# Poco

# class DateTime

Library: Foundation
Package: DateTime
Header: Poco/DateTime.h

## Description

This class represents an instant in time, expressed in years, months, days, hours, minutes, seconds and milliseconds based on the Gregorian calendar. The class is mainly useful for conversions between UTC, Julian day and Gregorian calendar dates.

The date and time stored in a DateTime is always in UTC (Coordinated Universal Time) and thus independent of the timezone in effect on the system.

Conversion calculations are based on algorithms collected and described by Peter Baum at http://vsg.cape.com/~pbaum/date/date0.htm

Internally, this class stores a date/time in two forms (UTC and broken down) for performance reasons. Only use this class for conversions between date/time representations. Use the Timestamp class for everything else.

Notes:

- Zero is a valid year (in accordance with ISO 8601 and astronomical year numbering)
- Year zero (0) is a leap year
- Negative years (years preceding 1 BC) are not supported

For more information, please see:

- http://en.wikipedia.org/wiki/Gregorian_Calendar
- http://en.wikipedia.org/wiki/Julian_day
- http://en.wikipedia.org/wiki/UTC
- http://en.wikipedia.org/wiki/ISO_8601

## Member Summary

Member Functions: assign, computeDaytime, computeGregorian, day, dayOfWeek, dayOfYear, daysOfMonth, hour, hourAMPM, isAM, isLeapYear, isPM, isValid, julianDay, makeLocal, makeUTC, microsecond, millisecond, minute, month, operator !=, operator +, operator +=, operator -, operator -=, operator <, operator <=, operator =, operator ==, operator >, operator >=, second, swap, timestamp, toJulianDay, toUtcTime, utcTime, week, year

## Enumerations

### DaysOfWeek

Symbolic names for week day numbers (0 to 6).

SUNDAY = 0

MONDAY

TUESDAY

WEDNESDAY

THURSDAY

FRIDAY

SATURDAY

### Months

Symbolic names for month numbers (1 to 12).

JANUARY = 1

FEBRUARY

MARCH

APRIL

MAY

JUNE

JULY

AUGUST

SEPTEMBER

OCTOBER

NOVEMBER

DECEMBER

## Constructors

### DateTime

DateTime();

Creates a DateTime for the current date and time.

### DateTime

DateTime(
const Timestamp & timestamp
);

Creates a DateTime for the date and time given in a Timestamp.

### DateTime

DateTime(
double julianDay
);

Creates a DateTime for the given Julian day.

### DateTime

DateTime(
const DateTime & dateTime
);

Copy constructor. Creates the DateTime from another one.

### DateTime

DateTime(
Timestamp::UtcTimeVal utcTime,
Timestamp::TimeDiff diff
);

Creates a DateTime from an UtcTimeVal and a TimeDiff.

Mainly used internally by DateTime and friends.

### DateTime

DateTime(
int year,
int month,
int day,
int hour = 0,
int minute = 0,
int second = 0,
int millisecond = 0,
int microsecond = 0
);

Creates a DateTime for the given Gregorian date and time.

- year is from 0 to 9999.
- month is from 1 to 12.
- day is from 1 to 31.
- hour is from 0 to 23.
- minute is from 0 to 59.
- second is from 0 to 59.
- millisecond is from 0 to 999.
- microsecond is from 0 to 999.

## Destructor

### ~DateTime

~DateTime();

Destroys the DateTime.

## Member Functions

### assign

DateTime & assign(
int year,
int month,
int day,
int hour = 0,
int minute = 0,
int second = 0,
int millisecond = 0,
int microseconds = 0
);

Assigns a Gregorian date and time.

- year is from 0 to 9999.
- month is from 1 to 12.
- day is from 1 to 31.
- hour is from 0 to 23.
- minute is from 0 to 59.
- second is from 0 to 59.
- millisecond is from 0 to 999.
- microsecond is from 0 to 999.

### day

int day() const;

Returns the day witin the month (1 to 31).

### dayOfWeek

int dayOfWeek() const;

Returns the weekday (0 to 6, where 0 = Sunday, 1 = Monday, ..., 6 = Saturday).

### dayOfYear

int dayOfYear() const;

Returns the number of the day in the year. January 1 is 1, February 1 is 32, etc.

### daysOfMonth

static int daysOfMonth(
int year,
int month
);

Returns the number of days in the given month and year. Month is from 1 to 12.

