C++内存管理

#include<iostream>
using namespace std;
int main()
{
	int a = 3;
	int b = 4;
	int c = 5;
	int d = 6;
	cout <<"a:"<< &a << endl;
	cout << "b:"<<&b << endl;
	cout << "c:"<<&c << endl;
	cout << "d:"<<&d << endl;
	return 0;
}

#include<iostream>
using namespace std;
int main()
{
	int num = 10;
	while (num--)
	{
		int *p1 = (int*)malloc(sizeof(int));
		int *p2 = (int*)malloc(sizeof(int));
		cout <<"p1"<< p1 << endl;
		cout <<"p2"<<p2 << endl;
		cout << endl;
		free(p1);
	}
	return 0;
}

//C++开辟动态内存的新玩法
//语法演示：
#include<iostream>
using namespace std;
int main()
{
	//申请一个int的动态空间
	int* p1 = (int*)malloc(sizeof(int));
	*p1 = 1;
	int* p2 = new int(2);//这里是初始化
	free(p1);
	delete p2;
	//申请一个10各int的动态数组
	int *p3 = (int*)malloc(sizeof(int)* 10);
	for (int i = 0; i < 10; i++)
	{
		p3[i] = i + 1;
	}
	int *p4 = new int[10]{1, 2, 3, 4, 5, 6, 7, 8, 9, 10};//初始化
	free(p3);
	delete[]p4;
	return 0;
}

#include<iostream>
using namespace std;
struct ListNode
{
	int _val;
	ListNode* _next;
	ListNode* _prev;
	//构造函数
	ListNode(int val = 0)
	:_val(val)
	, _next(nullptr)
	, _prev(nullptr)
	{
        cout<<"ListNode(int val = 0)"<<endl;
    }
	~ListNode()
	{
		cout << "ListNode()" << endl;
	}
};
int main()
{
	//申请一个结点的空间
    ListNode* pa = (ListNode*)malloc(sizeof(ListNode)*4);
	ListNode* pb = new ListNode(1);//不用去用sizeof去计算空间大小，很方便   
	free(pa);
	delete pb;
	//申请4个结点的空间--当然了一般不会这么玩儿，我们只是看看效果
	ListNode* pc = (ListNode*)malloc(sizeof(ListNode)* 4);
	ListNode* pd = new ListNode[4]{1, 2, 3, 4};
	free(pc);
	delete[]pd;
	return 0;
}

struct ListNode
{
	int _val;
	ListNode* _next;
	ListNode* _prev;
	//构造函数
	ListNode(int val = 0)
		:_val(val)
		, _next(nullptr)
		, _prev(nullptr)
	{
		cout << "ListNode(int val = 0)" << endl;
	}
	~ListNode()
	{
		cout << "ListNode()" << endl;
	}
};
void f()
{
	// 他的用法跟malloc和free是完全一样的，功能都是在堆上申请释放空间
	// 失败了处理方式不一样，malloc失败返回NULL，operator new失败以后抛异常
	ListNode* p1 = (ListNode*)malloc(sizeof(ListNode));
	free(p1);
	ListNode* p2 = (ListNode*)operator new(sizeof(ListNode));
	operator delete(p2);
	void* p3 = malloc(0x7fffffff);
	if (p3 == NULL)
	{
		cout << "malloc fail" << endl;
	}
	void* p4 = operator new(0x7fffffff);
	ListNode* p5 = new ListNode(2);
	cout << "继续" << endl;
}
//
//
int main()
{
	try
	{
		f();
	}
	catch (exception& e)
	{
		cout << e.what() << endl;
	}
	return 0;
}

struct ListNode//目的是提高效率
{
	ListNode* _next;
	ListNode* _prev;
	int _val;
	// 类中重载专属operator new
	void* operator new(size_t n)
	{
	void* p = nullptr;
	p = allocator<ListNode>().allocate(1);
	cout << "memory pool allocate" << endl;
	return p;
	}
	void operator delete(void* p)
	{
		allocator<ListNode>().deallocate((ListNode*)p, 1);
		cout << "memory pool deallocate" << endl;
	}
	ListNode(int val)
		:_next(nullptr)
		, _prev(nullptr)
		, _val(val)
	{}
};
int main()
{
	ListNode* p = new ListNode(1);
	delete p;
	return 0;
}

class A
{
public:
	A(int a = 0)
		:_a(a)
	{
		cout << "A(int a = 0)" << endl;
	}
	~A()
	{
		cout << "~A()" << endl;
	}
private:
	int _a;
};
int main()
{
	A* pa = (A*)operator new(sizeof(A));
	//pa->A();//error错误调用方式，构造函数只允许构造时进行调用
	new(pa)A; // 定位new，placement-new，显示调用构造函数初始化这块对象空间
	A* pb = (A*)operator new(sizeof(A));
	new(pb)A(3);
    A* pc = new A;
	new(pc)A(3);
	// 等于 delete p
	pa->~A(); // 析构函数可以显示调用
	operator delete(pa);
	pb->~A();
	operator delete(pb);
    delete pc;
	return 0;
}