c++(内存管理)_c++内存管理

目录

一.c++内存分布

二.c++内存管理方式

三.operator new与operator delete函数

四.malloc/free和new/delete的区别

五.定位new表达式(placement-new)(构造函数)

一.c++内存分布

二.c++内存管理方式

自定义类型调用构造函数和析构函数 

抛异常用try/catch

三.operator new与operator delete函数

1.内置类型：

申请的是内置类型的空间，new和malloc，delete和free基本类似，不同的地方是：new/delete申请和 释放的是单个元素的空间，new[]和delete[]申请的是连续空间，而且new在申请空间失败时会抛异常， malloc会返回NULL

#include"iostream"
using namespace std;
int main()
{
	
	int* p1 = new int;
	free(p1);//内置类型用free与new配套不会造成内存泄漏
 
	return 0;
}

#include"iostream"
using namespace std;
class A
{
public:
	A(int a1 = 0, int a2 = 0)
		:_a1(a1)
		, _a2(a2)
	{
		cout << "A(int a1 = 0, int a2 = 0)" << endl;
	}
 
	A(const A& aa)
		:_a1(aa._a1)
	{
		cout << "A(const A& aa)" << endl;
	}
 
	A& operator=(const A& aa)
	{
		cout << "A& operator=(const A& aa)" << endl;
		if (this != &aa)
		{
			_a1 = aa._a1;
		}
		return *this;
	}
 
	~A()
	{
		//delete _ptr;
		cout << "~A()" << endl;
	}
 
	void Print()
	{
		cout << "A::Print->" << _a1 << endl;
	}
 
	A& operator++()
	{
		_a1 += 100;
 
		return *this;
	}
private:
	int _a1 = 1;
	int _a2 = 1;
};
int main()
{
 
	A* p1 = new A;
	free(p1);//自定义类型，析构函数中没有释放资源，也不会造成内存泄漏
 
	return 0;
}

#include"iostream"
using namespace std;
int main()
{
	
 
	int* p1 = new int[10];
	delete p1;//不报错
 
 
	return 0;
}

class A
{
public:
	A(int a1 = 0, int a2 = 0)
		:_a1(a1)
		, _a2(a2)
	{
		cout << "A(int a1 = 0, int a2 = 0)" << endl;
	}
 
	A(const A& aa)
		:_a1(aa._a1)
	{
		cout << "A(const A& aa)" << endl;
	}
 
	A& operator=(const A& aa)
	{
		cout << "A& operator=(const A& aa)" << endl;
		if (this != &aa)
		{
			_a1 = aa._a1;
		}
		return *this;
	}
 
	~A()
	{
		//delete _ptr;
		cout << "~A()" << endl;
	}
 
	void Print()
	{
		cout << "A::Print->" << _a1 << endl;
	}
 
	A& operator++()
	{
		_a1 += 100;
 
		return *this;
	}
private:
	int _a1 = 1;
	int _a2 = 1;
};
 
class B
{
public:
	/*~B()
	{
		cout << "~B()" << endl;
	}*/
private:
	int _b1 = 2;
	int _b2 = 2;
};
 
#include"iostream"
using namespace std;
int main()
{
	
	A* p1 = new A[10];
	delete p1;//由于A类有析构函数，所以编译器会开四个字节存放要析构的个数，但是仅释放80个字节的空间，故由于不能从中间释放，所以系统崩溃
 
	B* p2 = new B[10];
	delete p2;//由于B类没有析构函数，不会再开头开4个字节的空间，故从头释放，不会崩溃
	return 0;
}

四.malloc/free和new/delete的区别

五.定位new表达式(placement-new)(构造函数)

class A
{
public:
	A(int a1 = 0, int a2 = 0)
		:_a1(a1)
		, _a2(a2)
	{
		cout << "A(int a1 = 0, int a2 = 0)" << endl;
	}
 
	A(const A& aa)
		:_a1(aa._a1)
	{
		cout << "A(const A& aa)" << endl;
	}
 
	A& operator=(const A& aa)
	{
		cout << "A& operator=(const A& aa)" << endl;
		if (this != &aa)
		{
			_a1 = aa._a1;
		}
		return *this;
	}
 
	~A()
	{
		//delete _ptr;
		cout << "~A()" << endl;
	}
 
	void Print()
	{
		cout << "A::Print->" << _a1 << endl;
	}
 
	A& operator++()
	{
		_a1 += 100;
 
		return *this;
	}
private:
	int _a1 = 1;
	int _a2 = 1;
};
 
#include"iostream"
using namespace std;
int main()
{
	A* p1 = new A(1);
	delete p1;
 
	A* p2 = (A*)operator new(sizeof(A));
	new(p2)A(1);
	p2->~A();
	operator delete(p2);
 
 
	return 0;
}

内存池(池化技术--》提高性能) 高频申请释放内存块(仅申请了空间，要调用operator new初始化)