qdatetime.cpp

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  This function is guaranteed to be atomic, and is thus very handy for
  repeated measurements: call start() to start the first measurement,
  then restart() for each later measurement.

  Note that the counter wraps to zero 24 hours after the last call to
  start() or restart().

  \warning If the system's clock setting has been changed since the
  last time start() or restart() was called, the result is undefined.
  This can happen e.g. when daylight saving is turned on or off.

  \sa start(), elapsed(), currentTime()
*/

int QTime::restart()
{
    QTime t = currentTime();
    int n = msecsTo( t );
    if ( n < 0 )				// passed midnight
	n += 86400*1000;
    *this = t;
    return n;
}

/*!
  Returns the number of milliseconds that have elapsed since the last
  time start() or restart() was called.

  Note that the counter wraps to zero 24 hours after the last call to
  start() or restart.

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

  \warning If the system's clock setting has been changed since the
  last time start() or restart() was called, the result is undefined.
  This can happen e.g. when daylight saving is turned on or off.

  \sa start(), restart()
*/

int QTime::elapsed()
{
    int n = msecsTo( currentTime() );
    if ( n < 0 )				// passed midnight
	n += 86400*1000;
    return n;
}


/*****************************************************************************
  QDateTime member functions
 *****************************************************************************/

/*!
  \class QDateTime qdatetime.h
  \brief The QDateTime class provides date and time functions.

  \ingroup time

  A QDateTime object contains a calendar date and a clock time (a
  "datetime"). It is a combination of the QDate and QTime classes. It
  can read the current datetime from the system clock. It provides
  functions for comparing datetimes and for manipulating a datetime by
  adding a number of seconds or days.

  A QDateTime object is typically created either by giving a date and
  time explicitly, or by using the static function currentTime(),
  which makes a QDateTime object which contains the system's clock
  time.

  The date() and time() functions provide access to the date and time
  parts of the datetime. The same information is provided in textual
  format by the toString() function.

  QDateTime provides a full set of operators to compare two QDateTime
  objects. A datetime is considered smaller than another if it is
  earlier than the other.

  The datetime a given number of days or seconds later than a given
  datetime can be found using the addDays() and addSecs()
  functions. Correspondingly, the number of days or seconds between
  two times can be found using the daysTo() or secsTo() functions.

  A datetime can also be set using the setTime_t() function, which
  takes a POSIX-standard "number of seconds since 00:00:00 on January
  1, 1970" value.

  The limitations regarding range and resolution mentioned in the
  QDate and QTime documentation apply for QDateTime also.

  \sa QDate, QTime
*/


/*!
  \fn QDateTime::QDateTime()

  Constructs a null datetime (i.e. null date and null time).  A null
  datetime is invalid, since the date is invalid.

  \sa isValid()
*/


/*!
  Constructs a datetime with date \a date and null time (00:00:00.000).
*/

QDateTime::QDateTime( const QDate &date )
    : d(date)
{
}

/*!
  Constructs a datetime with date \a date and time \a time.
*/

QDateTime::QDateTime( const QDate &date, const QTime &time )
    : d(date), t(time)
{
}


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

  Returns TRUE if both the date and the time are null.	A null date is invalid.

  \sa QDate::isNull(), QTime::isNull()
*/

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

  Returns TRUE if both the date and the time are valid.

  \sa QDate::isValid(), QTime::isValid()
*/

/*!
  \fn QDate QDateTime::date() const

  Returns the date part of this datetime.

  \sa setDate(), time()
*/

/*!
  \fn QTime QDateTime::time() const

  Returns the time part of this datetime.

  \sa setTime(), date()
*/

/*!
  \fn void QDateTime::setDate( const QDate &date )

  Sets the date part of this datetime.

  \sa date(), setTime()
*/

/*!
  \fn void QDateTime::setTime( const QTime &time )

  Sets the time part of this datetime.

