题目为 Rectangle 类实现构造函数,拷贝构造函数,赋值操作符,析构函数。
class Shape
{
int no;
};
class Point
{
int x;
int y;
};
class Rectangle: public Shape
{
int width;
int height;
Point * leftUp;
public:
Rectangle(int width, int height, int x, int y);
Rectangle(const Rectangle& other);
Rectangle& operator=(const Rectangle& other);
~Rectangle();
};
设计思路
01. Big Three Function Design - 三大函数设计
1.1 General Constructor - 构造函数
-
private could be omit at the begging of a class.
class MyClass
{
// for private variables
public:
// for public interface
protected:
// for protected functions
}
- We would prefer to use
this
Rectangle(int width, int height)
{
this->width = width;
this->height = height;
}
- There is a
point-to-class pointer and how to build a constructor
// Class
class Point
{
int x;
int y;
public:
Point (int x = 0, int y =0)
{
this->x = x;
this->y = y;
}
int get_x() const {return x;}
int get_y() const {return y;}
};
class Rectangle: public Shape
{
int width;
int height;
Point* leftUp;
public:
Rectangle(int width, int height, int x, int y);
...
};
// Constructor
Rectangle::Rectangle(int width, int height, int x, int y)
{
this->width = width;
this->height = height;
this->leftUp = new Point(x, y);
}
1.2 Copy Constructor
- Step 1: 父类Shape的创建在函数列表中完成，不能使用
this->no进行处理。
- Step 2: 子类的non-pointer成员，也可以在函数列表中完成
- Step 3: 子类的pointer成员，必须先检查是否为
nullptr，在依次进行赋值，即深拷贝。
Rectangle::Rectangle(const Rectangle& other):
Shape(other), // Step 1: father class member
width_(other.width_), // Step 2: non-pointer member
height_(other.height_)
{
if (other.leftUp_ != nullptr) // Step 3: Check whether other is nullptr
{
this->leftUp_ = new Point(*(other.leftUp_)); // Point copy constructor; other.leftUp_ is a (Point* ); so *(other.leftUp_) is a Point.
}
else
this->leftUp_= nullptr;
}
1.3 Copy Assignment
- Step 1：先检查是否是
self-assignment
- Step 2：父类程序按的处理。（这里经过查询书籍，可以知道，直接使用系统默认的copy assignment函数即可完成任务）
- Step 3：子类non-pointer成员直接赋值
- Step 4：检查pointer等号左右两侧是否为nullptr，并分别处理
Rectangle& Rectangle::operator=(const Rectangle& other)
{
if (this == &other) // Step 1: Self Assignment Check
{
return *this;
}
Shape::operator=(other); // Step 2: Default copy assignment
this->width_ = other.width_; // Step 3: General member variables copy
this->height_ = other.height_;
if( other.leftUp_ != nullptr ) // Step 4: Check pointer member
{
if( this->leftUp_ != nullptr )
{
*(this->leftUp_) = *(other.leftUp_);
}
else
{
this->leftUp_ = new Point(*other.leftUp_);
}
}
else
{
delete this->leftUp_;
this->leftUp_ = nullptr;
}
return *this;
}
1.4 Destructor
- General idea is to delete the pointer directly.
Rectangle::~Rectangle()
{
delete leftUp;
}
Rectangle::~Rectangle()
{
delete leftUp; // Just release the memory space, but not the value is still an address
leftUp = nullptr;
}
1.5 inline function
- The body of an
inline fucntion should be in the .h file, otherwise you will get
undefined reference to
总结
- 首先理清类之间的相互关系，一边后续设计三大函数时，明白各个类成员的来历。
- 严格按照既定的设计思路书写，不能随心所欲，以免漏写或画蛇添足。
- 处理指针问题要格外小心。
Reference
