{"id":6015,"date":"2020-10-18T15:59:49","date_gmt":"2020-10-18T15:59:49","guid":{"rendered":"https:\/\/www.modernescpp.com\/index.php\/calendar-and-time-zone-in-c-20-working-with-calendar-dates\/"},"modified":"2023-06-26T09:37:36","modified_gmt":"2023-06-26T09:37:36","slug":"calendar-and-time-zone-in-c-20-working-with-calendar-dates","status":"publish","type":"post","link":"https:\/\/www.modernescpp.com\/index.php\/calendar-and-time-zone-in-c-20-working-with-calendar-dates\/","title":{"rendered":"Calendar and Time-Zones in C++20: Handling Calendar Dates"},"content":{"rendered":"

In my last post, “Calendar and Time Zone in C++20: Calendar Dates”, I presented the new calendar-related data types. Today, I go one step further and interact with them.<\/p>\n

<\/p>\n

 \"TimelineCpp20CoreLanguage\"<\/p>\n

Assume you have a calendar date, such as year(2100)\/2\/29. <\/code>Your first question may be: Is this date valid?<\/p>\n

Check if a Date is Valid<\/h2>\n

The various calendar types in C++20 have a function ok<\/code>. This function returns true<\/code> if the date is valid.<\/p>\n

 <\/p>\n

<\/p>\n

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\/\/  leapYear.cpp<\/span>\r\n\r\n#include <iostream><\/span>\r\n#include \"date.h\"<\/span>\r\n \r\nint<\/span> main<\/span>() {\r\n\r\n    std::<\/span>cout <<<\/span> std::<\/span>boolalpha <<<\/span> std::<\/span>endl;\r\n    \r\n    using<\/span> namespace<\/span> date; \r\n\r\n    std::<\/span>cout <<<\/span> \"Valid days\"<\/span> <<<\/span> std::<\/span>endl;         \/\/ (1)<\/span>       \r\n    day day31(31<\/span>);\r\n    day day32 =<\/span> day31 +<\/span> days(1<\/span>);\r\n    std::<\/span>cout <<<\/span> \"  day31: \"<\/span> <<<\/span> day31 <<<\/span> \"; \"<\/span>;\r\n    std::<\/span>cout <<<\/span> \"                   day31.ok(): \"<\/span>  <<<\/span> day31.ok() <<<\/span> std::<\/span>endl;\r\n    std::<\/span>cout <<<\/span> \"  day32: \"<\/span> <<<\/span> day32 <<<\/span> \"; \"<\/span>;\r\n    std::<\/span>cout <<<\/span> \"day32.ok(): \"<\/span>  <<<\/span> day32.ok() <<<\/span> std::<\/span>endl;\r\n   \r\n\r\n    std::<\/span>cout <<<\/span> std::<\/span>endl;\r\n\r\n    std::<\/span>cout <<<\/span> \"Valid months\"<\/span> <<<\/span> std::<\/span>endl;       \/\/ (2)<\/span> \r\n    month month1(1<\/span>);\r\n    month month0(0<\/span>);\r\n    std::<\/span>cout <<<\/span> \"  month1: \"<\/span> <<<\/span> month1 <<<\/span> \"; \"<\/span>;\r\n    std::<\/span>cout <<<\/span> \"                   month1.ok(): \"<\/span>  <<<\/span> month1.ok() <<<\/span> std::<\/span>endl;\r\n    std::<\/span>cout <<<\/span> \"  month0: \"<\/span> <<<\/span> month0 <<<\/span> \"; \"<\/span>;\r\n    std::<\/span>cout <<<\/span> \"month0.ok(): \"<\/span>  <<<\/span> month0.ok() <<<\/span> std::<\/span>endl;\r\n\r\n    std::<\/span>cout <<<\/span> std::<\/span>endl;\r\n\r\n    std::<\/span>cout <<<\/span> \"Valid years\"<\/span> <<<\/span> std::<\/span>endl;       \/\/ (3)<\/span> \r\n    year year2020(2020<\/span>);\r\n    year year32768(-<\/span>32768<\/span>);\r\n    std::<\/span>cout <<<\/span> \"  year2020: \"<\/span> <<<\/span> year2020 <<<\/span> \"; \"<\/span>;\r\n    std::<\/span>cout <<<\/span> \"                       year2020.ok(): \"<\/span>  <<<\/span> year2020.ok() <<<\/span> std::<\/span>endl;\r\n    std::<\/span>cout <<<\/span> \"  year32768: \"<\/span> <<<\/span> year32768 <<<\/span> \"; \"<\/span>;\r\n    std::<\/span>cout <<<\/span> \"year32768.ok(): \"<\/span>  <<<\/span> year32768.ok() <<<\/span> std::<\/span>endl;\r\n\r\n    std::<\/span>cout <<<\/span> std::<\/span>endl;\r\n\r\n    std::<\/span>cout <<<\/span> \"Leap Years\"<\/span>  <<<\/span> std::<\/span>endl;       \/\/ (4)<\/span> \r\n\r\n    constexpr auto<\/span> leapYear2016{year(2016<\/span>)\/<\/span>2<\/span>\/<\/span>29<\/span>};\r\n    constexpr auto<\/span> leapYear2020{year(2020<\/span>)\/<\/span>2<\/span>\/<\/span>29<\/span>};\r\n    constexpr auto<\/span> leapYear2024{year(2024<\/span>)\/<\/span>2<\/span>\/<\/span>29<\/span>};\r\n\r\n    std::<\/span>cout <<<\/span> \"  leapYear2016.ok(): \"<\/span> <<<\/span> leapYear2016.ok() <<<\/span> std::<\/span>endl;\r\n    std::<\/span>cout <<<\/span> \"  leapYear2020.ok(): \"<\/span> <<<\/span> leapYear2020.ok() <<<\/span> std::<\/span>endl;\r\n    std::<\/span>cout <<<\/span> \"  leapYear2024.ok(): \"<\/span> <<<\/span> leapYear2024.ok() <<<\/span> std::<\/span>endl;\r\n\r\n    std::<\/span>cout <<<\/span> std::<\/span>endl;\r\n\r\n     std::<\/span>cout <<<\/span> \"No Leap Years\"<\/span>  <<<\/span> std::<\/span>endl;   \/\/ (5)<\/span> \r\n\r\n    constexpr auto<\/span> leapYear2100{year(2100<\/span>)\/<\/span>2<\/span>\/<\/span>29<\/span>};\r\n    constexpr auto<\/span> leapYear2200{year(2200<\/span>)\/<\/span>2<\/span>\/<\/span>29<\/span>};\r\n    constexpr auto<\/span> leapYear2300{year(2300<\/span>)\/<\/span>2<\/span>\/<\/span>29<\/span>};\r\n\r\n    std::<\/span>cout <<<\/span> \"  leapYear2100.ok(): \"<\/span> <<<\/span> leapYear2100.ok() <<<\/span> std::<\/span>endl;\r\n    std::<\/span>cout <<<\/span> \"  leapYear2200.ok(): \"<\/span> <<<\/span> leapYear2200.ok() <<<\/span> std::<\/span>endl;\r\n    std::<\/span>cout <<<\/span> \"  leapYear2300.ok(): \"<\/span> <<<\/span> leapYear2300.ok() <<<\/span> std::<\/span>endl;\r\n\r\n    std::<\/span>cout <<<\/span> std::<\/span>endl;\r\n\r\n    std::<\/span>cout <<<\/span> \"Leap Years\"<\/span>  <<<\/span> std::<\/span>endl;      \/\/ (6)<\/span> \r\n\r\n    constexpr auto<\/span> leapYear2000{year(2000<\/span>)\/<\/span>2<\/span>\/<\/span>29<\/span>};\r\n    constexpr auto<\/span> leapYear2400{year(2400<\/span>)\/<\/span>2<\/span>\/<\/span>29<\/span>};\r\n    constexpr auto<\/span> leapYear2800{year(2800<\/span>)\/<\/span>2<\/span>\/<\/span>29<\/span>};\r\n\r\n    std::<\/span>cout <<<\/span> \"  leapYear2000.ok(): \"<\/span> <<<\/span> leapYear2000.ok() <<<\/span> std::<\/span>endl;\r\n    std::<\/span>cout <<<\/span> \"  leapYear2400.ok(): \"<\/span> <<<\/span> leapYear2400.ok() <<<\/span> std::<\/span>endl;\r\n    std::<\/span>cout <<<\/span> \"  leapYear2800.ok(): \"<\/span> <<<\/span> leapYear2800.ok() <<<\/span> std::<\/span>endl;\r\n\r\n    std::<\/span>cout <<<\/span> std::<\/span>endl;\r\n\r\n}\r\n<\/pre>\n<\/div>\n
 <\/p>\n
I checked in the program if a given day (line 1), a given month (line 2), or a given year (line 3) is valid. The range of a day is [1, 31], of a month [1, 12], and of a year [ -32767, 32767]. Consequently, the ok<\/code>-call on the corresponding values returns false<\/code>. Two facts are interesting when I output the various values. First, if the value is not valid, the output displays: \"is not a valid day<\/code>“; \"is not a valid month<\/code>“; \"is not a valid year<\/code>“. Second, month values are displayed in string representation.<\/p>\n
\"leapYears\"<\/p>\n
You can apply the ok<\/code>-call on a calendar date. Now it’s pretty easy to check if a specific calendar date is a leap day and, therefore, the corresponding year a leap year. In the worldwide used Gregorian calendar<\/a>, the following rules apply:<\/p>\n
Each year that is exactly divisible by 4<\/strong> is a leap yea<\/strong>r.<\/p>\n