标签：www 方式 tick class solution time_t nano minutes stars
所谓的详解只不过是参考www.cplusplus.com的说明整理了一下，因为没发现别人有详细讲解。
chrono是一个time library, 源于boost，现在已经是C++标准。话说今年似乎又要出新标准了，好期待啊！
要使用chrono库，需要#include<chrono>，其所有实现均在std::chrono namespace下。注意标准库里面的每个命名空间代表了一个独立的概念。所以下文中的概念均以命名空间的名字表示！ chrono是一个模版库，使用简单，功能强大，只需要理解三个概念：duration、time_point、clock
1 template <class Rep, class Period = ratio<1> > class duration;
1 template <intmax_t N, intmax_t D = 1> class ratio;
1 template <class ToDuration, class Rep, class Period> 2 constexpr ToDuration duration_cast (const duration<Rep,Period>& dtn);
1 // duration constructor
2 #include <iostream>
3 #include <ratio>
4 #include <chrono>
5
6 int main ()
7 {
8 typedef std::chrono::duration<int> seconds_type;
9 typedef std::chrono::duration<int,std::milli> milliseconds_type;
10 typedef std::chrono::duration<int,std::ratio<60*60>> hours_type;
11
12 hours_type h_oneday (24); // 24h
13 seconds_type s_oneday (60*60*24); // 86400s
14 milliseconds_type ms_oneday (s_oneday); // 86400000ms
15
16 seconds_type s_onehour (60*60); // 3600s
17 //hours_type h_onehour (s_onehour); // NOT VALID (type truncates), use:
18 hours_type h_onehour (std::chrono::duration_cast<hours_type>(s_onehour));
19 milliseconds_type ms_onehour (s_onehour); // 3600000ms (ok, no type truncation)
20
21 std::cout << ms_onehour.count() << "ms in 1h" << std::endl;
22
23 return 0;
24 }
25
26 duration还有一个成员函数count()返回Rep类型的Period数量，看代码：
27
28 // duration::count
29 #include <iostream> // std::cout
30 #include <chrono> // std::chrono::seconds, std::chrono::milliseconds
31 // std::chrono::duration_cast
32
33 int main ()
34 {
35 using namespace std::chrono;
36 // std::chrono::milliseconds is an instatiation of std::chrono::duration:
37 milliseconds foo (1000); // 1 second
38 foo*=60;
39
40 std::cout << "duration (in periods): ";
41 std::cout << foo.count() << " milliseconds.\n";
42
43 std::cout << "duration (in seconds): ";
44 std::cout << foo.count() * milliseconds::period::num / milliseconds::period::den;
45 std::cout << " seconds.\n";
46
47 return 0;
48 }
1 template <class Clock, class Duration = typename Clock::duration> class time_point;
1 // time_point constructors
2 #include <iostream>
3 #include <chrono>
4 #include <ctime>
5
6 int main ()
7 {
8 using namespace std::chrono;
9
10 system_clock::time_point tp_epoch; // epoch value
11
12 time_point <system_clock,duration<int>> tp_seconds (duration<int>(1));
13
14 system_clock::time_point tp (tp_seconds);
15
16 std::cout << "1 second since system_clock epoch = ";
17 std::cout << tp.time_since_epoch().count();
18 std::cout << " system_clock periods." << std::endl;
19
20 // display time_point:
21 std::time_t tt = system_clock::to_time_t(tp);
22 std::cout << "time_point tp is: " << ctime(&tt);
23
24 return 0;
25 }
26
1 template <class ToDuration, class Clock, class Duration> 2 time_point<Clock,ToDuration> time_point_cast (const time_point<Clock,Duration>& tp);
1 / time_point_cast
2 #include <iostream>
3 #include <ratio>
4 #include <chrono>
5
6 int main ()
7 {
8 using namespace std::chrono;
9
10 typedef duration<int,std::ratio<60*60*24>> days_type;
11
12 time_point<system_clock,days_type> today = time_point_cast<days_type>(system_clock::now());
13
14 std::cout << today.time_since_epoch().count() << " days since epoch" << std::endl;
15
16 return 0;
17 }
1 // system_clock example
2 #include <iostream>
3 #include <ctime>
4 #include <ratio>
5 #include <chrono>
6
7 int main ()
8 {
9 using std::chrono::system_clock;
10
11 std::chrono::duration<int,std::ratio<60*60*24> > one_day (1);
12
13 system_clock::time_point today = system_clock::now();
14 system_clock::time_point tomorrow = today + one_day;
15
16 std::time_t tt;
17
18 tt = system_clock::to_time_t ( today );
19 std::cout << "today is: " << ctime(&tt);
20
21 tt = system_clock::to_time_t ( tomorrow );
22 std::cout << "tomorrow will be: " << ctime(&tt);
23
24 return 0;
25 }
26
1 // steady_clock example
2 #include <iostream>
3 #include <ctime>
4 #include <ratio>
5 #include <chrono>
6
7 int main ()
8 {
9 using namespace std::chrono;
10
11 steady_clock::time_point t1 = steady_clock::now();
12
13 std::cout << "printing out 1000 stars...\n";
14 for (int i=0; i<1000; ++i) std::cout << "*";
15 std::cout << std::endl;
16
17 steady_clock::time_point t2 = steady_clock::now();
18
19 duration<double> time_span = duration_cast<duration<double>>(t2 - t1);
20
21 std::cout << "It took me " << time_span.count() << " seconds.";
22 std::cout << std::endl;
23
24 return 0;
25 }
26
标签：www 方式 tick class solution time_t nano minutes stars
原文地址：http://www.cnblogs.com/alenoscar/p/7067129.html
