【C/C++】类和对象（上）：（二）实例化——类实例化出对象，对象大小，this指针，对比C++/C两种语言实现Stack

#include<iostream>
using namespace std;

class Stack
{
public:
	//成员函数
	void Init(int n = 4)
	{
		//...
	}

private:
	//成员变量，声明
	int* array;
	size_t capacity;
	size_t top;
};

int main()
{
	//定义，类实例化对象
	Stack s1;
	s1.top = 0;
	s1.Init();

	Stack s2;
	s2.top = 1;
	s2.Init(100);

	cout << sizeof(s1) << endl;
	cout << sizeof(Stack) << endl;

	return 0;
}

#include<iostream>
using namespace std;

class A
{
public:
	void Print()
	{
		cout << _ch << endl;
	}
private:
	char _ch;
	int _i;
};

class B
{
public:
	void Print()
	{
		//...
	}
};

class C
{ };

int main()
{
	cout << sizeof(A) << endl;
	//开1个byte的空间是为了占位，占位不存储实际数据，表达对象存在过(占位标识对象存在)
	cout << sizeof(B) << endl;
	cout << sizeof(C) << endl;

	B b1;
	B b2;
	cout << &b1 << endl;
	cout << &b2 << endl;

	return 0;
}

class Date
{
public:
	//void Init(int* const year, int month, int day)
	void Init(int year, int month, int day)
	{
		/*cout << this << endl;*/

		//const保护this不能修改
		//this = nullptr;
		
		//this->_year = year;
		this->_year = year;
		this->_month = month;
		_day = day;
	}

	void Print()
	{
		cout << _year << "/" << _month << "/" << _day << endl;
	}
private:
	//这里只是声明，没有开空间
	int _year;
	int _month;
	int _day;
};

int main()
{
	Date d1;
	Date d2;
	//d1.Init(&d1, 2025, 7, 31);
	d1.Init(2025, 7, 31);

	//d2.Init(&d2, 2025, 7, 31);
	d2.Init(2025, 7, 31);

	d1.Print();
	d2.Print();

	return 0;
}

#define  _CRT_SECURE_NO_WARNINGS  1

#include<stdio.h>
#include<stdlib.h>
#include<stdbool.h>
#include<assert.h>
typedef int STDataType;
typedef struct Stack
{
	STDataType* a;
	int top;
	int capacity;
}ST;
void STInit(ST* ps)
{
	assert(ps);
	ps->a = NULL;
	ps->top = 0;
	ps->capacity = 0;
}
void STDestroy(ST* ps)
{
	assert(ps);
	free(ps->a);
	ps->a = NULL;
	ps->top = ps->capacity = 0;
}
void STPush(ST* ps, STDataType x)
{
	assert(ps);
	// 满了， 扩容
	if (ps->top == ps->capacity)
	{
		int newcapacity = ps->capacity == 0 ? 4 : ps->capacity * 2;
		STDataType* tmp = (STDataType*)realloc(ps->a, newcapacity *
			sizeof(STDataType));
		if (tmp == NULL)
		{
			perror("realloc fail");
			return;
		}
		ps->a = tmp;
		ps->capacity = newcapacity;
	}
	ps->a[ps->top] = x;
	ps->top++;
}

bool STEmpty(ST* ps)
{
	assert(ps);
	return ps->top == 0;
}

void STPop(ST* ps)
{
	assert(ps);
	assert(!STEmpty(ps));
	ps->top--;
}

STDataType STTop(ST* ps)
{
	assert(ps);
	assert(!STEmpty(ps));
	return ps->a[ps->top - 1];
}

int STSize(ST* ps)
{
	assert(ps);
	return ps->top;
}

int main()
{
	ST s;
	STInit(&s);
	STPush(&s, 1);
	STPush(&s, 2);
	STPush(&s, 3);
	STPush(&s, 4);
	while (!STEmpty(&s))
	{
		printf("%d\n", STTop(&s));
		STPop(&s);
	}
	STDestroy(&s);
	return 0;
}

