why sizeof(tp2) I get 32 instead of 28, int(4) + int(4) + float(4) + complex(16) == 28,but this code get 32

#include <iostream>
#include <tuple>
#include <string>
#include <complex>
using namespace std;
int main() {


    // cout << sizeof(int) << endl;
    // cout << sizeof(string) << endl;
    // tuple<int, int, string> tp;
    // cout << sizeof(tp) << endl;


    tuple<int, int, float, complex<double>> tp2;
    cout << sizeof(tp2) << endl;
    return 0;
}

I guess the reason is the memory aligment, but I do not know is it right?