概述

#pragma pack(4)

class CAnimal
{
public:
    char name[3];
    short age;
    int color;
    char gender;
};

class CDog : public CAnimal
{
public:
    int hurt;
};

void mem_offset()
{
    CAnimal animal;
    CDog dog;
    
    cout << "-----animal-----" << endl;
    cout << "sizeof(animal) = " << sizeof(animal) << endl;
    cout << "name offset = " << (char*)animal.name - (char*)&animal << endl;
    cout << "age offset = " << (char*)&animal.age - (char*)&animal << endl;
    cout << "color offset = " << (char*)&animal.color - (char*)&animal << endl;
    cout << "gender offset = " << (char*)&animal.gender - (char*)&animal << endl;
    
    cout << "-----dog-----" << endl;
    cout << "sizeof(dog) = " << sizeof(dog) << endl;
    cout << "name offset = " << (char*)dog.name - (char*)&dog << endl;
    cout << "age offset = " << (char*)&dog.age - (char*)&dog << endl;
    cout << "color offset = " << (char*)&dog.color - (char*)&dog << endl;
    cout << "gender offset = " << (char*)&dog.gender - (char*)&dog << endl;
    cout << "hurt offset = " << (char*)&dog.hurt - (char*)&dog << endl;
}
 

-----animal-----
sizeof(animal) = 16
name offset = 0
age offset = 4
color offset = 8
gender offset = 12
-----dog-----
sizeof(dog) = 20
name offset = 0
age offset = 4
color offset = 8
gender offset = 12
hurt offset = 16

• 每個類會生成對應的c struct，c struct中的資料成員在記憶體中佈局順序與資料成員在類定義中的順序一致
• 子類的c struct在父類的c struct末尾新增自身的資料成員

類隱式轉換

class CAnimal
{
public:
    CAnimal()
    {
        cout << "CAnimal()" << endl;
    }
    
    CAnimal(const CAnimal &other)
    {
        cout << "CAnimal(const CAnimal &other)" << endl;
    }
    
public:
    CAnimal& operator=(const CAnimal &other)
    {
        cout << "CAnimal operator=" << endl;
        return *this;
    }
    
public:
    void info()
    {
        cout << "CAnimal info()" << endl;
    }
};

class CDog : public CAnimal
{
public:
    CDog()
    {
        cout << "CDog()" << endl;
    }
    
    CDog(const CDog &other) : CAnimal(other)
    {
        cout << "CDog(const CDog &other)" << endl;
    }
    
public:
    CDog& operator=(const CDog &other)
    {
        CAnimal::operator=(other);
        cout << "CDog operator=" << endl;
        return *this;
    }
};

void class_convert()
{
    CDog dog;
    
    CAnimal* pAnimal = &dog;
    CAnimal* rAnimal = &dog;
    
    pAnimal->info();
    rAnimal->info();
    
    CAnimal animal = dog;
    animal = dog;
}
 

CAnimal()
CDog()
CAnimal info()
CAnimal info()
CAnimal(const CAnimal &other)
CAnimal operator=

• 子類物件初始化父類物件的本質是呼叫父類的複製建構函式
• 子類物件賦值給父類物件的本質是呼叫父類的賦值操作符函式