Why does the QMultiMap function not work as I expected?
I have QMultiMap<QDateTime, SomeOwnDataType>
one from which I would like to get all values with a specific timestamp. This is what I am doing:
QMap<QDateTime, Appointment>::iterator it = _reminders.find(now);
where now
is di 6.mrt 12:07:00 2012. This is my loop condition:
while (it != _reminders.end() && it.key() == now) {
This was the state of the object _reminders
:
Contrary to my expectations, the cycle was skipped entirely. Why?
source to share
I believe the problem is that the two timestamps are not equal. If you check the operator code ==
QDateTime
, you can see that equality is satisfied if both time and date values are equal.
bool QDateTime::operator==(const QDateTime &other) const
{
if (d->spec == other.d->spec && d->utcOffset == other.d->utcOffset)
return d->time == other.d->time && d->date == other.d->date;
else {
QDate date1, date2;
QTime time1, time2;
d->getUTC(date1, time1);
other.d->getUTC(date2, time2);
return time1 == time2 && date1 == date2;
}
}
But the equal time operator compares milliseconds:
bool operator==(const QTime &other) const { return mds == other.mds; }
where mds
is the time in milliseconds. QTime
mds
Calculated in the constructor as follows:
mds = (h*SECS_PER_HOUR + m*SECS_PER_MIN + s)*1000 + ms;
It would be safer if you only check if the difference between the two timestamps is within the limit. For example:
while (it != _reminders.end() && abs(now.msecsTo(it.key())) < aLimitInMsecs) {
source to share
How do you initialize now
?
QDateTime
increases to a millisecond, so it toString()
can display the same value, while in fact the values are different ... If at some point the key _reminders [0] is not set to a value now
, they will be different.
If you are creating a calendar application, you can use it QString
as a key to yours QMultiMap
, and the values will be displayed QDateTime::toString()
(the format depends on the precision you want (day, hour, minute, ...)
source to share