<\/p>\n
template<\/span><\r\n class<\/span> Clock<\/span>,\r\n class<\/span> Duration<\/span>= typename<\/span> Clock::duration\r\n>\r\nclass<\/span> time_point<\/span>;\r\n<\/pre>\n<\/div>\n <\/p>\n
There a four special time points depending on the clock.<\/p>\n
\n- epoch<\/strong>: The starting point of the clock.<\/li>\n
- now<\/strong>: The current time.<\/li>\n
- min<\/strong>: The minimum time point that the clock can display.<\/li>\n
- max<\/strong>: The maximum time point that the clock can display.<\/li>\n<\/ul>\n
The accuracy of the values depends on the used clock: std::system::system_clock, std::chrono::steady_clock<\/span>, or std::chrono::high_resolution_clock<\/span>.<\/p>\nC++ gives no guarantee about a clock’s accuracy, starting point, or valid time range. The starting point of std::chrono::system_clock is typically the 1.1.1970, the so-called UNIX-epoch<\/a>. It holds further that the std::chrono::high_resolution<\/span> clock has the highest accuracy.<\/p>\n<\/p>\nDisplaying a time duration as a date<\/h3>\n
If the time point uses internally std::chrono::system_clock<\/span>, you can convert the time point with the help of <\/span>std::chrono::system_clock::to_time_t <\/a>in an object of type std::time_t<\/a>. Thanks to further conversions with the functions std::gmtime<\/a> and std::asctime<\/a>, you have the time points as dates in textual representation available.<\/p>\n <\/p>\n
<\/p>\n
\n\n\n\n\n 1\r\n 2\r\n 3\r\n 4\r\n 5\r\n 6\r\n 7\r\n 8\r\n 9\r\n10\r\n11\r\n12\r\n13\r\n14\r\n15\r\n16\r\n17\r\n18\r\n19\r\n20\r\n21\r\n22\r\n23\r\n24\r\n25\r\n26\r\n27\r\n28\r\n29\r\n30\r\n31<\/pre>\n<\/td>\n\n\/\/ timepoint.cpp<\/span>\r\n\r\n#include <chrono><\/span>\r\n#include <ctime><\/span>\r\n#include <iomanip><\/span>\r\n#include <iostream><\/span>\r\n#include <string><\/span>\r\n\r\nint<\/span> main(){ \r\n \r\n std::cout << std::endl;\r\n \r\n std::chrono::time_point<std::chrono::system_clock> sysTimePoint;\r\n std::time_t<\/span> tp= std::chrono::system_clock::to_time_t<\/span>(sysTimePoint);\r\n std::string sTp= std::asctime(std::gmtime(&tp));\r\n std::cout << \"Epoch: \"<\/span> << sTp << std::endl;\r\n \r\n tp= std::chrono::system_clock::to_time_t<\/span>(sysTimePoint.min());\r\n sTp= std::asctime(std::gmtime(&tp));\r\n std::cout << \"Time min: \"<\/span> << sTp << std::endl;\r\n \r\n tp= std::chrono::system_clock::to_time_t<\/span>(sysTimePoint.max());\r\n sTp= std::asctime(std::gmtime(&tp));\r\n std::cout << \"Time max: \"<\/span> << sTp << std::endl;\r\n \r\n sysTimePoint= std::chrono::system_clock::now();\r\n tp= std::chrono::system_clock::to_time_t<\/span>(sysTimePoint);\r\n sTp= std::asctime(std::gmtime(&tp));\r\n std::cout << \"Time now: \"<\/span> << sTp << std::endl;\r\n \r\n}\r\n<\/pre>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n <\/p>\n
The output of the program shows the valid range of std::chrono::system_clock. std::chrono::system_clock<\/span> has the UNIX-epoch as starting point and can have time points between 1677 and 2262.<\/p>\n <\/p>\n
![\"timepoint\"](\"https:\/\/www.modernescpp.com\/wp-content\/uploads\/2016\/09\/timepoint.png\")
<\/p>\n
You can add time durations to time points to get new time points. Now I’m curious. What will happen if I’m out of the valid range of the time points?<\/p>\n
Beyond the boundaries of the valid time range<\/h3>\n
My experiment uses the current time and adds 1000 years or subtracts 1000 years from it. I ignore leap years and assume that the year has 365 days for simplicity.<\/p>\n
<\/p>\n
<\/p>\n
\n\n\n\n\n 1\r\n 2\r\n 3\r\n 4\r\n 5\r\n 6\r\n 7\r\n 8\r\n 9\r\n10\r\n11\r\n12\r\n13\r\n14\r\n15\r\n16\r\n17\r\n18\r\n19\r\n20\r\n21\r\n22\r\n23\r\n24\r\n25\r\n26\r\n27\r\n28\r\n29\r\n30<\/pre>\n<\/td>\n\n\/\/ timepointAddition.cpp\r\n\r\n#include <chrono><\/span>\r\n#include <ctime><\/span>\r\n#include <iomanip><\/span>\r\n#include <iostream><\/span>\r\n#include <string><\/span>\r\n\r\nusing namespace std::chrono;\r\n\r\nstd::string timePointAsString(const time_point<system_clock>& timePoint){\r\n std::time_t tp= system_clock::to_time_t(timePoint);\r\n return<\/span> std::asctime(std::gmtime(&tp));\r\n}\r\n\r\nint main(){ \r\n \r\n std::cout << std::endl;\r\n \r\n time_point<system_clock> nowTimePoint= system_clock::now();\r\n std::cout << \"Now: \"<\/span> << timePointAsString(nowTimePoint) << std::endl;\r\n \r\n auto thousandYears= hours(24*365*1000);\r\n time_point<system_clock> historyTimePoint= nowTimePoint - thousandYears;\r\n std::cout << \"Now - 1000 years: \"<\/span> << timePointAsString(historyTimePoint) << std::endl;\r\n \r\n time_point<system_clock> futureTimePoint= nowTimePoint + thousandYears;\r\n std::cout << \"Now + 1000 years: \"<\/span> << timePointAsString(futureTimePoint) << std::endl;\r\n \r\n}\r\n<\/pre>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n <\/p>\n
For the sake of readability, I introduced the namespace std::chrono. <\/span>The program’s output shows that an overflow of the time points in lines 24 and 27 causes wrong results. Subtracting 1000 years from the current time point gives a time point in the future; adding 1000 years to the current time point gives a time point in the past, respectively.<\/p>\n![\"timepointAddition\"](\"https:\/\/www.modernescpp.com\/wp-content\/uploads\/2016\/09\/timepointAddition.png\")
<\/p>\n
What’s next? <\/h2>\n