/src/corelib/tools/qdatetime.cpp

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#include "qplatformdefs.h"
#include "private/qdatetime_p.h"

#include "qdatastream.h"
#include "qset.h"
#include "qlocale.h"
#include "qdatetime.h"
#include "qregexp.h"
#include "qdebug.h"
#ifndef Q_OS_WIN
#include <locale.h>
#endif

#include <cmath>
#include <time.h>
#ifdef Q_OS_WIN
#  include <qt_windows.h>
#  ifdef Q_OS_WINCE
#    include "qfunctions_wince.h"
#  endif
#endif

//#define QDATETIMEPARSER_DEBUG
#if defined (QDATETIMEPARSER_DEBUG) && !defined(QT_NO_DEBUG_STREAM)
#  define QDTPDEBUG qDebug() << QString("%1:%2").arg(__FILE__).arg(__LINE__)
#  define QDTPDEBUGN qDebug
#else
#  define QDTPDEBUG if (false) qDebug()
#  define QDTPDEBUGN if (false) qDebug
#endif

#if defined(Q_OS_MAC)
#include <private/qcore_mac_p.h>
#endif

QT_BEGIN_NAMESPACE

enum {
    SECS_PER_DAY = 86400,
    MSECS_PER_DAY = 86400000,
    SECS_PER_HOUR = 3600,
    MSECS_PER_HOUR = 3600000,
    SECS_PER_MIN = 60,
    MSECS_PER_MIN = 60000,
    JULIAN_DAY_FOR_EPOCH = 2440588 // result of julianDayFromDate(1970, 1, 1)
};

static inline QDate fixedDate(int y, int m, int d)
{
    QDate result(y, m, 1);
    result.setDate(y, m, qMin(d, result.daysInMonth()));
    return result;
}

static inline qint64 floordiv(qint64 a, qint64 b)
{
    return (a - (a < 0 ? b-1 : 0)) / b;
}

static inline qint64 floordiv(qint64 a, int b)
{
    return (a - (a < 0 ? b-1 : 0)) / b;
}

static inline int floordiv(int a, int b)
{
    return (a - (a < 0 ? b-1 : 0)) / b;
}

static inline qint64 julianDayFromDate(int year, int month, int day)
{
    // Adjust for no year 0
    if (year < 0)
        ++year;

/*
 * Math from The Calendar FAQ at http://www.tondering.dk/claus/cal/julperiod.php
 * This formula is correct for all julian days, when using mathematical integer
 * division (round to negative infinity), not c++11 integer division (round to zero)
 */
    int    a = floordiv(14 - month, 12);
    qint64 y = (qint64)year + 4800 - a;
    int    m = month + 12 * a - 3;
    return day + floordiv(153 * m + 2, 5) + 365 * y + floordiv(y, 4) - floordiv(y, 100) + floordiv(y, 400) - 32045;
}

static void getDateFromJulianDay(qint64 julianDay, int *yearp, int *monthp, int *dayp)
{
/*
 * Math from The Calendar FAQ at http://www.tondering.dk/claus/cal/julperiod.php
 * This formula is correct for all julian days, when using mathematical integer
 * division (round to negative infinity), not c++11 integer division (round to zero)
 */
    qint64 a = julianDay + 32044;
    qint64 b = floordiv(4 * a + 3, 146097);
    int    c = a - floordiv(146097 * b, 4);

    int    d = floordiv(4 * c + 3, 1461);
    int    e = c - floordiv(1461 * d, 4);
    int    m = floordiv(5 * e + 2, 153);

    int    day = e - floordiv(153 * m + 2, 5) + 1;
    int    month = m + 3 - 12 * floordiv(m, 10);
    int    year = 100 * b + d - 4800 + floordiv(m, 10);

    // Adjust for no year 0
    if (year <= 0)
        --year ;

    if (yearp)
        *yearp = year;
    if (monthp)
        *monthp = month;
    if (dayp)
        *dayp = day;
}


static const char monthDays[] = { 0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

#ifndef QT_NO_TEXTDATE
static const char * const qt_shortMonthNames[] = {
    "Jan", "Feb", "Mar", "Apr", "May", "Jun",
    "Jul", "Aug", "Sep", "Oct", "Nov", "Dec" };
#endif
#ifndef QT_NO_DATESTRING
static QString fmtDateTime(const QString& f, const QTime* dt = 0, const QDate* dd = 0);
#endif

/*****************************************************************************
  QDate member functions
 *****************************************************************************/

/*!
    \since 4.5

    \enum QDate::MonthNameType

    This enum describes the types of the string representation used
    for the month name.

    \value DateFormat This type of name can be used for date-to-string formatting.
    \value StandaloneFormat This type is used when you need to enumerate months or weekdays.
           Usually standalone names are represented in singular forms with
           capitalized first letter.
*/

/*!
    \class QDate
    \inmodule QtCore
    \reentrant
    \brief The QDate class provides date functions.


    A QDate object contains a calendar date, i.e. year, month, and day
    numbers, in the Gregorian calendar. It can read the current date
    from the system clock. It provides functions for comparing dates,
    and for manipulating dates. For example, it is possible to add
    and subtract days, months, and years to dates.

    A QDate object is typically created by giving the year,
    month, and day numbers explicitly. Note that QDate interprets two
    digit years as is, i.e., years 0 - 99. A QDate can also be
    constructed with the static function currentDate(), which creates
    a QDate object containing the system clock's date.  An explicit
    date can also be set using setDate(). The fromString() function
    returns a QDate given a string and a date format which is used to
    interpret the date within the string.

    The year(), month(), and day() functions provide access to the
    year, month, and day numbers. Also, dayOfWeek() and dayOfYear()
    functions are provided. The same information is provided in
    textual format by the toString(), shortDayName(), longDayName(),
    shortMonthName(), and longMonthName() functions.

    QDate provides a full set of operators to compare two QDate
    objects where smaller means earlier, and larger means later.

    You can increment (or decrement) a date by a given number of days
    using addDays(). Similarly you can use addMonths() and addYears().
    The daysTo() function returns the number of days between two
    dates.