  \sa time(), setDate()
*/


/*!
  Sets the local date and time given the number of seconds that have passed
  since 00:00:00 on January 1, 1970, Coordinated Universal Time (UTC).
  On systems that do not support timezones this function will behave as if
  local time were UTC.

  Note that Microsoft Windows supports only a limited range of values for
  \a secsSince1Jan1970UTC.
*/

void QDateTime::setTime_t( uint secsSince1Jan1970UTC )
{
    time_t tmp = (time_t) secsSince1Jan1970UTC;
    tm *tM = localtime( &tmp );
    if ( !tM ) {
	tM = gmtime( &tmp );
	if ( !tM ) {
	    d.jd = QDate::greg2jul( 1970, 1, 1 );
	    t.ds = 0;
	    return;
	}
    }
    d.jd = QDate::greg2jul( tM->tm_year + 1900, tM->tm_mon + 1, tM->tm_mday );
    t.ds = MSECS_PER_HOUR*tM->tm_hour + MSECS_PER_MIN*tM->tm_min +
	    1000*tM->tm_sec;
}


/*!
  Returns the datetime as a string.

  The string format is "Sat May 20 03:40:13 1998".

  This function uses QDate::dayName(), QDate::monthName(), and
  QTime::toString() to generate the string.

*/

QString QDateTime::toString() const
{
    QString buf = d.dayName(d.dayOfWeek());
    buf += ' ';
    buf += d.monthName(d.month());
    buf += ' ';
    buf += QString().setNum(d.day());
    buf += ' ';
    buf += t.toString();
    buf += ' ';
    buf += QString().setNum(d.year());
    return buf;
}

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

  \sa daysTo(), addSecs()
*/

QDateTime QDateTime::addDays( int ndays ) const
{
    return QDateTime( d.addDays(ndays), t );
}

/*!
  Returns a QDateTime object containing a datetime \a nsecs seconds
  later than the datetime of this object (or earlier if \a nsecs is
  negative).

  \sa secsTo(), addDays()
*/

QDateTime QDateTime::addSecs( int nsecs ) const
{
    uint dd = d.jd;
    int  tt = t.ds;
    int  sign = 1;
    if ( nsecs < 0 ) {
	nsecs = -nsecs;
	sign = -1;
    }
    if ( nsecs >= (int)SECS_PER_DAY ) {
	dd += sign*(nsecs/SECS_PER_DAY);
	nsecs %= SECS_PER_DAY;
    }
    tt += sign*nsecs*1000;
    if ( tt < 0 ) {
	tt = MSECS_PER_DAY - tt - 1;
	dd -= tt / MSECS_PER_DAY;
	tt = tt % MSECS_PER_DAY;
	tt = MSECS_PER_DAY - tt - 1;
    } else if ( tt >= (int)MSECS_PER_DAY ) {
	dd += ( tt / MSECS_PER_DAY );
	tt = tt % MSECS_PER_DAY;
    }
    QDateTime ret;
    ret.t.ds = tt;
    ret.d.jd = dd;
    return ret;
}

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

  \sa addDays(), secsTo()
*/

int QDateTime::daysTo( const QDateTime &dt ) const
{
    return d.daysTo( dt.d );
}

/*!
  Returns the number of seconds from this datetime to \a dt (which is
  negative if \a dt is earlier than this datetime).

  Example:
  \code
    QDateTime dt = QDateTime::currentDateTime();
    QDateTime x( QDate(dt.year(),12,24), QTime(17,00) );
    qDebug( "There are %d seconds to Christmas", dt.secsTo(x) );
  \endcode

  \sa addSecs(), daysTo(), QTime::secsTo()
*/

int QDateTime::secsTo( const QDateTime &dt ) const
{
    return t.secsTo(dt.t) + d.daysTo(dt.d)*SECS_PER_DAY;
}


