C++ std::queue删除所有元素的交换和pop之间的时间差
我正试图清除C++ std::queue删除所有元素的交换和pop之间的时间差,c++,queue,std,swap,C++,Queue,Std,Swap,我正试图清除std::queue,这样就已经有一些人在摆姿势了 我试着为此编写一个简单的代码。我有一个关于“交换”和“弹出”方法之间时间差的问题 Test1和Test2是相同的总时间。然而,方法内部的结果是不同的 案例Test1:队列pop 案例测试2:队列交换 这有什么原因吗 环境: Windows7(x64), MSVC2013 代码段: #include <iostream> #include <exception> #include <chrono>
std::queue
,这样就已经有一些人在摆姿势了
我试着为此编写一个简单的代码。我有一个关于“交换”和“弹出”方法之间时间差的问题
Test1和Test2是相同的总时间。然而,方法内部的结果是不同的
案例Test1:队列pop
案例测试2:队列交换
这有什么原因吗
环境:
Windows7(x64),
MSVC2013
代码段:
#include <iostream>
#include <exception>
#include <chrono>
#include <queue>
#include <vector>
#include <ctime>
#include <string>
using namespace std;
std::string asString(const std::chrono::system_clock::time_point& tp)
{
std::time_t t = std::chrono::system_clock::to_time_t(tp);
std::string ts = std::ctime(&t);
ts.resize(ts.size() - 1);
return ts;
}
template<class T>
void clear(std::queue<T> &q)
{
std::queue<T> empty;
std::swap(q, empty);
}
void Test1(int itemCount, int mode)
{
queue<int> q;
std::chrono::system_clock::time_point tp_push = std::chrono::system_clock::now();
std::cout << asString(tp_push) << " : " << itemCount << " start queue : mode - " << mode << endl;
for (int i = 0; i < itemCount; i++)
{
q.push(i);
}
std::cout << asString(std::chrono::system_clock::now()) << " : " << itemCount << " queue push complete " << endl;
auto diff_push = std::chrono::system_clock::now() - tp_push;
std::cout << " diff : "
<< chrono::duration_cast<chrono::milliseconds>(diff_push).count()
<< " milliseconds(msec) " << endl;
std::chrono::system_clock::time_point tp_clear = std::chrono::system_clock::now();
std::cout << asString(tp_clear) << " : " << itemCount << " clear queue " << endl;
if (mode)
{
clear(q);
}
else
{
while (!q.empty())
{
q.pop();
}
}
std::cout << asString(std::chrono::system_clock::now()) << " : " << itemCount << " queue clear complete " << endl;
auto diff_clear = std::chrono::system_clock::now() - tp_clear;
std::cout << " diff : "
<< chrono::duration_cast<chrono::milliseconds>(diff_clear).count()
<< " milliseconds(msec) " << endl;
}
int main()
{
try
{
int itemCount = 10000000;
std::chrono::system_clock::time_point tp_test1 = std::chrono::system_clock::now();
Test1(itemCount, 0);
auto diff_test1 = std::chrono::system_clock::now() - tp_test1;
std::cout << " diff between after TEST1 : "
<< chrono::duration_cast<chrono::milliseconds>(diff_test1).count()
<< " milliseconds(msec) " << endl;
std::chrono::system_clock::time_point tp_test2 = std::chrono::system_clock::now();
Test1(itemCount, 1);
auto diff_test2 = std::chrono::system_clock::now() - tp_test2;
std::cout << " diff after TEST2 : "
<< chrono::duration_cast<chrono::milliseconds>(diff_test2).count()
<< " milliseconds(msec) " << endl;
}
catch (const exception& e)
{
cerr << "EXCEPTION : " << e.what() << endl;
}
}
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使用名称空间std;
标准::字符串关联(常数标准::时钟::系统时钟::时间点和tp)
{
std::time\u t=std::chrono::system\u clock::to\u time\u t(tp);
std::string ts=std::ctime(&t);
ts.resize(ts.size()-1);