    The daysInMonth() and daysInYear() functions return how many days
    there are in this date's month and year, respectively. The
    isLeapYear() function indicates whether a date is in a leap year.

    \section1

    \section2 No Year 0

    There is no year 0. Dates in that year are considered invalid. The
    year -1 is the year "1 before Christ" or "1 before current era."
    The day before 1 January 1 CE is 31 December 1 BCE.

    \section2 Range of Valid Dates

    Dates are stored internally as a Julian Day number, an integer count of
    every day in a contiguous range, with 24 November 4714 BCE in the Gregorian
    calendar being Julian Day 0 (1 January 4713 BCE in the Julian calendar).
    As well as being an efficient and accurate way of storing an absolute date,
    it is suitable for converting a Date into other calendar systems such as
    Hebrew, Islamic or Chinese. The Julian Day number can be obtained using
    QDate::toJulianDay() and can be set using QDate::fromJulianDay().

    The range of dates able to be stored by QDate as a Julian Day number is
    for technical reasons limited to between -784350574879 and 784354017364,
    which means from before 2 billion BCE to after 2 billion CE.

    \sa QTime, QDateTime, QDateEdit, QDateTimeEdit, QCalendarWidget
*/

/*!
    \fn QDate::QDate()

    Constructs a null date. Null dates are invalid.

    \sa isNull(), isValid()
*/

/*!
    Constructs a date with year \a y, month \a m and day \a d.

    If the specified date is invalid, the date is not set and
    isValid() returns false.

    \warning Years 0 to 99 are interpreted as is, i.e., years
             0-99.

    \sa isValid()
*/

QDate::QDate(int y, int m, int d)
{
    setDate(y, m, d);
}


/*!
    \fn bool QDate::isNull() const

    Returns true if the date is null; otherwise returns false. A null
    date is invalid.

    \note The behavior of this function is equivalent to isValid().

    \sa isValid()
*/


/*!
    \fn bool QDate::isValid() const

    Returns true if this date is valid; otherwise returns false.

    \sa isNull()
*/


/*!
    Returns the year of this date. Negative numbers indicate years
    before 1 CE, such that year -44 is 44 BCE.

    Returns 0 if the date is invalid.

    \sa month(), day()
*/

int QDate::year() const
{
    if (isNull())
        return 0;

    int y;
    getDateFromJulianDay(jd, &y, 0, 0);
    return y;
}

/*!
    Returns the number corresponding to the month of this date, using
    the following convention:

    \list
    \li 1 = "January"
    \li 2 = "February"
    \li 3 = "March"
    \li 4 = "April"
    \li 5 = "May"
    \li 6 = "June"
    \li 7 = "July"
    \li 8 = "August"
    \li 9 = "September"
    \li 10 = "October"
    \li 11 = "November"
    \li 12 = "December"
    \endlist

    Returns 0 if the date is invalid.

    \sa year(), day()
*/

int QDate::month() const
{
    if (isNull())
        return 0;

    int m;
    getDateFromJulianDay(jd, 0, &m, 0);
    return m;
}

/*!
    Returns the day of the month (1 to 31) of this date.

    Returns 0 if the date is invalid.

    \sa year(), month(), dayOfWeek()
*/

int QDate::day() const
{
    if (isNull())
        return 0;

    int d;
    getDateFromJulianDay(jd, 0, 0, &d);
    return d;
}

/*!
    Returns the weekday (1 = Monday to 7 = Sunday) for this date.

    Returns 0 if the date is invalid.

    \sa day(), dayOfYear(), Qt::DayOfWeek
*/

int QDate::dayOfWeek() const
{
    if (isNull())
        return 0;

    if (jd >= 0)
        return (jd % 7) + 1;
    else
        return ((jd + 1) % 7) + 7;
}

/*!
    Returns the day of the year (1 to 365 or 366 on leap years) for
    this date.

    Returns 0 if the date is invalid.

    \sa day(), dayOfWeek()
*/

int QDate::dayOfYear() const
{
    if (isNull())
        return 0;

    return jd - julianDayFromDate(year(), 1, 1) + 1;
}

/*!
    Returns the number of days in the month (28 to 31) for this date.

    Returns 0 if the date is invalid.

    \sa day(), daysInYear()
*/

int QDate::daysInMonth() const
{
    if (isNull())
        return 0;

    int y, m;
    getDateFromJulianDay(jd, &y, &m, 0);
    if (m == 2 && isLeapYear(y))
        return 29;
    else
        return monthDays[m];
}

/*!
    Returns the number of days in the year (365 or 366) for this date.

    Returns 0 if the date is invalid.

    \sa day(), daysInMonth()
*/

int QDate::daysInYear() const
{
    if (isNull())
        return 0;

    int y;
    getDateFromJulianDay(jd, &y, 0, 0);
    return isLeapYear(y) ? 366 : 365;
}

/*!
    Returns the week number (1 to 53), and stores the year in
    *\a{yearNumber} unless \a yearNumber is null (the default).

    Returns 0 if the date is invalid.

    In accordance with ISO 8601, weeks start on Monday and the first
    Thursday of a year is always in week 1 of that year. Most years
    have 52 weeks, but some have 53.

    *\a{yearNumber} is not always the same as year(). For example, 1
    January 2000 has week number 52 in the year 1999, and 31 December
    2002 has week number 1 in the year 2003.

    \legalese
    Copyright (c) 1989 The Regents of the University of California.
    All rights reserved.

    Redistribution and use in source and binary forms are permitted
    provided that the above copyright notice and this paragraph are
    duplicated in all such forms and that any documentation,
    advertising materials, and other materials related to such
    distribution and use acknowledge that the software was developed
    by the University of California, Berkeley.  The name of the
    University may not be used to endorse or promote products derived
    from this software without specific prior written permission.
    THIS SOFTWARE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR
    IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
    WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.

