c++ virtual inheritance

virtualInheritanceDemo.cpp

#include<iostream>
using namespace std;

//大小为4
class A
{
public:
    int a;
};

//在64位环境下，变量a 4个字节，b 8个字节，虚基类表指针8个字节，为了对齐，大小总共24
class B :virtual public A
{
public:
    double b;
};

//与B一样
class C :virtual public A
{
public:
    double c;
};

//在64位环境下,大小为48,变量a 4,b 8,c 8,d 8加对齐共 32，B的虚基类指针 8，C的虚基类指针 8
class D :public B, public C
{
public:
    double d;
};

int main()
{
    cout << "int size: " << sizeof(int) << endl;
    cout << "double size: " << sizeof(double) << endl;
    cout << "pointer size: " << sizeof(void*) << endl;
    cout << "---------------------------" << endl;
    cout << "objec A: " << sizeof(A) << endl;
    cout << "objec B: " << sizeof(B) << endl;
    cout << "objec C: " << sizeof(C) << endl;
    cout << "objec D: " << sizeof(D) << endl;

    return 0;
}

/* int size: 4
double size: 8
pointer size: 8
---------------------------
objec A: 4
objec B: 24
objec C: 24
objec D: 48 */