C++裸指针和智能指针的效率对比

#include <iostream>
#include <memory>
#include <Windows.h>
#include <queue>
#include <Psapi.h>
using namespace std;

static size_t	s_my_int_count = 0;
const  int		MAX_LOOP_ = 3000000;

const int      NORMAL_FLAG = 0x12ff0101;
const int	   MY_INT_FLAG = 0x12ff0102;

void* operator new(std::size_t size)throw(std::bad_alloc)//重写new操作符为的是统计我们关心的内存分配
{
	int addLen = sizeof(size_t);
	void * p = std::malloc(addLen + 4 + size) ;

	if (!p)
		throw std::bad_alloc() ;

	memcpy(p, &size, addLen);//标志实际长度
	memcpy((char*)p + addLen, &NORMAL_FLAG, 4);//标志类型，普通---0x12ff0101, 我自己的int---0x12ff0102, 我自己的char[]---0x12ff0103
	return ((char*)p + addLen + 4);
}

void* operator new(std::size_t size, int flag)throw(std::bad_alloc)// 对应于调用 “new(MY_INT_FLAG) int” 这样所有我们关心的内存多可以被监视
{
	int addLen = sizeof(size_t);
	void * p = std::malloc(addLen + 4 + size) ;

	if (!p)
		throw std::bad_alloc() ;

	if (flag == MY_INT_FLAG){
		s_my_int_count ++;//统计关心的内存申请次数
	}

	memcpy(p, &size, addLen);//标志实际长度
	memcpy((char*)p + addLen, &flag, 4);//放置标志位，标志类型，普通---0x12ff0101, 我自己的int---0x12ff0102, 我自己的char[]---0x12ff0103
	return ((char*)p + addLen + 4);
}

void operator delete(void * q) throw()
{
	void* p;
	int addLen = sizeof(size_t);
	p = (char*)q - addLen - 4;//还原原来的指针位置，p是真正的系统malloc出来的指针
	int flag;
	memcpy(&flag, (char*)p + addLen, 4);//得到标志位
	
	if (flag == MY_INT_FLAG){//统计关心的内存释放次数
		s_my_int_count --;
	}

	if (p)
		std::free(p) ;
}

void main(){
	queue<int*>  intQueue;
	int count = 0;

	count = 0;

	cout << "before push " << s_my_int_count << " int allocated"<< endl;
	LONGLONG start = GetTickCount();
	for (int i = 0; i < MAX_LOOP_; i ++)
	{
		int* p = new(MY_INT_FLAG) int;
		intQueue.push(p);		
	}
	cout << "after push " << s_my_int_count << " int allocated"<< endl;
	while (!intQueue.empty()){
		int* p = intQueue.front();
		intQueue.pop();
		delete p;//注意需要手动释放
		count ++;
	}
	cout << "after pop " << s_my_int_count << " int allocated"<< endl;
	cout << "===================raw int ptr for " << count << "\t" << GetTickCount() - start << endl;


	unique_ptr<int> q(new int);
	unique_ptr<int> r = move(q);// 编译正确，r（q） 和 r = q则编译失败，因为unique_ptr已经不允许使用“拷贝构造函数”

	queue<unique_ptr<int>> intUniQueue;//因为unique_ptr没有“拷贝构造函数”  copy-constructor
	//所以push（）的参数不能是“左值”，左值会调用“拷贝构造函数”
	//只能是“右值”,右值则会调用“移动构造函数” move-constructor，  
	//std::move()函数可以强制将左值转化成为右值

	count = 0;
	start = GetTickCount();	
	cout << "before push " << s_my_int_count << " int allocated"<< endl;
	for (int i = 0; i < MAX_LOOP_; i ++)
	{
		unique_ptr<int> p(new(MY_INT_FLAG) int);
		intUniQueue.push(std::move(p));//因为p不是“右值”，所以我们需要“显式”的调用move将p强制转为右值。
	}
	cout << "after push " << s_my_int_count << " int allocated"<< endl;
	while (!intUniQueue.empty()){
		unique_ptr<int> p = std::move(intUniQueue.front());//queue.front() 是一个左值引用，即queue.front()=2 合法。
		intUniQueue.pop();
		count ++;
	}
	cout << "after pop " << s_my_int_count << " int allocated"<< endl;
	cout << "===================int unique  ptr for " << count << "\t" << GetTickCount() - start << endl;

	queue<shared_ptr<int>> intSharedQueue;
	count = 0;
	start = GetTickCount();	
	cout << "before push " << s_my_int_count << " int allocated"<< endl;
	for (int i = 0; i < MAX_LOOP_; i ++)
	{
		shared_ptr<int> p(new(MY_INT_FLAG) int);
		intSharedQueue.push(p);
	}
	cout << "after push " << s_my_int_count << " int allocated"<< endl;
	while (!intSharedQueue.empty()){
		auto p = intSharedQueue.front();
		intSharedQueue.pop();		
		count ++;
	}
	cout << "after pop " << s_my_int_count << " int allocated"<< endl;
	cout << "===================int shared ptr for " << count << "\t" << GetTickCount() - start << endl;

}

/*
智能指针省去了我们释放指针的精力，但是也需要一定的开销。unique_ptr 的开销相对于shared_ptr要小很多。
如果一个资源每个时刻都只要有一个支配者，我们还是优先使用unique_ptr吧，效率会高很多。

before push 0 int allocated
after push 3000000 int allocated
after pop 0 int allocated
===================raw int ptr for 3000000      5375
before push 0 int allocated
after push 3000000 int allocated
after pop 0 int allocated
===================int unique  ptr for 3000000  7313
before push 0 int allocated
after push 3000000 int allocated
after pop 0 int allocated
===================int shared ptr for 3000000   11171
请按任意键继续. . .
*/