[英]What's the difference between std::ranges::swap() and std::swap()?
[英]Time difference between swap and pop for for std::queue remove all of element
我正在尝试清除std::queue
以便已经对此进行了一些摆弄。 如何有效清除std :: queue?
我试图为此编写一个简单的代码。 我有一个关于“交换”和“流行”方法之间的时差的问题。
Test1和Test2是相同的总时间。 但是,方法内部的结果不同。
案例测试1:队列弹出
Wed Jul 22 11:33:33 2015 : 10000000 start queue Wed Jul 22 11:33:38 2015 : 10000000 queue push complete diff : 5592 milliseconds(msec) Wed Jul 22 11:33:38 2015 : 10000000 clear queue Wed Jul 22 11:33:42 2015 : 10000000 queue clear complete diff : 3561 milliseconds(msec) diff between after TEST1 : 135644 milliseconds(msec)
案例Test2:队列交换
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)
有什么理由起作用吗?
环境:Windows7(x64),MSVC2013
程式码片段:
#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;
}
}
看起来像std::queue
时,被替换为while()/ pop()。 如果基础结构是一个链表,则尤其如此,因为必须在每个元素上进行迭代以释放内存。
交换似乎与while / pop循环发生相同的原因是因为您已将数据从空队列“移”到队列对象中(反之亦然)-队列对象现在为空,但是您所要做的只是完成后,将数据移到临时队列对象中,一旦Clear函数返回,该对象将立即释放,这是由于对empty
的自动作用域导致调用了其描述符。
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