返回ts;
}
模板
无效清除(标准::队列和q)
{
std::队列为空;
std::交换(q,空);
}
void Test1(int itemCount,int模式)
{
队列q;
std::chrono::system_clock::time_point tp_push=std::chrono::system_clock::now();
std::cout当交换时,它看起来像是std::queue
,相当于while()/pop()。如果底层结构是链表,这一点尤其正确,因为它必须在每个元素上迭代以释放内存
swap之所以看起来与while/pop循环做相同的事情,是因为您已将数据从空队列“移动”到队列对象中(反之亦然)-您的队列对象现在为空,但您所做的只是将数据移动到一个临时队列对象中,该对象在Clear函数返回后立即被释放,这是因为empty
的自动作用域导致调用其descructor
Wed Jul 22 11:37:45 2015 : 10000000 start queue
Wed Jul 22 11:37:51 2015 : 10000000 queue push complete
diff : 5875 milliseconds(msec)
Wed Jul 22 11:37:51 2015 : 10000000 clear queue
Wed Jul 22 11:40:00 2015 : 10000000 queue clear complete
diff : 129130 milliseconds(msec)
diff between after TEST2 : 135006 milliseconds(msec)
#include <iostream>
#include <exception>
#include <chrono>
#include <queue>
#include <vector>
#include <ctime>
#include <string>
using namespace std;
std::string asString(const std::chrono::system_clock::time_point& tp)
{
std::time_t t = std::chrono::system_clock::to_time_t(tp);
std::string ts = std::ctime(&t);
ts.resize(ts.size() - 1);
return ts;
}
template<class T>
void clear(std::queue<T> &q)
{
std::queue<T> empty;
std::swap(q, empty);
}
void Test1(int itemCount, int mode)
{
queue<int> q;
std::chrono::system_clock::time_point tp_push = std::chrono::system_clock::now();
std::cout << asString(tp_push) << " : " << itemCount << " start queue : mode - " << mode << endl;
for (int i = 0; i < itemCount; i++)
{
q.push(i);
}
std::cout << asString(std::chrono::system_clock::now()) << " : " << itemCount << " queue push complete " << endl;
auto diff_push = std::chrono::system_clock::now() - tp_push;
std::cout << " diff : "
<< chrono::duration_cast<chrono::milliseconds>(diff_push).count()
<< " milliseconds(msec) " << endl;
std::chrono::system_clock::time_point tp_clear = std::chrono::system_clock::now();
std::cout << asString(tp_clear) << " : " << itemCount << " clear queue " << endl;
if (mode)
{
clear(q);
}
else
{
while (!q.empty())
{
q.pop();
}
}
std::cout << asString(std::chrono::system_clock::now()) << " : " << itemCount << " queue clear complete " << endl;
auto diff_clear = std::chrono::system_clock::now() - tp_clear;
std::cout << " diff : "
<< chrono::duration_cast<chrono::milliseconds>(diff_clear).count()
<< " milliseconds(msec) " << endl;
}
int main()
{
try
{
int itemCount = 10000000;
std::chrono::system_clock::time_point tp_test1 = std::chrono::system_clock::now();
Test1(itemCount, 0);
auto diff_test1 = std::chrono::system_clock::now() - tp_test1;
std::cout << " diff between after TEST1 : "
<< chrono::duration_cast<chrono::milliseconds>(diff_test1).count()
<< " milliseconds(msec) " << endl;
std::chrono::system_clock::time_point tp_test2 = std::chrono::system_clock::now();
Test1(itemCount, 1);
auto diff_test2 = std::chrono::system_clock::now() - tp_test2;
std::cout << " diff after TEST2 : "
<< chrono::duration_cast<chrono::milliseconds>(diff_test2).count()
<< " milliseconds(msec) " << endl;
}
catch (const exception& e)
{
cerr << "EXCEPTION : " << e.what() << endl;
}
}