C++必修：类与对象(二)

2024-06-04 9093阅读

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1. 构造函数

1.1. 定义

构造函数是一个特殊的成员函数，名字与类名相同, 创建类类型对象时由编译器自动调用，以保证每个数据成员都有一个合适的初始值，并且在对象整个生命周期内只调用一次。其特点如下：

函数名与类名相同。
无返回值。
对象实例化时编译器自动调用对应的构造函数。
构造函数可以重载。

下面是一个日期类的构造函数

class Date
{
public:
	Date(int year, int month, int day)
	{
		_year = year;
		_month = month;
		_day = day;
	}
	void Print()
	{
		cout 
	Date d1(1,1,1);//自动调用
	d1.Print();
	return 0;
}

public:
	/*Date(int year, int month, int day)
	{
		_year = year;
		_month = month;
		_day = day;
	}*/
    //编译器会自动生成一个无参的默认构造函数
	void Print()
	{
		cout 
public:
	Date()//无参
	{
		_year = 1900;
		_month = 1;
		_day = 1;
	}
	Date(int year = 1900, int month = 1, int day = 1)//全缺省
	{
		_year = year;
		_month = month;
		_day = day;
	}
	void Print()
	{
		cout 
	Date d;//引起歧义
	return 0;
}

public:
	Betty()
	{
		cout 
public:
	void Print()
	{
		cout 
	Date d;
	d.Print();
	return 0;
}

public:
	void Print()
	{
		cout 
	Date d;
	d.Print();
	return 0;
}

public:
	Date(int year, int month, int day)
		: _year(year)
		, _month(month)
		, _day(day)
	{
	 //...
	}
	void Print()
	{
		cout 
	Date d(2024,1,3);
	d.Print();
	return 0;
}

public:
	A(int a)
		:_a(a)
	{}
private:
	int _a;
};
class B
{
public:
	B(int a, int ref)
		:_b(a)
		, _ref(ref)
		, _n(3)
	{}
private:
	A _b; // 没有默认构造函数
	int& _ref; // 引用
	const int _n; // const常量
};

public:
	A(int a = 1)//默认构造
		:_a(a)
	{
		cout 
public:
	B(int a)
		:_m(a)
	{}
private:
	int _m;
	A _b; 
};
int main()
{
	B b(2);
	return 0;
}

public:
	A(int a)
		:_a1(a)
		, _a2(_a1)
	{}
	void Print() 
	{
		cout 
	A aa(1);
	aa.Print();
}//输出？？

public:
	//构造函数
	Date(int year = 1, int month = 1, int day = 1)
	{
		_year = year;
		_month = month;
		_day = day;
	}
	void Print()
	{
		cout 
		_year = _month = _day = 0;
	}
private:
	int _year;
	int _month;
	int _day;
};

public:
	//构造函数
	Date(int year = 1, int month = 1, int day = 1)
	{
		_year = year;
		_month = month;
		_day = day;
	}
	void Print()
	{
		cout 
public:
	~Betty()
	{
		cout 
public:
	//构造函数
	Date(int year = 1, int month = 1, int day = 1)
	{
		_year = year;
		_month = month;
		_day = day;
	}
	void Print()
	{
		cout 
public:
	Stack(size_t capacity = 2)
	{
		_array = (DataType*)malloc(sizeof(DataType) * capacity);
		if (nullptr == _array)
		{
			perror("malloc申请空间失败!!!");
			return;
		}
		_capacity = capacity;
		_size = 0;
	}
	void Push(DataType data)
	{
		// CheckCapacity();
		_array[_size] = data;
		_size++;
	}
	~Stack()
	{
		if (_array!=nullptr)
		{
			free(_array);
			_array = nullptr;
			_capacity = 0;
			_size = 0;
		}
	}
private:
	DataType* _array;
	int _capacity;
	int _size;
};

public:
	Date(int year = 1900, int month = 1, int day = 1)
	{
		_year = year;
		_month = month;
		_day = day;
	}
	Date(const Date& d) 
	{
		_year = d._year;
		_month = d._month;
		_day = d._day;
	}
private:
	int _year;
	int _month;
	int _day;
};
int main()
{
	Date d1(2024,2,2);
	Date d2(d1);//拷贝构造
	Date d3 = d1;//拷贝构造
    d1.Print();
	d2.Print();
	d3.Print();
	return 0;
}