    \sa isValid()
*/

int QDate::weekNumber(int *yearNumber) const
{
    if (!isValid())
        return 0;

    int year = QDate::year();
    int yday = dayOfYear() - 1;
    int wday = dayOfWeek();
    if (wday == 7)
        wday = 0;
    int w;

    for (;;) {
        int len;
        int bot;
        int top;

        len = isLeapYear(year) ? 366 : 365;
        /*
        ** What yday (-3 ... 3) does
        ** the ISO year begin on?
        */
        bot = ((yday + 11 - wday) % 7) - 3;
        /*
        ** What yday does the NEXT
        ** ISO year begin on?
        */
        top = bot - (len % 7);
        if (top < -3)
            top += 7;
        top += len;
        if (yday >= top) {
            ++year;
            w = 1;
            break;
        }
        if (yday >= bot) {
            w = 1 + ((yday - bot) / 7);
            break;
        }
        --year;
        yday += isLeapYear(year) ? 366 : 365;
    }
    if (yearNumber != 0)
        *yearNumber = year;
    return w;
}

#ifndef QT_NO_TEXTDATE
/*!
    \since 4.5

    Returns the short name of the \a month for the representation specified
    by \a type.

    The months are enumerated using the following convention:

    \list
    \li 1 = "Jan"
    \li 2 = "Feb"
    \li 3 = "Mar"
    \li 4 = "Apr"
    \li 5 = "May"
    \li 6 = "Jun"
    \li 7 = "Jul"
    \li 8 = "Aug"
    \li 9 = "Sep"
    \li 10 = "Oct"
    \li 11 = "Nov"
    \li 12 = "Dec"
    \endlist

    The month names will be localized according to the system's locale
    settings.

    Returns an empty string if the date is invalid.

    \sa toString(), longMonthName(), shortDayName(), longDayName()
*/

QString QDate::shortMonthName(int month, QDate::MonthNameType type)
{
    if (month < 1 || month > 12)
        return QString();

    switch (type) {
    case QDate::DateFormat:
        return QLocale::system().monthName(month, QLocale::ShortFormat);
    case QDate::StandaloneFormat:
        return QLocale::system().standaloneMonthName(month, QLocale::ShortFormat);
    default:
        break;
    }
    return QString();
}

/*!
    \since 4.5

    Returns the long name of the \a month for the representation specified
    by \a type.

    The months are enumerated using the following convention:

    \list
    \li 1 = "January"
    \li 2 = "February"
    \li 3 = "March"
    \li 4 = "April"
    \li 5 = "May"
    \li 6 = "June"
    \li 7 = "July"
    \li 8 = "August"
    \li 9 = "September"
    \li 10 = "October"
    \li 11 = "November"
    \li 12 = "December"
    \endlist

    The month names will be localized according to the system's locale
    settings.

    Returns an empty string if the date is invalid.

    \sa toString(), shortMonthName(), shortDayName(), longDayName()
*/

QString QDate::longMonthName(int month, MonthNameType type)
{
    if (month < 1 || month > 12)
        return QString();

    switch (type) {
    case QDate::DateFormat:
        return QLocale::system().monthName(month, QLocale::LongFormat);
    case QDate::StandaloneFormat:
        return QLocale::system().standaloneMonthName(month, QLocale::LongFormat);
    default:
        break;
    }
    return QString();
}

/*!
    \since 4.5

    Returns the short name of the \a weekday for the representation specified
    by \a type.

    The days are enumerated using the following convention:

    \list
    \li 1 = "Mon"
    \li 2 = "Tue"
    \li 3 = "Wed"
    \li 4 = "Thu"
    \li 5 = "Fri"
    \li 6 = "Sat"
    \li 7 = "Sun"
    \endlist

    The day names will be localized according to the system's locale
    settings.

    Returns an empty string if the date is invalid.

    \sa toString(), shortMonthName(), longMonthName(), longDayName()
*/

QString QDate::shortDayName(int weekday, MonthNameType type)
{
    if (weekday < 1 || weekday > 7)
        return QString();

    switch (type) {
    case QDate::DateFormat:
        return QLocale::system().dayName(weekday, QLocale::ShortFormat);
    case QDate::StandaloneFormat:
        return QLocale::system().standaloneDayName(weekday, QLocale::ShortFormat);
    default:
        break;
    }
    return QString();
}

/*!
    \since 4.5

    Returns the long name of the \a weekday for the representation specified
    by \a type.

    The days are enumerated using the following convention:

    \list
    \li 1 = "Monday"
    \li 2 = "Tuesday"
    \li 3 = "Wednesday"
    \li 4 = "Thursday"
    \li 5 = "Friday"
    \li 6 = "Saturday"
    \li 7 = "Sunday"
    \endlist

    The day names will be localized according to the system's locale
    settings.

    Returns an empty string if the date is invalid.

    \sa toString(), shortDayName(), shortMonthName(), longMonthName()
*/

QString QDate::longDayName(int weekday, MonthNameType type)
{
    if (weekday < 1 || weekday > 7)
        return QString();

    switch (type) {
    case QDate::DateFormat:
        return QLocale::system().dayName(weekday, QLocale::LongFormat);
    case QDate::StandaloneFormat:
        return QLocale::system().standaloneDayName(weekday, QLocale::LongFormat);
    default:
        break;
    }
    return QLocale::system().dayName(weekday, QLocale::LongFormat);
}
#endif //QT_NO_TEXTDATE

#ifndef QT_NO_DATESTRING

/*!
    \fn QString QDate::toString(Qt::DateFormat format) const

    \overload

    Returns the date as a string. The \a format parameter determines
    the format of the string.

    If the \a format is Qt::TextDate, the string is formatted in
    the default way. QDate::shortDayName() and QDate::shortMonthName()
    are used to generate the string, so the day and month names will
    be localized names. An example of this formatting is
    "Sat May 20 1995".

    If the \a format is Qt::ISODate, the string format corresponds
    to the ISO 8601 extended specification for representations of
    dates and times, taking the form YYYY-MM-DD, where YYYY is the
    year, MM is the month of the year (between 01 and 12), and DD is
    the day of the month between 01 and 31.

