1、C/C++内存分布

在这里插入图片描述

2、C语言中动态内存管理方式：malloc/calloc/realloc/free

void Test ()
{
	int* p1 = (int*) malloc(sizeof(int));
	free(p1);
	
	//【1】malloc/calloc/realloc的区别是什么？【calloc = malloc + memset】
	int* p2 = (int*)calloc(4, sizeof (int));
	int* p3 = (int*)realloc(p2, sizeof(int)*10);
	
	//【2】这里需要free(p2)吗？【不需要】
	free(p3);
}

3、C++内存管理方式

int main()
{
	//单个对象
	int* p1 = (int*)malloc(sizeof(int));
	int* p2 = new int; //自动计算大小，不需要强转

	//多个对象
	int* p3 = (int*)malloc(sizeof(int) * 10);
	int* p4 = new int[10];

	free(p1);
	free(p3);

	delete p2;
	delete[] p4;

	//额外支持了开空间+初始化
	int* p5 = new int(1);
	int* p6 = new int[10] {1, 2, 3};
	int* p7 = new int[10] {};

	delete p5;
	delete[] p6;
	delete[] p7;

	return 0;
}

class A
{
public:
	A(int a = 0)
		: _a(a)
	{
		cout << "A():" << this << endl;
	}

	~A()
	{
		cout << "~A():" << this << endl;
	}

private:
	int _a;
};

struct ListNode
{
	ListNode* _next;
	int _val;

	ListNode(int val = 0)
		:_val(0)
		, _next(nullptr)
	{}
};

int main()
{
	//malloc没有办法很好支持动态申请的自定义对象初始化
	A* p1 = (A*)malloc(sizeof(A));
	//p1->_a = 0;
	//p1->A(1);

	//自定义类型，开空间+调用构造函数初始化
	A* p2 = new A;
	A* p3 = new A(3);

	//自定义类型，调用析构函数+释放空间
	delete p2;
	delete p3;

	A* p4 = new A[10];
	delete[] p4;

	A aa1;
	A aa2;
	A* p5 = new A[10]{ aa1,aa2 }; //有名对象
	delete[] p5;

	A* p6 = new A[10]{ A(1),A(2) }; //匿名对象
	delete[] p6;

	A* p7 = new A[10]{ 1,2 }; //隐式类型转换

	ListNode* n1 = new ListNode(1);
	ListNode* n2 = new ListNode(2);
	ListNode* n3 = new ListNode(3);
	ListNode* n4 = new ListNode(4);
	ListNode* n5 = new ListNode(5);

	n1->_next = n2;
	n2->_next = n3;
	n3->_next = n4;
	n4->_next = n5;

	delete n1;
	delete n2;
	delete n3;
	delete n4;
	delete n5;

	return 0;
}

4、operator new与operator delete 函数

5、new和delete的实现原理

【1】内置类型

【2】自定义类型

6、定位new表达式（placement-new）

#define _CRT_SECURE_NO_WARNINGS 1
#include <iostream>
using namespace std;

class A
{
public:
	A(int a = 0)
		:_a(a)
	{
		cout << "A()" << endl;
	}
	~A()
	{
		cout << "~A()" << endl;
	}
private:
	int _a;
};

int main()
{
	//new
	A* p1 = (A*)operator new(sizeof(A)); //只开空间，没初始化
	//p1->A(2); //error【不能显示调用构造函数】
	new(p1)A(2); //【定位new，可以显式调用构造函数】
	
	//delete
	p1->~A(); //【可以显式调用析构函数】
	operator delete (p1);

	return 0;
}