### hour

int hour() const;

Returns the hour (0 to 23).

### hourAMPM

int hourAMPM() const;

Returns the hour (0 to 12).

### isAM

bool isAM() const;

Returns true if hour < 12;

### isLeapYear

static bool isLeapYear(
int year
);

Returns true if the given year is a leap year; false otherwise.

### isPM

bool isPM() const;

Returns true if hour >= 12.

### isValid

static bool isValid(
int year,
int month,
int day,
int hour = 0,
int minute = 0,
int second = 0,
int millisecond = 0,
int microsecond = 0
);

Checks if the given date and time is valid (all arguments are within a proper range).

Returns true if all arguments are valid, false otherwise.

### julianDay

double julianDay() const;

Returns the julian day for the date and time.

### makeLocal

void makeLocal(
int tzd
);

Converts a UTC time into a local time, by applying the given time zone differential.

### makeUTC

void makeUTC(
int tzd
);

Converts a local time into UTC, by applying the given time zone differential.

### microsecond

int microsecond() const;

Returns the microsecond (0 to 999)

### millisecond

int millisecond() const;

Returns the millisecond (0 to 999)

### minute

int minute() const;

Returns the minute (0 to 59).

### month

int month() const;

Returns the month (1 to 12).

### operator !=

bool operator != (
const DateTime & dateTime
) const;

### operator +

DateTime operator + (
const Timespan & span
) const;

### operator +=

DateTime & operator += (
const Timespan & span
);

### operator -

DateTime operator - (
const Timespan & span
) const;

### operator -

Timespan operator - (
const DateTime & dateTime
) const;

### operator -=

DateTime & operator -= (
const Timespan & span
);

### operator <

bool operator < (
const DateTime & dateTime
) const;

### operator <=

bool operator <= (
const DateTime & dateTime
) const;

### operator =

DateTime & operator = (
const DateTime & dateTime
);

Assigns another DateTime.

### operator =

DateTime & operator = (
const Timestamp & timestamp
);

Assigns a Timestamp.

### operator =

DateTime & operator = (
double julianDay
);

Assigns a Julian day.

### operator ==

bool operator == (
const DateTime & dateTime
) const;

### operator >

bool operator > (
const DateTime & dateTime
) const;

### operator >=

bool operator >= (
const DateTime & dateTime
) const;

### second

int second() const;

Returns the second (0 to 59).

### swap

void swap(
DateTime & dateTime
);

Swaps the DateTime with another one.

### timestamp

Timestamp timestamp() const;

Returns the date and time expressed as a Timestamp.

### utcTime

Timestamp::UtcTimeVal utcTime() const;

Returns the date and time expressed in UTC-based time. UTC base time is midnight, October 15, 1582. Resolution is 100 nanoseconds.

### week

int week(
int firstDayOfWeek = MONDAY
) const;

Returns the week number within the year. FirstDayOfWeek should be either SUNDAY (0) or MONDAY (1). The returned week number will be from 0 to 53. Week number 1 is the week containing January 4. This is in accordance to ISO 8601.

The following example assumes that firstDayOfWeek is MONDAY. For 2005, which started on a Saturday, week 1 will be the week starting on Monday, January 3. January 1 and 2 will fall within week 0 (or the last week of the previous year).

For 2007, which starts on a Monday, week 1 will be the week startung on Monday, January 1. There will be no week 0 in 2007.

### year

int year() const;

Returns the year.

### computeDaytime

void computeDaytime();

Extracts the daytime (hours, minutes, seconds, etc.) from the stored utcTime.

### computeGregorian

void computeGregorian(
double julianDay
);

Computes the Gregorian date for the given Julian day. See <http://vsg.cape.com/~pbaum/date/injdimp.htm>, section 3.3.1 for the algorithm.

### toJulianDay

static double toJulianDay(
Timestamp::UtcTimeVal utcTime
);

Computes the Julian day for an UTC time.

### toJulianDay

static double toJulianDay(
int year,
int month,
int day,
int hour = 0,
int minute = 0,
int second = 0,
int millisecond = 0,
int microsecond = 0
);

Computes the Julian day for a gregorian calendar date and time. See <http://vsg.cape.com/~pbaum/date/jdimp.htm>, section 2.3.1 for the algorithm.

### toUtcTime

static Timestamp::UtcTimeVal toUtcTime(
double julianDay
);

Computes the UTC time for a Julian day.