C++ DateTime class - c++

Question

I have my own C++ DateTime class defined as:
class DateTime
{
public:
int year;
int month;
int day;
int hour;
int min;
int sec;
int millisec;
};
I have 2 DateTime which I need to compare to see which one is greater than (more recent) the other.
Is there any freely available C++ DateTime class that I can use to
Convert my DateTime class to their DateTime class
Their class should provide < , > , <= , >= operators for comparison
If a concrete example could be provided that would be great. Note that I need to compare down to millisecond.
I was thinking about Boost or Qt. Preferred Boost though.

Answer 1

See Boost Date Time library
And your class looks very much like struct tm
EDIT:
You're right that struct tm doesn't support millisecond precision.
Take a look at a Boost example. Does that help?

Answer 2

You may want to check out QDateTime from Qt, wich has the required operators and ms accuracy.
Conversion from your class could be done via
class DateTime
{
public:
int year;
int month;
int day;
int hour;
int min;
int sec;
int millisec;
QDateTime toQDateTime() {
return QDateTime(QDate(year, month, day), QTime(hour, min, sec, millisec));
}
};
The other way around is similar ;-)

Answer 3

I don't know of any off the top of my head. But I'd consider rewriting your date class to hold a single 64-bit integer describing milliseconds since the conventional epoch (1970 is it?). Then you are free to simply divide by 1000 and use the normal CRT functions for formatting as a string, plus you can take the value modulo 1000 to get the millisecond part.
Comparison operators then become easy..

Answer 4

I ditch storing dates in gregorian ages ago.
I store dates as an 32bit integer (sort of like a Julian date).
So the date is composed as (Year * 1000) + DOY (DOY is day of year).
I.e.
- 2009001 Is Jan 1 2009
- 2009365 is Dec 31 2009
My date class of course provides methods for getting the Year, Month and Day, adding, subtracting, incrementing and decrementing, comparing, getting the number of days between dates etc..
For date and time, I use 64bit float where the integer portion of the real number is the same as integer (Julian like) dates described above, and the fraction represents the time in fraction of a day.
I.e.
2009001.04166666666~ is Jan 1,2009 1:00am
2009001.06249999999~ is Jan 1,2009 1:30am
2009001.95833333333~ is Jan 1,2009 11:00pm
If you only need minute accuracy, you can use 32bit float
for date and time but you can't adequately accurately
store seconds and milliseconds.
The advantages of storing dates (and time) in this manner are:
You only need 8bytes to represent the data and time
as compared to 28bytes (assuming 32bit integers)
used by the DateTime class in the question.
Compared with dates stored as seconds from an epoch,
when looking at the number (for example in the debugger)
you can more or less identify from
the number the year and the day of year, and the approximate time of day
(to get the hour, minute, second
after midnight simply mulitply by 24, 1440, 86400 respectively).
Comparing dates is trivial, simply compare the numbers
(A single CPU operation compared to the several it
would take for the example DateTime).
Fewer comparison operations to do date arithmetic.
The disadvange of this (for time time) is a slight loss of accuracy (this is practically a mute point) and you have to do some simple rounding to get nice integer values when convering to integer values of hours minutes and seconds.

Answer 5

Okay, here's the final code snippet that answers my own question. I thought of sharing this in case it might helpful to some other people in the future. Thanks to Fred Larson for pointing the Boost example.
I chose Boost to do the DateTime calculation because my application already makes use of Boost somewhere else. I think I might have been able to use Qt as well, though I cant completely confirm.
Assuming DateTime is defined as:
class DateTime
{
public:
int year;
int month;
int day;
int hour;
int min;
int sec;
int millisec;
};
To do a simple DateTime comparison
bool DateTime::operator < (const DateTime& dt_)
{
using namespace boost::posix_time;
using namespace boost::gregorian;
ptime thisTime( date(this->year,this->month,this->day),
hours(this->hour) +
minutes(this->min) +
seconds(this->sec) +
boost::posix_time::millisec(int(this->millisec)) );
ptime thatTime( date(dt_.year,dt_.month,dt_.day),
hours(dt_.hour) +
minutes(dt_.min) +
seconds(dt_.sec) +
boost::posix_time::millisec(int(dt_.millisec)) );
return thisTime < thatTime;
}
To add 2 DateTime together to return a new DateTime
DateTime DateTime::operator + ( const DateTime& dt_ )
{
using namespace boost::posix_time;
using namespace boost::gregorian;
date thisDate( this->year, this->month, this->day );
date newDate = thisDate + years(dt_.year) + months(dt_.month) + days(dt_.day);
ptime newDateTime( newDate,
hours(this->hour) + hours(dt_.hour) +
minutes(this->min) + minutes(dt_.min) +
seconds(this->sec) + seconds(dt_.sec) +
boost::posix_time::millisec(int(this->millisec)) +
boost::posix_time::millisec(int(dt_.millisec))
);
DateTime dateTime;
date t1_date = newDateTime.date();
dateTime.year = t1_date.year();
dateTime.month = t1_date.month();
dateTime.day = t1_date.day();
time_duration t1_time = newDateTime.time_of_day();
dateTime.hour = t1_time.hours();
dateTime.min = t1_time.minutes();
dateTime.sec = t1_time.seconds();
dateTime.millisec = t1_time.fractional_seconds()/1000.0f;
return dateTime;
}

Answer 6

What's wrong with using the content of <time.h> for implementing your class? It's standard C90.

Answer 7

GNU R uses a struct tm replacement with microsecond precision -- instead of (integer) seconds since the epoch, it now uses a floating point number. That is really really useful. For many of my applications, I just past doubles around and yet get the time conversions.
See R-2.9.1/src/main/datetime.c in the current R sources.
Having that in a standalone C++ class would be handy though.

Answer 8

Look at
MFC datetime classes CTime and COleDateTime classes
More at http://www.codeproject.com/KB/datetime/datetimedisc.aspx