/*!
  Returns TRUE if this datetime is equal to \a dt, or FALSE if
  they are different.
  \sa operator!=()
*/

bool QDateTime::operator==( const QDateTime &dt ) const
{
    return  t == dt.t && d == dt.d;
}

/*!
  Returns TRUE if this datetime is different from \a dt, or FALSE if
  they are equal.
  \sa operator==()
*/

bool QDateTime::operator!=( const QDateTime &dt ) const
{
    return  t != dt.t || d != dt.d;
}

/*!
  Returns TRUE if this datetime is earlier than \a dt, otherwise FALSE.
*/

bool QDateTime::operator<( const QDateTime &dt ) const
{
    if ( d < dt.d )
	return TRUE;
    return d == dt.d ? t < dt.t : FALSE;
}

/*!
  Returns TRUE if this datetime is earlier than or equal to \a dt,
  otherwise FALSE.
*/

bool QDateTime::operator<=( const QDateTime &dt ) const
{
    if ( d < dt.d )
	return TRUE;
    return d == dt.d ? t <= dt.t : FALSE;
}

/*!
  Returns TRUE if this datetime is later than \a dt, otherwise FALSE.
*/

bool QDateTime::operator>( const QDateTime &dt ) const
{
    if ( d > dt.d )
	return TRUE;
    return d == dt.d ? t > dt.t : FALSE;
}

/*!
  Returns TRUE if this datetime is later than or equal to \a dt,
  otherwise FALSE.
*/

bool QDateTime::operator>=( const QDateTime &dt ) const
{
    if ( d > dt.d )
	return TRUE;
    return d == dt.d ? t >= dt.t : FALSE;
}

/*!
  Returns the current datetime, as reported by the system clock.

  \sa QDate::currentDate(), QTime::currentTime()
*/

QDateTime QDateTime::currentDateTime()
{
    QDate cd = QDate::currentDate();
    QTime ct;
    if ( QTime::currentTime(&ct) )		// too close to midnight?
	cd = QDate::currentDate();		// YES! time for some midnight
						// voodoo, fetch date again
    return QDateTime( cd, ct );
}


/*****************************************************************************
  Date/time stream functions
 *****************************************************************************/

#ifndef QT_NO_DATASTREAM
/*!
  \relates QDate
  Writes the date to the stream.

  \sa \link datastreamformat.html Format of the QDataStream operators \endlink
*/

QDataStream &operator<<( QDataStream &s, const QDate &d )
{
    return s << (Q_UINT32)(d.jd);
}

/*!
  \relates QDate
  Reads a date from the stream.

  \sa \link datastreamformat.html Format of the QDataStream operators \endlink
*/

QDataStream &operator>>( QDataStream &s, QDate &d )
{
    Q_UINT32 jd;
    s >> jd;
    d.jd = jd;
    return s;
}

/*!
  \relates QTime
  Writes a time to the stream.

  \sa \link datastreamformat.html Format of the QDataStream operators \endlink
*/

QDataStream &operator<<( QDataStream &s, const QTime &t )
{
    return s << (Q_UINT32)(t.ds);
}

/*!
  \relates QTime
  Reads a time from the stream.

  \sa \link datastreamformat.html Format of the QDataStream operators \endlink
*/

QDataStream &operator>>( QDataStream &s, QTime &t )
{
    Q_UINT32 ds;
    s >> ds;
    t.ds = ds;
    return s;
}

/*!
  \relates QDateTime
  Writes a datetime to the stream.

  \sa \link datastreamformat.html Format of the QDataStream operators \endlink
*/

QDataStream &operator<<( QDataStream &s, const QDateTime &dt )
{
    return s << dt.d << dt.t;
}

/*!
  \relates QDateTime
  Reads a datetime from the stream.

  \sa \link datastreamformat.html Format of the QDataStream operators \endlink
*/

QDataStream &operator>>( QDataStream &s, QDateTime &dt )
{
    s >> dt.d >> dt.t;
    return s;
}
#endif //QT_NO_DATASTREAM