Boost.Date_Time

Boost.Date_Time provides date and time types for C++: calendar dates (gregorian::date), time-of-day values (posix_time::ptime, posix_time::time_duration), time zones, periods, and date arithmetic. It was the first serious date/time library for C++ and influenced both std::chrono (C++11, for durations and clocks) and the calendar additions in C++20.

The problem it solves

<ctime> gives you time_t and struct tm — a raw integer and a broken-down struct with no type safety, no date arithmetic, no time zones, and one-second resolution. Boost.Date_Time replaces this with value types where adding "3 months" to a date is a single function call and the compiler rejects nonsensical operations.

Gregorian dates

dates.cpp
#include <boost/date_time/gregorian/gregorian.hpp>
#include <iostream>

namespace greg = boost::gregorian;

int main() {
    greg::date today  = greg::day_clock::local_day();
    greg::date launch(2026, greg::Apr, 7);

    std::cout << "today:  " << today << "\n";
    std::cout << "launch: " << launch << "\n";

    greg::date_duration diff = today - launch;
    std::cout << "days since launch: " << diff.days() << "\n";

    greg::date next_month = launch + greg::months(1);
    std::cout << "one month later: " << next_month << "\n";
}

Date arithmetic

Operation	Code	Result type
Difference	`d2 - d1`	`date_duration` (days)
Add days	`d + days(7)`	`date`
Add months	`d + months(3)`	`date` (end-of-month clamped)
Add years	`d + years(1)`	`date`
Day of week	`d.day_of_week()`	`greg_weekday` (0 = Sunday)

End-of-month clamping

Adding one month to January 31 gives February 28 (or 29 in a leap year) — it clamps to the last valid day rather than overflowing.

Posix time — date + time of day

ptime combines a date with a time_duration to represent a point in time with microsecond resolution.

ptime.cpp
#include <boost/date_time/posix_time/posix_time.hpp>
#include <iostream>

namespace pt = boost::posix_time;
namespace greg = boost::gregorian;

int main() {
    pt::ptime now = pt::second_clock::local_time();
    std::cout << "now: " << now << "\n";

    pt::ptime meeting(greg::date(2026, 4, 10),
                      pt::hours(14) + pt::minutes(30));
    std::cout << "meeting: " << meeting << "\n";

    pt::time_duration until = meeting - now;
    std::cout << "hours until meeting: " << until.hours() << "\n";
}

Time periods

A time_period represents a half-open interval [begin, end). Useful for scheduling, overlap detection, and containment queries.

periods.cpp
#include <boost/date_time/posix_time/posix_time.hpp>

namespace pt = boost::posix_time;
namespace greg = boost::gregorian;

int main() {
    pt::ptime start(greg::date(2026, 4, 7), pt::hours(9));
    pt::ptime end(greg::date(2026, 4, 7), pt::hours(17));
    pt::time_period workday(start, end);

    pt::ptime lunch(greg::date(2026, 4, 7), pt::hours(12));
    bool during_work = workday.contains(lunch); // true
    (void)during_work;
}

Parsing and formatting

format.cpp
#include <boost/date_time/posix_time/posix_time.hpp>
#include <iostream>

namespace pt = boost::posix_time;
namespace greg = boost::gregorian;

int main() {
    // Parsing
    greg::date d = greg::from_string("2026-04-07");
    pt::ptime t = pt::time_from_string("2026-04-07 14:30:00");

    // ISO format
    std::cout << greg::to_iso_extended_string(d) << "\n";   // 2026-04-07
    std::cout << pt::to_iso_string(t) << "\n";               // 20260407T143000

    // Simple string
    std::cout << pt::to_simple_string(t) << "\n";            // 2026-Apr-07 14:30:00
}

Boost.Date_Time versus `std::chrono` and C++20 calendar

Feature	Boost.Date_Time	`std::chrono` (C++11)	C++20 calendar
Duration types	`time_duration`	`duration<>`	`duration<>`
Calendar dates	`gregorian::date`	No	`year_month_day`
Date arithmetic	`+ months(3)`	No	`+ months{3}`
Time zones	`local_date_time`	No	`zoned_time`
Parsing/formatting	Built-in	`from_stream` (C++20)	`from_stream`
Resolution	Microseconds	Arbitrary	Arbitrary

When to use which

std::chrono is the go-to for durations, clocks, and benchmarking. For calendar operations on C++17 or earlier, Boost.Date_Time fills the gap that std::chrono left until C++20. On C++20, prefer std::chrono's calendar types unless you need Date_Time's time-zone database or are already using Boost.

Linking

Date_Time is partially compiled:

g++ -std=c++17 dates.cpp -lboost_date_time

Gregorian dates​

Date arithmetic​

Posix time — date + time of day​

Time periods​

Parsing and formatting​

Boost.Date_Time versus std::chrono and C++20 calendar​

Linking​

See also​