#define  _CRT_SECURE_NO_WARNINGS  1

#include<iostream>
#include<assert.h>
using namespace std;
typedef int STDataType;
class Stack
{
public:
	// 成员函数 
	void Init(int n = 4)
	{
		_a = (STDataType*)malloc(sizeof(STDataType) * n);
		if (nullptr == _a)
		{
			perror("malloc申请空间失败");
			return;
		}
		_capacity = n;
		_top = 0;
	}

	void Push(STDataType x)
	{
		if (_top == _capacity)
		{
			int newcapacity = _capacity * 2;
			STDataType* tmp = (STDataType*)realloc(_a, newcapacity *
				sizeof(STDataType));
			if (tmp == NULL)
			{
				perror("realloc fail");
				return;
			}
			_a = tmp;
			_capacity = newcapacity;
		}
		_a[_top++] = x;
	}
	void Pop()
	{
		assert(_top > 0);
		--_top;
	}
	bool Empty()
	{
		return _top == 0;
	}
	int Top()
	{
		assert(_top > 0);
		return _a[_top - 1];
	}
	void Destroy()
	{
		free(_a);
		_a = nullptr;
		_top = _capacity = 0;
	}
private:
	// 成员变量 
	STDataType* _a;
	size_t _capacity;
	size_t _top;
};
int main()
{
	Stack s;
	s.Init();
	s.Push(1);
	s.Push(2);
	s.Push(3);
	s.Push(4);
	while (!s.Empty())
	{
		printf("%d\n", s.Top());
		s.Pop();
	}
	s.Destroy();
	return 0;
}

#define  _CRT_SECURE_NO_WARNINGS  1

#include<iostream>
using namespace std;

class Stack
{
public:
	//成员函数
	void Init(int n = 4)
	{
		//...
	}

//private:
	//成员变量，声明
	int* array;
	size_t capacity;
	size_t top;
};

int main()
{
	//定义，类实例化对象
	Stack s1;
	s1.top = 0;
	s1.Init();

	Stack s2;
	s2.top = 1;
	s2.Init(100);

	cout << sizeof(s1) << endl;
	cout << sizeof(Stack) << endl;

	return 0;
}

class A
{
public:
	void Print()
	{
		cout << _ch << endl;
	}
private:
	char _ch;
	int _i;
};

class B
{
public:
	void Print()
	{
		//...
	}
};

class C
{ };

int main()
{
	cout << sizeof(A) << endl;
	//开1个byte的空间是为了占位，占位不存储实际数据，表达对象存在过(占位标识对象存在)
	cout << sizeof(B) << endl;
	cout << sizeof(C) << endl;

	B b1;
	B b2;
	cout << &b1 << endl;
	cout << &b2 << endl;

	return 0;
}

class Date
{
public:
	//void Init(int* const year, int month, int day)
	void Init(int year, int month, int day)
	{
		/*cout << this << endl;*/

		//const保护this不能修改
		//this = nullptr;
		
		//this->_year = year;
		this->_year = year;
		this->_month = month;
		_day = day;
	}

	void Print()
	{
		cout << _year << "/" << _month << "/" << _day << endl;
	}
private:
	//这里只是声明，没有开空间
	int _year;
	int _month;
	int _day;
};

int main()
{
	Date d1;
	Date d2;
	//d1.Init(&d1, 2025, 7, 31);
	d1.Init(2025, 7, 31);

	//d2.Init(&d2, 2025, 7, 31);
	d2.Init(2025, 7, 31);

	d1.Print();
	d2.Print();

	return 0;
}

class A
{
public:
	void Print()
	{
		cout << this << endl;
		cout << "A::Print()" << endl;
		cout << _a << endl;
	}
private:
	int _a;
};

int main()
{
	A* p = nullptr;
	//p->Print(); // call 函数地址

	(*p).Print();

	// 00C3210C  mov       ecx,dword ptr[p]
	// 00C3210F  call      A::Print(0C31447h)

	return 0;
}