CODEWITHSUNDEEP
c++time
Michał Dadej
Michał Dadej

Reputation: 93

C++ How to convert date from input (string year, string month, string day) to time_point

My teacher said that i have to convert the file with lines like that:

Jan Kowalski 1997 4 3

to class person with pools like:

string name, surname;
std::chrono::system_clock::time_point dateofbirth;

How can i create time point from 3 integers? I suppose it is not the easiest way to store that kind of data.

"A reference to a specific point in time, like one's birthday, today's dawn, or when the next train passes. In this library, objects of the time_point class template express this by using a duration relative to an epoch (which is a fixed point in time common to all time_point objects using the same clock)."

But how do i make duration from those data?

I suppose i should start with something like:

using std::chrono::system_clock;
system_clock::time_point today = system_clock::now();
std::chrono::duration<int, std::ratio<60 * 60 * 24> > one_day;

Upvotes: 4

Views: 3433

Answers (3)

Build Succeeded
Build Succeeded

Reputation: 1150

// create tm with 1/1/2000:

std::tm timeinfo = std::tm();

timeinfo.tm_year = 100; // year: 2000

timeinfo.tm_mon = 0; // month: january

timeinfo.tm_mday = 1; // day: 1st

std::time_t tt = std::mktime (&timeinfo);

system_clock::time_point tp = system_clock::from_time_t (tt);

Example is here to convert the std::tm to time_point: http://www.cplusplus.com/reference/chrono/system_clock/from_time_t/

Upvotes: 1

Howard Hinnant
Howard Hinnant

Reputation: 218750

Here are several low-level date algorithms which can be used to convert three integers into a std::chrono::system_clock::time_point:

chrono-Compatible Low-Level Date Algorithms

You can view this paper as a cookbook for how to write the algorithms portion of a date class.

Here is an example date class based on these algorithms. It contains a type-alias called days that is quite similar to your one_day.

date

Here is a time zone library built on top of date that includes a parse function that can be used to parse dates (and times) out of files:

Time Zone Database Parser

As this is homework, you may just want to stick with the underlying algorithms paper.

Upvotes: 3

Moreira
Moreira

Reputation: 586

You can start by storing the birth date in std::tm (http://en.cppreference.com/w/cpp/chrono/c/tm), a structure that holds a date and time broken down into its components. For example:

std::tm tm;
tm.tm_mday = 3;
tm.tm_mon = 4;
tm.tm_year = 1977;

This std::tm structure can be converted to std::time_t (http://en.cppreference.com/w/c/chrono/time_t), which holds the number of seconds since epoch.

std::time_t tt = timegm(&tm);

Which in turn can be used to create the std::chrono::system_clock::time_point you are looking for:

std::chrono::system_clock::time_point dateofbirth = std::chrono::system_clock::from_time_t(tt);

Upvotes: 5

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