time since epoch

C++11 提供了新的获取系统时间的库函数，在获取时间的时候一般常用的是获取time since epoch，下面来看一下如何获取这个时间。

 

 1 #include <iostream>
 2 #include <chrono>
 3 #include <ctime>
 4 #include <sys/time.h>
 5 #include <cstdint>
 6 constexpr int microSecPerSec = 1000000;
 7  
 8 int main()
 9 {
10     std::chrono::time_point<std::chrono::system_clock> p1, p2, p3;
11     struct timeval tv;
12     int64_t mSecond;
13  
14     p2 = std::chrono::system_clock::now();
15     p3 = p2 - std::chrono::hours(24);
16     gettimeofday(&tv,NULL);
17     mSecond = tv.tv_sec ;
18  
19     std::time_t epoch_time = std::chrono::system_clock::to_time_t(p1); // seconds
20     std::cout << "epoch: " << std::ctime(&epoch_time);
21     std::time_t today_time = std::chrono::system_clock::to_time_t(p2);
22     std::cout << "today: " << std::ctime(&today_time);
23  
24     std::cout << "hours since epoch: "
25                 << std::chrono::duration_cast<std::chrono::hours>(   //hours
26                    p2.time_since_epoch()).count() 
27                 << std::endl;
28                 
29     std::cout << "yesterday, hours since epoch: "
30                 << std::chrono::duration_cast<std::chrono::hours>(
31                    p3.time_since_epoch()).count() 
32                 << std::endl;
33               
34     std::cout << "Microseconds since epoch: (chrono) : "   //microseconds
35                 << std::chrono::duration_cast<std::chrono::microseconds>(p2.time_since_epoch()).count() // p2 - p1 ==
36                 <<std::endl;
37                 
38     std::cout << "Microseconds since epoch: (gettimeofday) :" << mSecond * microSecPerSec + tv.tv_usec 
39                 <<std::endl;
40                 
41     return 0;
42 }

结果：

C:\Users\zhuyp\Desktop\tmp>cpp_time
epoch: Thu Jan 01 08:00:00 1970
today: Fri Jan 24 23:51:10 2014
hours since epoch: 386271
yesterday, hours since epoch: 386247
Microseconds since epoch: (chrono) : 1390578670080869
Microseconds since epoch: (gettimeofday) :1390578670080869