    If the \a format is Qt::SystemLocaleShortDate or
    Qt::SystemLocaleLongDate, the string format depends on the locale
    settings of the system. Identical to calling
    QLocale::system().toString(date, QLocale::ShortFormat) or
    QLocale::system().toString(date, QLocale::LongFormat).

    If the \a format is Qt::DefaultLocaleShortDate or
    Qt::DefaultLocaleLongDate, the string format depends on the
    default application locale. This is the locale set with
    QLocale::setDefault(), or the system locale if no default locale
    has been set. Identical to calling QLocale().toString(date,
    QLocale::ShortFormat) or QLocale().toString(date,
    QLocale::LongFormat).

    If the date is invalid, an empty string will be returned.

    \warning The Qt::ISODate format is only valid for years in the
    range 0 to 9999. This restriction may apply to locale-aware
    formats as well, depending on the locale settings.

    \sa shortDayName(), shortMonthName()
*/
QString QDate::toString(Qt::DateFormat f) const
{
    if (!isValid())
        return QString();
    int y, m, d;
    getDateFromJulianDay(jd, &y, &m, &d);
    switch (f) {
    case Qt::SystemLocaleDate:
    case Qt::SystemLocaleShortDate:
    case Qt::SystemLocaleLongDate:
        return QLocale::system().toString(*this, f == Qt::SystemLocaleLongDate ? QLocale::LongFormat
                                                                               : QLocale::ShortFormat);
    case Qt::LocaleDate:
    case Qt::DefaultLocaleShortDate:
    case Qt::DefaultLocaleLongDate:
        return QLocale().toString(*this, f == Qt::DefaultLocaleLongDate ? QLocale::LongFormat
                                                                        : QLocale::ShortFormat);
    default:
#ifndef QT_NO_TEXTDATE
    case Qt::TextDate:
        {
            return QString::fromLatin1("%0 %1 %2 %3")
                .arg(shortDayName(dayOfWeek()))
                .arg(shortMonthName(m))
                .arg(d)
                .arg(y);
        }
#endif
    case Qt::ISODate:
        {
            if (year() < 0 || year() > 9999)
                return QString();
            QString year(QString::number(y).rightJustified(4, QLatin1Char('0')));
            QString month(QString::number(m).rightJustified(2, QLatin1Char('0')));
            QString day(QString::number(d).rightJustified(2, QLatin1Char('0')));
            return year + QLatin1Char('-') + month + QLatin1Char('-') + day;
        }
    }
}

/*!
    Returns the date as a string. The \a format parameter determines
    the format of the result string.

    These expressions may be used:

    \table
    \header \li Expression \li Output
    \row \li d \li the day as number without a leading zero (1 to 31)
    \row \li dd \li the day as number with a leading zero (01 to 31)
    \row \li ddd
         \li the abbreviated localized day name (e.g. 'Mon' to 'Sun').
            Uses QDate::shortDayName().
    \row \li dddd
         \li the long localized day name (e.g. 'Monday' to 'Sunday').
            Uses QDate::longDayName().
    \row \li M \li the month as number without a leading zero (1 to 12)
    \row \li MM \li the month as number with a leading zero (01 to 12)
    \row \li MMM
         \li the abbreviated localized month name (e.g. 'Jan' to 'Dec').
            Uses QDate::shortMonthName().
    \row \li MMMM
         \li the long localized month name (e.g. 'January' to 'December').
            Uses QDate::longMonthName().
    \row \li yy \li the year as two digit number (00 to 99)
    \row \li yyyy \li the year as four digit number. If the year is negative,
            a minus sign is prepended in addition.
    \endtable

    All other input characters will be ignored. Any sequence of characters that
    are enclosed in single quotes will be treated as text and not be used as an
    expression. Two consecutive single quotes ("''") are replaced by a singlequote
    in the output. Formats without separators (e.g. "ddMM") are currently not supported.

    Example format strings (assuming that the QDate is the 20 July
    1969):

    \table
    \header \li Format            \li Result
    \row    \li dd.MM.yyyy        \li 20.07.1969
    \row    \li ddd MMMM d yy     \li Sun July 20 69
    \row    \li 'The day is' dddd \li The day is Sunday
    \endtable

    If the datetime is invalid, an empty string will be returned.

    \warning The Qt::ISODate format is only valid for years in the
    range 0 to 9999. This restriction may apply to locale-aware
    formats as well, depending on the locale settings.

    \sa QDateTime::toString(), QTime::toString()

*/
QString QDate::toString(const QString& format) const
{
    if (year() > 9999)
        return QString();
    return fmtDateTime(format, 0, this);
}
#endif //QT_NO_DATESTRING

/*!
    \fn bool QDate::setYMD(int y, int m, int d)

    \deprecated in 5.0, use setDate() instead.

    Sets the date's year \a y, month \a m, and day \a d.

    If \a y is in the range 0 to 99, it is interpreted as 1900 to
    1999.
    Returns \c false if the date is invalid.

    Use setDate() instead.
*/

/*!
    \since 4.2

    Sets the date's \a year, \a month, and \a day. Returns true if
    the date is valid; otherwise returns false.

    If the specified date is invalid, the QDate object is set to be
    invalid.

    \sa isValid()
*/
bool QDate::setDate(int year, int month, int day)
{
    if (isValid(year, month, day))
        jd = julianDayFromDate(year, month, day);
    else
        jd = nullJd();

    return isValid();
}

/*!
    \since 4.5

    Extracts the date's year, month, and day, and assigns them to
    *\a year, *\a month, and *\a day. The pointers may be null.

    Returns 0 if the date is invalid.

    \sa year(), month(), day(), isValid()
*/
void QDate::getDate(int *year, int *month, int *day)
{
    if (isValid()) {
        getDateFromJulianDay(jd, year, month, day);
    } else {
        if (year)
            *year = 0;
        if (month)
            *month = 0;
        if (day)
            *day = 0;
    }
}

/*!
    Returns a QDate object containing a date \a ndays later than the
    date of this object (or earlier if \a ndays is negative).

    Returns a null date if the current date is invalid or the new date is
    out of range.

