std::string> a;
};


void test1(){
    std::cout << "====== test1()\n";
    base * p = new derived();
    delete p;
}

void test2(){
    std::cout << "====== test2()\n";
    std::shared_ptr<base> p = std::make_shared<derived>();
}

int main()
{
    test1();
    test2();
    return 0;
}

and console output:

====== test1()
base(0x55894e2962c0) is destructed!
====== test2()
derived(0x55894e2962f0) is destructed!
base(0x55894e2962f0) is destructed!

test1() shows that virtual destructor is needed when delete normal pointer, but test2 shows that is not needed for shared_ptr cases, why?
it may be that the shared_ptr up-cast keep deleter unchanged, thus no need for virtual destructor.

[ltqusst]

answers:

The shared_ptr remembers the pointer type used during construction

https://www.geeksforgeeks.org/virtual-destruction-using-shared_ptr/