		_year = d._year;
		_month = d._month;
		_day = d._day;
	}

public:
	Date(int year = 1900, int month = 1, int day = 1)
	{
		_year = year;
		_month = month;
		_day = day;
	}
	//Date(const Date& d)
	//{
	//	_year = d._year;
	//	_month = d._month;
	//	_day = d._day;
	//}
	void Print()
	{
		cout 
	Date d1(2024, 2, 2);
	Date d2(d1);//拷贝构造
	Date d3 = d1;//拷贝构造
	d1.Print();
	d2.Print();
	d3.Print();
	return 0;
}

public:
	Stack(size_t capacity = 10)
	{
		_array = (DataType*)malloc(capacity * sizeof(DataType));
		if (nullptr == _array)
		{
			perror("malloc申请空间失败");
			return;
		}
		_size = 0;
		_capacity = capacity;
	}
	void Push(const DataType& data)
	{
		// CheckCapacity();
		_array[_size] = data;
		_size++;
	}
	~Stack()
	{
		if (_array)
		{
			free(_array);
			_array = nullptr;
			_capacity = 0;
			_size = 0;
		}
	}
private:
	DataType* _array;
	size_t _size;
	size_t _capacity;
};
int main()
{
	Stack s1;
	s1.Push(1);
	s1.Push(2);
	s1.Push(3);
	s1.Push(4);
	Stack s2(s1);//默认拷贝构造
	return 0;
}

public:
	Date(int year, int month, int day)
		: _year(year)
		, _month(month)
		, _day(day)
	{
	 //...
	}
	void Print()
	{
		cout 
	return d1._year == d2._year
		&& d1._month == d2._month
		&& d1._day == d2._day;
}
int main()
{
	Date d1(2024,1,1);
	Date d2(2024, 1, 1);
	if (d1 == d2)//也可以显示调用operator==(d1,d2);
	{
		cout 
		cout 
	return _year == d._year
		&& _month == d._month
		&& _day == d._day;
}

public:
	Date(int year = 1900, int month = 1, int day = 1)
	{
		_year = year;
		_month = month;
		_day = day;
	}
	Date& operator=(const Date& d)//赋值运算符重载
	{
		if (this != &d)
		{
			_year = d._year;
			_month = d._month;
			_day = d._day;
		}
		return *this;
	}
private:
	int _year;
	int _month;
	int _day;
};

public:
	Time()
	{
		_hour = 1;
		_minute = 1;
		_second = 1;
	}
	Time& operator=(const Time& t)
	{
		cout 
			_hour = t._hour;
			_minute = t._minute;
			_second = t._second;
		}
		return *this;
	}
private:
	int _hour;
	int _minute;
	int _second;
};
class Date
{
private:
	// 基本类型(内置类型)
	int _year = 2024;
	int _month = 1;
	int _day = 1;
	// 自定义类型
	Time _t;
};
int main()
{
	Date d1;
	Date d2;
	d1 = d2;
	return 0;
}

public:
	Date(int year = 1900, int month = 1, int day = 1)
	{
		_year = year;
		_month = month;
		_day = day;
	}
	int _year;
	int _month;
	int _day;
};
Date& operator=(Date& left, const Date& right)//error
{
	if (&left != &right)
	{
		left._year = right._year;
		left._month = right._month;
		left._day = right._day;
	}
	return left;
}

public:
	Date(int year, int month, int day)
	{
		_year = year;
		_month = month;
		_day = day;
	}
	void Print()
	{
		cout 
	const Date d2(2022, 1, 13);
	d2.Print();//error
	return 0;
}

		cout 
public:
	Date* operator&()
	{
		return this;
	}
	const Date* operator&()const
	{
		return this;
	}
private:
	int _year; // 年
	int _month; // 月
	int _day; // 日
};