    \sa addMonths(), addYears(), daysTo()
*/

QDate QDate::addDays(qint64 ndays) const
{
    if (isNull())
        return QDate();

    // Due to limits on minJd() and maxJd() we know that any overflow
    // will be invalid and caught by fromJulianDay().
    return fromJulianDay(jd + ndays);
}

/*!
    Returns a QDate object containing a date \a nmonths later than the
    date of this object (or earlier if \a nmonths is negative).

    \note If the ending day/month combination does not exist in the
    resulting month/year, this function will return a date that is the
    latest valid date.

    \sa addDays(), addYears()
*/

QDate QDate::addMonths(int nmonths) const
{
    if (!isValid())
        return QDate();
    if (!nmonths)
        return *this;

    int old_y, y, m, d;
    getDateFromJulianDay(jd, &y, &m, &d);
    old_y = y;

    bool increasing = nmonths > 0;

    while (nmonths != 0) {
        if (nmonths < 0 && nmonths + 12 <= 0) {
            y--;
            nmonths+=12;
        } else if (nmonths < 0) {
            m+= nmonths;
            nmonths = 0;
            if (m <= 0) {
                --y;
                m += 12;
            }
        } else if (nmonths - 12 >= 0) {
            y++;
            nmonths -= 12;
        } else if (m == 12) {
            y++;
            m = 0;
        } else {
            m += nmonths;
            nmonths = 0;
            if (m > 12) {
                ++y;
                m -= 12;
            }
        }
    }

    // was there a sign change?
    if ((old_y > 0 && y <= 0) ||
        (old_y < 0 && y >= 0))
        // yes, adjust the date by +1 or -1 years
        y += increasing ? +1 : -1;

    return fixedDate(y, m, d);
}

/*!
    Returns a QDate object containing a date \a nyears later than the
    date of this object (or earlier if \a nyears is negative).

    \note If the ending day/month combination does not exist in the
    resulting year (i.e., if the date was Feb 29 and the final year is
    not a leap year), this function will return a date that is the
    latest valid date (that is, Feb 28).

    \sa addDays(), addMonths()
*/

QDate QDate::addYears(int nyears) const
{
    if (!isValid())
        return QDate();

    int y, m, d;
    getDateFromJulianDay(jd, &y, &m, &d);

    int old_y = y;
    y += nyears;

    // was there a sign change?
    if ((old_y > 0 && y <= 0) ||
        (old_y < 0 && y >= 0))
        // yes, adjust the date by +1 or -1 years
        y += nyears > 0 ? +1 : -1;

    return fixedDate(y, m, d);
}

/*!
    Returns the number of days from this date to \a d (which is
    negative if \a d is earlier than this date).

    Returns 0 if either date is invalid.

    Example:
    \snippet code/src_corelib_tools_qdatetime.cpp 0

    \sa addDays()
*/

qint64 QDate::daysTo(const QDate &d) const
{
    if (isNull() || d.isNull())
        return 0;

    // Due to limits on minJd() and maxJd() we know this will never overflow
    return d.jd - jd;
}


/*!
    \fn bool QDate::operator==(const QDate &d) const

    Returns true if this date is equal to \a d; otherwise returns
    false.

*/

/*!
    \fn bool QDate::operator!=(const QDate &d) const

    Returns true if this date is different from \a d; otherwise
    returns false.
*/

/*!
    \fn bool QDate::operator<(const QDate &d) const

    Returns true if this date is earlier than \a d; otherwise returns
    false.
*/

/*!
    \fn bool QDate::operator<=(const QDate &d) const

    Returns true if this date is earlier than or equal to \a d;
    otherwise returns false.
*/

/*!
    \fn bool QDate::operator>(const QDate &d) const

    Returns true if this date is later than \a d; otherwise returns
    false.
*/

/*!
    \fn bool QDate::operator>=(const QDate &d) const

    Returns true if this date is later than or equal to \a d;
    otherwise returns false.
*/

/*!
    \fn QDate::currentDate()
    Returns the current date, as reported by the system clock.

    \sa QTime::currentTime(), QDateTime::currentDateTime()
*/

#ifndef QT_NO_DATESTRING
/*!
    \fn QDate QDate::fromString(const QString &string, Qt::DateFormat format)

    Returns the QDate represented by the \a string, using the
    \a format given, or an invalid date if the string cannot be
    parsed.

    Note for Qt::TextDate: It is recommended that you use the
    English short month names (e.g. "Jan"). Although localized month
    names can also be used, they depend on the user's locale settings.
*/
QDate QDate::fromString(const QString& s, Qt::DateFormat f)
{
    if (s.isEmpty())
        return QDate();

    switch (f) {
    case Qt::ISODate:
        {
            int year(s.mid(0, 4).toInt());
            int month(s.mid(5, 2).toInt());
            int day(s.mid(8, 2).toInt());
            if (year && month && day)
                return QDate(year, month, day);
        }
        break;
    case Qt::SystemLocaleDate:
    case Qt::SystemLocaleShortDate:
    case Qt::SystemLocaleLongDate:
        return fromString(s, QLocale::system().dateFormat(f == Qt::SystemLocaleLongDate ? QLocale::LongFormat
                                                                                        : QLocale::ShortFormat));
    case Qt::LocaleDate:
    case Qt::DefaultLocaleShortDate:
    case Qt::DefaultLocaleLongDate:
        return fromString(s, QLocale().dateFormat(f == Qt::DefaultLocaleLongDate ? QLocale::LongFormat
                                                                                 : QLocale::ShortFormat));
    default:
#ifndef QT_NO_TEXTDATE
    case Qt::TextDate: {
        QStringList parts = s.split(QLatin1Char(' '), QString::SkipEmptyParts);

        if (parts.count() != 4) {
            return QDate();
        }

        QString monthName = parts.at(1);
        int month = -1;
        // Assume that English monthnames are the default
        for (int i = 0; i < 12; ++i) {
            if (monthName == QLatin1String(qt_shortMonthNames[i])) {
                month = i + 1;
                break;
            }
        }
        // If English names can't be found, search the localized ones
        if (month == -1) {
            for (int i = 1; i <= 12; ++i) {
                if (monthName == QDate::shortMonthName(i)) {
                    month = i;
                    break;
                }
            }
            if (month == -1) {
                // Month name matches neither English nor other localised name.
                return QDate();
            }
        }

        bool ok;
        int day = parts.at(2).toInt(&ok);
        if (!ok) {
            return QDate();
        }

        int year = parts.at(3).toInt(&ok);
        if (!ok) {
            return QDate();
        }

        return QDate(year, month, day);
    }
#else
        break;
#endif
    }
    return QDate();
}

/*!
    \fn QDate::fromString(const QString &string, const QString &format)

    Returns the QDate represented by the \a string, using the \a
    format given, or an invalid date if the string cannot be parsed.

