几道C++笔试题

#include <iostream>
using namespace std;

class A
{
public:
    A()
    {
        print();
    }
    void fun()
    {
        print();
    }
    virtual void print()
    {
        cout<<"A::print()"<<endl;
    }
    int m;
};

class B: public A
{
public:
    virtual void print()
    {
        cout<<"B::print()"<<endl;
    }
}

int main()
{
    B b; // A::print()
    A * a = &b;
    a->print(); // B::print()
    b.fun();    // B::print()
    return 0;
}

#include <iostream>
#include <string>
using namespace std;

class A
{
public:
    A()
    {
        memset(this,0,sizeof(*this));
    }
    virtual void print()
    {
        cout<<"A::print()"<<endl;
    }
private:
    //string s;
    int m;
};

class B: public A
{
public:
    virtual void print()
    {
        cout<<"B::print()"<<endl;
    }
};

int main()
{
    A a;
    B b;
    //静态调用没有问题
    a.print(); // A::print()
    b.print(); // B::print()

    //动态调用，实际类型为B，也没有问题，因为B的虚函数表没有被破坏
    A & aa = b;
    aa.print(); // B::print()
    A * pa = &b;
    pa->print(); // B::print()

    //B自己通过指针调用也没有问题，虚表没有被破坏
    B * pb = &b;
    pb->print(); // B::print()

    //A自己通过指针调用崩溃，虚表被破坏
    //A * pa = &a;
    //pa->print(); // crash!

    return 0;
}

#include <iostream>
#include <string>
using namespace std;

typedef struct Test
{
    string name;
    int     a;
}Test;

int main()
{
    Test tTest;
    memset(&tTest, 0, sizeof(Test));
    return 0;
}