【C++初阶路】--- 类和对象(中)

class Date
{
public:
	//void InitDate(Date* const this, int year = 2024, int month = 6, int day = 14)
	void InitDate(int year = 2024, int month = 6, int day = 14)
	{
		_year = year;
		_month = month;
		_day = day;
	}

	//void PrintDate(Date* const this);
	void PrintDate()
	{
		cout << _year << "-" << _month << "-" << _day << endl;
	}

private:
	int _year;
	int _month;
	int _day;
};

int main()
{
	Date d1;
	Date d2;
	//d1.InitDate(&d1);
	d1.InitDate();
	d2.InitDate(2024, 6, 17);
	d1.PrintDate();
	d2.PrintDate();

	return 0;
}

class A
{
public:
	void Print()
	{
		cout << "Print()" << endl;
	}
private:
	int _a;
};
int main()
{
	A* p = nullptr;
	p->Print();
	//(*p).PrintA(); ---- question 2
	return 0;
}

 // 1.下面程序编译运行结果是？  A、编译报错  B、运行崩溃  C、正常运行
class A
{
public:
	//void PrintA(A* const this)
    void PrintA()
    {
    	//cout << this->_a << endl;
        cout << _a << endl;
    }
private:
    int _a;
};
int main()
{
    A* p = nullptr;
    p->PrintA();
    return 0;
}

typedef int DataType;
typedef struct Stack
{
	DataType* array;
	int capacity;
	int size;
}Stack;
void StackInit(Stack* ps)
{
	assert(ps);
	ps->array = (DataType*)malloc(sizeof(DataType) * 3);
	if (NULL == ps->array)
	{
		assert(0);
		return;
	}
	ps->capacity = 3;
	ps->size = 0;
}
void StackDestroy(Stack* ps)
{
	assert(ps);
	if (ps->array)
	{
		free(ps->array);
		ps->array = NULL;
		ps->capacity = 0;
		ps->size = 0;
	}
}

void CheckCapacity(Stack* ps)
{
	if (ps->size == ps->capacity)
	{
		int newcapacity = ps->capacity * 2;
		DataType* temp = (DataType*)realloc(ps->array,
			newcapacity * sizeof(DataType));
		if (temp == NULL)
		{
			perror("realloc申请空间失败!!!");
			return;
		}
		ps->array = temp;
		ps->capacity = newcapacity;
	}
}

void StackPush(Stack* ps, DataType data)
{
	assert(ps);
	CheckCapacity(ps);
	ps->array[ps->size] = data;
	ps->size++;
}
int StackEmpty(Stack* ps)
{
	assert(ps);
	return 0 == ps->size;
}
void StackPop(Stack* ps)
{
	if (StackEmpty(ps))
		return;
	ps->size--;
}

DataType StackTop(Stack* ps)
{
	assert(!StackEmpty(ps));
	return ps->array[ps->size - 1];
}
int StackSize(Stack* ps)
{
	assert(ps);
	return ps->size;
}
int main()
{
	Stack s;
	StackInit(&s);
	StackPush(&s, 1);
	StackPush(&s, 2);
	StackPush(&s, 3);
	StackPush(&s, 4);
	printf("%d\n", StackTop(&s));
	printf("%d\n", StackSize(&s));
	StackPop(&s);
	StackPop(&s);
	printf("%d\n", StackTop(&s));
	printf("%d\n", StackSize(&s));
	StackDestroy(&s);
	return 0;
}

typedef int DataType;
class Stack
{
public:
	void Init()
	{
		_array = (DataType*)malloc(sizeof(DataType) * 3);
		if (nullptr == _array)
		{
			perror("malloc申请空间失败!!!");
			return;
		}
		_capacity = 3;
		_size = 0;
	}
	void Push(DataType data)
	{
		CheckCapacity();
		_array[_size] = data;
		_size++;
	}
	void Pop()
	{
		if (Empty())
			return;
		_size--;
	}
	DataType Top() { return _array[_size - 1]; }
	int Empty() { return 0 == _size; }
	int Size() { return _size; }
	void Destroy()
	{
		if (_array)
		{
			free(_array);
			_array = nullptr;
			_capacity = 0;
			_size = 0;
		}
	}
private:
	void CheckCapacity()
	{
		if (_size == _capacity)
		{
			int newcapacity = _capacity * 2;
			DataType* temp = (DataType*)realloc(_array, newcapacity *
				sizeof(DataType));
			if (temp == nullptr)
			{
				perror("realloc申请空间失败!!!");
				return;
			}
			_array = temp;
			_capacity = newcapacity;
		}
	}
private:
	DataType* _array;
	int _capacity;
	int _size;
};
int main()
{
	Stack s;
	s.Init();
	s.Push(1);
	s.Push(2);
	s.Push(3);
	s.Push(4);
	printf("%d\n", s.Top());
	printf("%d\n", s.Size());
	s.Pop();
	s.Pop();
	printf("%d\n", s.Top());
	printf("%d\n", s.Size());
	s.Destroy();
	return 0;
}

class Date{};

class Date
{
public:
	//1. 无参构造函数
	Date()
	{}

	//2. 带参构造函数
	Date(int year, int month, int day)
	{
		_year = year;
		_month = month;
		_day = day;
	}

private:
	int _year;
	int _month;
	int _day;
};

void TestDate()
{
	Date d1; // 调用无参构造函数
	Date d2(2024, 6, 19); // 调用带参的构造函数
	// 注意：如果通过无参构造函数创建对象时，对象后面不用跟括号，否则就成了函数声明
	// 以下代码的函数：声明了d3函数，该函数无参，返回一个日期类型的对象
	// warning C4930: “Date d3(void)”: 未调用原型函数(是否是有意用变量定义的?)
	Date d3();
}

class Date
{
public:
	/*
	// 如果用户显式定义了构造函数，编译器将不再生成
   Date(int year, int month, int day)
	{
		_year = year;
		_month = month;
		_day = day;
	}
	*/
	void Print()
	{
		cout << _year << "-" << _month << "-" << _day << endl;
	}

private:
	int _year;
	int _month;
	int _day;
};

int main()
{
	Date d1;
	return 0;
}

将Date类中构造函数屏蔽后，代码可以通过编译，因为编译器生成了一个无参的默认构造函数；
将Date类中构造函数放开，代码编译失败，因为一旦显式定义任何构造函数，编译器将不再生成；
无参构造函数，放开后报错：error C2512: “Date”: 没有合适的默认构造函数可用。

class Time
{
public:
	Time(int hour = 24, int minute = 0, int second = 0)
	{
		cout << "构造函数：Time()" << endl;
		_hour = hour;
		_minute = minute;
		_second = second;
	}
private:
	int _hour;
	int _minute;
	int _second;
};

class Date
{
public:
	void Print()
	{
		cout << _year << "-" << _month << "-" << _day << endl;
	}
private:
	//基本类型（内置类型） -> 随机值
	int _year;
	int _month;
	int _day;

	//C++11以后版本，可以在成员变量声明时给默认值！！
	//int _year = 2024;
	//int _month = 6;
	//int _day = 19;

	//自定义类型  -> 调用自己的默认成员函数
	Time _t;
};

int main()
{
	Date d1;
	d1.Print();
	return 0;
}

class Date
{
public:
	Date()
	{
		_year = 1900;
		_month = 1;
		_day = 1;
	}
	Date(int year = 2024, int month = 5, int day = 9)
	{
		_year = year;
		_month = month;
		_day = day;
	}
private:
	int _year;
	int _month;
	int _day;
};
// 以下测试函数能通过编译吗？
int main()
{
	Date d1;
	return 0;
}