    These expressions may be used for the format:

    \table
    \header \li Expression \li Output
    \row \li d \li The day as a number without a leading zero (1 to 31)
    \row \li dd \li The day as a number with a leading zero (01 to 31)
    \row \li ddd
         \li The abbreviated localized day name (e.g. 'Mon' to 'Sun').
            Uses QDate::shortDayName().
    \row \li dddd
         \li The long localized day name (e.g. 'Monday' to 'Sunday').
            Uses QDate::longDayName().
    \row \li M \li The month as a number without a leading zero (1 to 12)
    \row \li MM \li The month as a number with a leading zero (01 to 12)
    \row \li MMM
         \li The abbreviated localized month name (e.g. 'Jan' to 'Dec').
            Uses QDate::shortMonthName().
    \row \li MMMM
         \li The long localized month name (e.g. 'January' to 'December').
            Uses QDate::longMonthName().
    \row \li yy \li The year as two digit number (00 to 99)
    \row \li yyyy \li The year as four digit number. If the year is negative,
            a minus sign is prepended in addition.
    \endtable

    All other input characters will be treated as text. Any sequence
    of characters that are enclosed in single quotes will also be
    treated as text and will not be used as an expression. For example:

    \snippet code/src_corelib_tools_qdatetime.cpp 1

    If the format is not satisfied, an invalid QDate is returned. The
    expressions that don't expect leading zeroes (d, M) will be
    greedy. This means that they will use two digits even if this
    will put them outside the accepted range of values and leaves too
    few digits for other sections. For example, the following format
    string could have meant January 30 but the M will grab two
    digits, resulting in an invalid date:

    \snippet code/src_corelib_tools_qdatetime.cpp 2

    For any field that is not represented in the format the following
    defaults are used:

    \table
    \header \li Field  \li Default value
    \row    \li Year   \li 1900
    \row    \li Month  \li 1
    \row    \li Day    \li 1
    \endtable

    The following examples demonstrate the default values:

    \snippet code/src_corelib_tools_qdatetime.cpp 3

    \sa QDateTime::fromString(), QTime::fromString(), QDate::toString(),
        QDateTime::toString(), QTime::toString()
*/

QDate QDate::fromString(const QString &string, const QString &format)
{
    QDate date;
#ifndef QT_BOOTSTRAPPED
    QDateTimeParser dt(QVariant::Date, QDateTimeParser::FromString);
    if (dt.parseFormat(format))
        dt.fromString(string, &date, 0);
#else
    Q_UNUSED(string);
    Q_UNUSED(format);
#endif
    return date;
}
#endif // QT_NO_DATESTRING

/*!
    \overload

    Returns true if the specified date (\a year, \a month, and \a
    day) is valid; otherwise returns false.

    Example:
    \snippet code/src_corelib_tools_qdatetime.cpp 4

    \sa isNull(), setDate()
*/

bool QDate::isValid(int year, int month, int day)
{
    // there is no year 0 in the Gregorian calendar
    if (year == 0)
        return false;

    return (day > 0 && month > 0 && month <= 12) &&
           (day <= monthDays[month] || (day == 29 && month == 2 && isLeapYear(year)));
}

/*!
    \fn bool QDate::isLeapYear(int year)

    Returns true if the specified \a year is a leap year; otherwise
    returns false.
*/

bool QDate::isLeapYear(int y)
{
    // No year 0 in Gregorian calendar, so -1, -5, -9 etc are leap years
    if ( y < 1)
        ++y;

    return (y % 4 == 0 && y % 100 != 0) || y % 400 == 0;
}

/*! \fn static QDate QDate::fromJulianDay(qint64 jd)

    Converts the Julian day \a jd to a QDate.

    \sa toJulianDay()
*/

/*! \fn int QDate::toJulianDay() const

    Converts the date to a Julian day.

    \sa fromJulianDay()
*/

/*****************************************************************************
  QTime member functions
 *****************************************************************************/

/*!
    \class QTime
    \inmodule QtCore
    \reentrant

    \brief The QTime class provides clock time functions.


    A QTime object contains a clock time, i.e. the number of hours,
    minutes, seconds, and milliseconds since midnight. It can read the
    current time from the system clock and measure a span of elapsed
    time. It provides functions for comparing times and for
    manipulating a time by adding a number of milliseconds.

    QTime uses the 24-hour clock format; it has no concept of AM/PM.
    Unlike QDateTime, QTime knows nothing about time zones or
    daylight savings time (DST).

    A QTime object is typically created either by giving the number
    of hours, minutes, seconds, and milliseconds explicitly, or by
    using the static function currentTime(), which creates a QTime
    object that contains the system's local time. Note that the
    accuracy depends on the accuracy of the underlying operating
    system; not all systems provide 1-millisecond accuracy.

    The hour(), minute(), second(), and msec() functions provide
    access to the number of hours, minutes, seconds, and milliseconds
    of the time. The same information is provided in textual format by
    the toString() function.

    QTime provides a full set of operators to compare two QTime
    objects. QTime A is considered smaller than QTime B if A is
    earlier than B.

    The addSecs() and addMSecs() functions provide the time a given
    number of seconds or milliseconds later than a given time.
    Correspondingly, the number of seconds or milliseconds
    between two times can be found using secsTo() or msecsTo().

