如何在内存中获取对象大小？

#include<iostream>

class MyClass {
public:
    int x;
    double y;
};

int main() {
    MyClass obj;
    std::cout << "Size of MyClass: "<< sizeof(obj)<< std::endl;
    return 0;
}

import java.lang.instrument.Instrumentation;

public class ObjectSize {
    private static Instrumentation instrumentation;

    public static void premain(String agentArgs, Instrumentation inst) {
        instrumentation = inst;
    }

    public static long getObjectSize(Object obj) {
        return instrumentation.getObjectSize(obj);
    }
}