[GeekBand][C++面向对象高级编程]第四周作业

1. 运行结果

先上结论，测试代码见文末。
在Visual Studio 2015 Community中运行得到的结果如下：

sizeof(int) = 4
sizeof(double) = 8
sizeof(char) = 1
sizeof(Fruit) = 32
sizeof(Apple) = 40
Address of Fa[0] = 3DFAD8
Address of Fa[0].no = 3DFAE0
Address of Fa[0].weight = 3DFAE8
Address of Fa[0].key = 3DFAF0
Address of Fa[1] = 3DFAF8
Address of Ab[0] = 3DFA80
Address of Ab[0].no = 3DFA88
Address of Ab[0].weight = 3DFA90
Address of Ab[0].key = 3DFA98
Address of Ab[0].size = 3DFAA0
Address of Ab[0].type = 3DFAA4
Address of Ab[1] = 3DFAA8
请按任意键继续. . .

2. 对象模型图

class Fruit和class Apple的对象模型图

3. 解析

由于VS本身的原因，vptr和最大成员大小一致(测试了codepad等网络编译器，发现部分编译器vptr都是4B)，故vptr占8位。

!! 内存对齐规则：
第一个成员在offset 0的位置，成员依次向下排列。
每个成员放置时的offset位置应是自身大小的倍数。

按此内存对齐规则排列，得到对象模型图，符合测试结果。

测试代码

文件1：Fruit.h

#ifndef __MYFRUIT__
#define __MYFRUIT__

class Fruit
{
private:
    int no;
    double weight;
    char key;
public:
    void print() {}
    virtual void process() {}
    int size_no() { return sizeof(no); }
    int size_weight() { return sizeof(weight); }
    int size_key() { return sizeof(key); }
    int address_no() { return int(&no); }
    int address_weight() { return int(&weight); }
    int address_key() { return int(&key); }
};

class Apple :public Fruit
{
private:
    int size;
    char type;
public:
    void save() {}
    virtual void process() {}
    int size_size() { return sizeof(size); }
    int size_type() { return sizeof(type); }
    int address_size() { return int(&size); }
    int address_type() { return int(&type); }
};

#endif

文件2：Fruit-test.cpp

#include 
#include "Fruit.h"

int main()
{
    Fruit Fa[2];
    Apple Ab[2];
    std::cout << "sizeof(int) = " << sizeof(int) << std::endl;
    std::cout << "sizeof(double) = " << sizeof(double) << std::endl;
    std::cout << "sizeof(char) = " << sizeof(char) << std::endl;
    std::cout << "sizeof(Fruit) = " << sizeof(Fruit) << std::endl;
    std::cout << "sizeof(Apple) = " << sizeof(Apple) << std::endl;
//  std::cout << "sizeof(long double) = " << sizeof(long double) << std::endl;
    (std::cout << std::hex).setf(std::ios::uppercase);
    std::cout << "Address of Fa[0] = " << int(&Fa[0]) << std::endl;
    std::cout << "Address of Fa[0].no = " << Fa[0].address_no() << std::endl;
    std::cout << "Address of Fa[0].weight = " << Fa[0].address_weight() << std::endl;
    std::cout << "Address of Fa[0].key = " << Fa[0].address_key() << std::endl;
    std::cout << "Address of Fa[1] = " << int(&Fa[1]) << std::endl;
    std::cout << "Address of Ab[0] = " << int(&Ab[0]) << std::endl;
    std::cout << "Address of Ab[0].no = " << Ab[0].address_no() << std::endl;
    std::cout << "Address of Ab[0].weight = " << Ab[0].address_weight() << std::endl;
    std::cout << "Address of Ab[0].key = " << Ab[0].address_key() << std::endl;
    std::cout << "Address of Ab[0].size = " << Ab[0].address_size() << std::endl;
    std::cout << "Address of Ab[0].type = " << Ab[0].address_type() << std::endl;
    std::cout << "Address of Ab[1] = " << int(&Ab[1]) << std::endl;

    system("pause");
    return 0;
}