    QTime can be used to measure a span of elapsed time using the
    start(), restart(), and elapsed() functions.

    \sa QDate, QDateTime
*/

/*!
    \fn QTime::QTime()

    Constructs a null time object. A null time can be a QTime(0, 0, 0, 0)
    (i.e., midnight) object, except that isNull() returns true and isValid()
    returns false.

    \sa isNull(), isValid()
*/

/*!
    Constructs a time with hour \a h, minute \a m, seconds \a s and
    milliseconds \a ms.

    \a h must be in the range 0 to 23, \a m and \a s must be in the
    range 0 to 59, and \a ms must be in the range 0 to 999.

    \sa isValid()
*/

QTime::QTime(int h, int m, int s, int ms)
{
    setHMS(h, m, s, ms);
}


/*!
    \fn bool QTime::isNull() const

    Returns true if the time is null (i.e., the QTime object was
    constructed using the default constructor); otherwise returns
    false. A null time is also an invalid time.

    \sa isValid()
*/

/*!
    Returns true if the time is valid; otherwise returns false. For example,
    the time 23:30:55.746 is valid, but 24:12:30 is invalid.

    \sa isNull()
*/

bool QTime::isValid() const
{
    return mds > NullTime && mds < MSECS_PER_DAY;
}


/*!
    Returns the hour part (0 to 23) of the time.

    Returns -1 if the time is invalid.

    \sa minute(), second(), msec()
*/

int QTime::hour() const
{
    if (!isValid())
        return -1;

    return ds() / MSECS_PER_HOUR;
}

/*!
    Returns the minute part (0 to 59) of the time.

    Returns -1 if the time is invalid.

    \sa hour(), second(), msec()
*/

int QTime::minute() const
{
    if (!isValid())
        return -1;

    return (ds() % MSECS_PER_HOUR) / MSECS_PER_MIN;
}

/*!
    Returns the second part (0 to 59) of the time.

    Returns -1 if the time is invalid.

    \sa hour(), minute(), msec()
*/

int QTime::second() const
{
    if (!isValid())
        return -1;

    return (ds() / 1000)%SECS_PER_MIN;
}

/*!
    Returns the millisecond part (0 to 999) of the time.

    Returns -1 if the time is invalid.

    \sa hour(), minute(), second()
*/

int QTime::msec() const
{
    if (!isValid())
        return -1;

    return ds() % 1000;
}

#ifndef QT_NO_DATESTRING
/*!
    \overload

    Returns the time as a string. Milliseconds are not included. The
    \a format parameter determines the format of the string.

    If \a format is Qt::TextDate, the string format is HH:MM:SS; e.g. 1
    second before midnight would be "23:59:59".

    If \a format is Qt::ISODate, the string format corresponds to the
    ISO 8601 extended specification for representations of dates,
    which is also HH:MM:SS. (However, contrary to ISO 8601, dates
    before 15 October 1582 are handled as Julian dates, not Gregorian
    dates. See \l{QDate G and J} {Use of Gregorian and Julian
    Calendars}. This might change in a future version of Qt.)

    If the \a format is Qt::SystemLocaleShortDate or
    Qt::SystemLocaleLongDate, the string format depends on the locale
    settings of the system. Identical to calling
    QLocale::system().toString(time, QLocale::ShortFormat) or
    QLocale::system().toString(time, QLocale::LongFormat).

    If the \a format is Qt::DefaultLocaleShortDate or
    Qt::DefaultLocaleLongDate, the string format depends on the
    default application locale. This is the locale set with
    QLocale::setDefault(), or the system locale if no default locale
    has been set. Identical to calling QLocale().toString(time,
    QLocale::ShortFormat) or QLocale().toString(time,
    QLocale::LongFormat).

    If the time is invalid, an empty string will be returned.
*/

QString QTime::toString(Qt::DateFormat format) const
{
    if (!isValid())
        return QString();

    switch (format) {
    case Qt::SystemLocaleDate:
    case Qt::SystemLocaleShortDate:
    case Qt::SystemLocaleLongDate:
        return QLocale::system().toString(*this, format == Qt::SystemLocaleLongDate ? QLocale::LongFormat
                                          : QLocale::ShortFormat);
    case Qt::LocaleDate:
    case Qt::DefaultLocaleShortDate:
    case Qt::DefaultLocaleLongDate:
        return QLocale().toString(*this, format == Qt::DefaultLocaleLongDate ? QLocale::LongFormat
                                  : QLocale::ShortFormat);

    default:
    case Qt::ISODate:
    case Qt::TextDate:
        return QString::fromLatin1("%1:%2:%3")
            .arg(hour(), 2, 10, QLatin1Char('0'))
            .arg(minute(), 2, 10, QLatin1Char('0'))
            .arg(second(), 2, 10, QLatin1Char('0'));
    }
}

/*!
    Returns the time as a string. The \a format parameter determines
    the format of the result string.

    These expressions may be used:

    \table
    \header \li Expression \li Output
    \row \li h
         \li the hour without a leading zero (0 to 23 or 1 to 12 if AM/PM display)
    \row \li hh
         \li the hour with a leading zero (00 to 23 or 01 to 12 if AM/PM display)
    \row \li H
         \li the hour without a leading zero (0 to 23, even with AM/PM display)
    \row \li HH
         \li the hour with a leading zero (00 to 23, even with AM/PM display)
    \row \li m \li the minute without a leading zero (0 to 59)
    \row \li mm \li the minute with a leading zero (00 to 59)
    \row \li s \li the second without a leading zero (0 to 59)
    \row \li ss \li the second with a leading zero (00 to 59)
    \row \li z \li the milliseconds without leading zeroes (0 to 999)
    \row \li zzz \li the milliseconds with leading zeroes (000 to 999)
    \row \li AP or A
         \li use AM/PM display. \e AP will be replaced by either "AM" or "PM".
    \row \li ap or a
         \li use am/pm display. \e ap will be replaced by either "am" or "pm".
    \row \li t \li the timezone (for example "CEST")
    \endtable

    All other input characters will be ignored. Any sequence of characters that
    are enclosed in single quotes will be treated as text and not be used as an
    expression. Two consecutive single quotes ("''") are replaced by a singlequote
    in the output. Formats without separators (e.g. "HHmm") are currently not supported.

