Compiletimesubclassbyte-offsetwithvirtualinheritance

可以使用C++中的dynamic_cast来获取虚继承的子类的偏移量。

示例代码：

#include <iostream>
#include <cstring>

using namespace std;

class Base {
public:
    virtual ~Base() {}
};

class VirtualBase {
public:
    virtual ~VirtualBase() {}
};

class Derived1 : public Base {
public:
    int d1;
};

class Derived2 : public Base, virtual public VirtualBase {
public:
    int d2;
};

int main() {
    Derived1 d1;
    Derived2 d2;

    Base* b = &d1;
    cout << "Derived1 byte offset: " << 
        reinterpret_cast<char*>(&d1) - reinterpret_cast<char*>(b) << endl;

    b = &d2;
    cout << "Derived2 byte offset: " << 
        reinterpret_cast<char*>(&d2) - reinterpret_cast<char*>(b) << endl;

    VirtualBase* vb = dynamic_cast<VirtualBase*>(&d2);
    cout << "Derived2 with virtual inheritance byte offset: " << 
        reinterpret_cast<char*>(&d2) - reinterpret_cast<char*>(vb) << endl;

    return 0;
}