    Example format strings (assuming that the QTime is 14:13:09.042)

    \table
    \header \li Format \li Result
    \row \li hh:mm:ss.zzz \li 14:13:09.042
    \row \li h:m:s ap     \li 2:13:9 pm
    \row \li H:m:s a      \li 14:13:9 pm
    \endtable

    If the time is invalid, an empty string will be returned.
    If \a format is empty, the default format "hh:mm:ss" is used.

    \sa QDate::toString(), QDateTime::toString()
*/
QString QTime::toString(const QString& format) const
{
    return fmtDateTime(format, this, 0);
}
#endif //QT_NO_DATESTRING
/*!
    Sets the time to hour \a h, minute \a m, seconds \a s and
    milliseconds \a ms.

    \a h must be in the range 0 to 23, \a m and \a s must be in the
    range 0 to 59, and \a ms must be in the range 0 to 999.
    Returns true if the set time is valid; otherwise returns false.

    \sa isValid()
*/

bool QTime::setHMS(int h, int m, int s, int ms)
{
#if defined(Q_OS_WINCE)
    startTick = NullTime;
#endif
    if (!isValid(h,m,s,ms)) {
        mds = NullTime;                // make this invalid
        return false;
    }
    mds = (h*SECS_PER_HOUR + m*SECS_PER_MIN + s)*1000 + ms;
    return true;
}

/*!
    Returns a QTime object containing a time \a s seconds later
    than the time of this object (or earlier if \a s is negative).

    Note that the time will wrap if it passes midnight.

    Returns a null time if this time is invalid.

    Example:

    \snippet code/src_corelib_tools_qdatetime.cpp 5

    \sa addMSecs(), secsTo(), QDateTime::addSecs()
*/

QTime QTime::addSecs(int s) const
{
    return addMSecs(s * 1000);
}

/*!
    Returns the number of seconds from this time to \a t.
    If \a t is earlier than this time, the number of seconds returned
    is negative.

    Because QTime measures time within a day and there are 86400
    seconds in a day, the result is always between -86400 and 86400.

    secsTo() does not take into account any milliseconds.

    Returns 0 if either time is invalid.

    \sa addSecs(), QDateTime::secsTo()
*/

int QTime::secsTo(const QTime &t) const
{
    if (!isValid() || !t.isValid())
        return 0;

    // Truncate milliseconds as we do not want to consider them.
    int ourSeconds = ds() / 1000;
    int theirSeconds = t.ds() / 1000;
    return theirSeconds - ourSeconds;
}

/*!
    Returns a QTime object containing a time \a ms milliseconds later
    than the time of this object (or earlier if \a ms is negative).

    Note that the time will wrap if it passes midnight. See addSecs()
    for an example.

    Returns a null time if this time is invalid.

    \sa addSecs(), msecsTo(), QDateTime::addMSecs()
*/

QTime QTime::addMSecs(int ms) const
{
    QTime t;
    if (isValid()) {
        if (ms < 0) {
            // % not well-defined for -ve, but / is.
            int negdays = (MSECS_PER_DAY - ms) / MSECS_PER_DAY;
            t.mds = (ds() + ms + negdays * MSECS_PER_DAY) % MSECS_PER_DAY;
        } else {
            t.mds = (ds() + ms) % MSECS_PER_DAY;
        }
    }
#if defined(Q_OS_WINCE)
    if (startTick > NullTime)
        t.startTick = (startTick + ms) % MSECS_PER_DAY;
#endif
    return t;
}

/*!
    Returns the number of milliseconds from this time to \a t.
    If \a t is earlier than this time, the number of milliseconds returned
    is negative.

    Because QTime measures time within a day and there are 86400
    seconds in a day, the result is always between -86400000 and
    86400000 ms.

    Returns 0 if either time is invalid.

    \sa secsTo(), addMSecs(), QDateTime::msecsTo()
*/

int QTime::msecsTo(const QTime &t) const
{
    if (!isValid() || !t.isValid())
        return 0;
#if defined(Q_OS_WINCE)
    // GetLocalTime() for Windows CE has no milliseconds resolution
    if (t.startTick > NullTime && startTick > NullTime)
        return t.startTick - startTick;
    else
#endif
        return t.ds() - ds();
}


/*!
    \fn bool QTime::operator==(const QTime &t) const

    Returns true if this time is equal to \a t; otherwise returns false.
*/

/*!
    \fn bool QTime::operator!=(const QTime &t) const

    Returns true if this time is different from \a t; otherwise returns false.
*/

/*!
    \fn bool QTime::operator<(const QTime &t) const

    Returns true if this time is earlier than \a t; otherwise returns false.
*/

/*!
    \fn bool QTime::operator<=(const QTime &t) const

    Returns true if this time is earlier than or equal to \a t;
    otherwise returns false.
*/

/*!
    \fn bool QTime::operator>(const QTime &t) const

    Returns true if this time is later than \a t; otherwise returns false.
*/

/*!
    \fn bool QTime::operator>=(const QTime &t) const

    Returns true if this time is later than or equal to \a t;
    otherwise returns false.
*/

/*!
    \fn QTime::currentTime()

    Returns the current time as reported by the system clock.

    Note that the accuracy depends on the accuracy of the underlying
    operating system; not all systems provide 1-millisecond accuracy.
*/

#ifndef QT_NO_DATESTRING

// These anonymous functions tidy up QDateTime::fromString()
// and avoid confusion of responsibility between it and QTime::fromString().
namespace {
inline bool isMidnight(int hour, int minute, int second, int msec)
{
    return hour == 24 && minute == 0 && second == 0 && msec == 0;
}

QTime fromStringImpl(const QString &s, Qt::DateFormat f, bool &isMidnight24)
{
    if (s.isEmpty()) {
        // Return a null time.
        return QTime();
    }

    …

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