Develop Reference

DateTime manipulation

Here is my code:
DateTime startDate = Convert.ToDateTime( orderDate ).AddMonths(-1);
DateTime endDate = Convert.ToDateTime( orderDate );
orderDate is a valid date I pass in.
How do I always guarantee startDate is the first day of the previous month for orderDate?
How do I always guarantee endDate is the last day of the month for orderDate?
Example:
orderDate = 5/4/2012
I want startDate to be 4/1/2012 (or 04/1/2012 whichever is default)
I want endDate to be 4/30/2012
How can I acheive this?

DateTime startDate = Convert.ToDateTime( orderDate ).AddMonths(-1);
// set to first of month
startDate = startDate.AddDays(1-startDate.Day);
// Set end date to last of month, which is one day before first of next month
DateTime endDate = startDate.AddMonths(1).AddDays(-1);

origDate = startDate.AddMonths(-1);
DateTime myDate = new DateTime(origDate.Year, origDate.Month, 1);
http://msdn.microsoft.com/en-us/library/xcfzdy4x.aspx
Something like this... We do it often enough that we've just created an extension method on date.

DateTime startDate = new DateTime( orderDate.Month == 1 ? orderDate.Year - 1 : orderDate.Year, orderDate.Month - 1, 1);
DateTime endDate = new DateTime(orderDate.Year, orderDate.Month, DateTime.DaysInMonth(orderDate.Year, OrderDate.Month));

Use DateTime constructor that takes separate values for each year, month, day,... and adjust them accodringly (i.e. first of the month means day = 1).

var orderDate = DateTime.Now.Date;
var endDate = orderDate.AddDays(-orderDate.Day);
var startDate = endDate.AddDays(-(endDate.Day - 1));

How to get All Dates in a given month in C#

I want to make a function that take month and year and return List<DateTime> filled with all dates in this month.
any help will be appreciated
Thanks in Advance

Here's a solution with LINQ:
public static List<DateTime> GetDates(int year, int month)
{
return Enumerable.Range(1, DateTime.DaysInMonth(year, month)) // Days: 1, 2 ... 31 etc.
.Select(day => new DateTime(year, month, day)) // Map each day to a date
.ToList(); // Load dates into a list
}
And one with a for-loop:
public static List<DateTime> GetDates(int year, int month)
{
var dates = new List<DateTime>();
// Loop from the first day of the month until we hit the next month, moving forward a day at a time
for (var date = new DateTime(year, month, 1); date.Month == month; date = date.AddDays(1))
{
dates.Add(date);
}
return dates;
}
You might want to consider returning a streaming sequence of dates instead of List<DateTime>, letting the caller decide whether to load the dates into a list or array / post-process them / partially iterate them etc. For the LINQ version, you can accomplish this by removing the call to ToList(). For the for-loop, you would want to implement an iterator. In both cases, the return-type would have to be changed to IEnumerable<DateTime>.

Sample for pre-Linq Framework versions, using February 1999.
int year = 1999;
int month = 2;
List<DateTime> list = new List<DateTime>();
DateTime date = new DateTime(year, month, 1);
do
{
list.Add(date);
date = date.AddDays(1);
while (date.Month == month);

I am sure there might be better ways to do this. But, you could use this:
public List<DateTime> getAllDates(int year, int month)
{
var ret = new List<DateTime>();
for (int i=1; i<=DateTime.DaysInMonth(year,month); i++) {
ret.Add(new DateTime(year, month, i));
}
return ret;
}

Here you go:
public List<DateTime> AllDatesInAMonth(int month, int year)
{
var firstOftargetMonth = new DateTime(year, month, 1);
var firstOfNextMonth = firstOftargetMonth.AddMonths(1);
var allDates = new List<DateTime>();
for (DateTime date = firstOftargetMonth; date < firstOfNextMonth; date = date.AddDays(1) )
{
allDates.Add(date);
}
return allDates;
}
Iterates through the dates from the first of the month you want through to the last date that's less than the first of the next month.
PS: If this is homework, please tag it with "homework"!

Getting all DateTimes between two 'DateTime's in C#

I have two DateTimes, and I want to get all DateTimes between these Dates. Such as, if my Dates are like 01.01.2010 - 05.01.2010, my function should return me a list of date (List), and it must contain 01.01.2010, 02.01.2010, 03.01.2010, 04.01.2010, and 05.01.2010.
I wrote a function like this. It works fine, if my dates are in a month. It won't work if my dates are like 01.01.2010 - 05.02.2010. Because the month changed, and my function can't handle it. Is there a function in C# that returns all dates between two dates? Or how can I handle month change?
public void GetAllDatesAndInitializeTickets(DateTime startingDate, DateTime endingDate)
{
List<DateTime> allDates = new List<DateTime>();
int starting = startingDate.Day;
int ending = endingDate.Day;
for (int i = starting; i <= ending; i++)
{
allDates.Add(new DateTime(startingDate.Year, startingDate.Month, i));
}
Question solved, see Tim Robinson's simple answer to use.

You can use DateTime objects directly in the loop, in place of your int. DateTime.AddDays handles month ends correctly.
for (DateTime date = startingDate; date <= endingDate; date = date.AddDays(1))
allDates.Add(date);

How about something like this?
public IEnumerable<DateTime> DateRange(DateTime fromDate, DateTime toDate)
{
return Enumerable.Range(0, toDate.Subtract(fromDate).Days + 1)
.Select(d => fromDate.AddDays(d));
}
Edit: Tested now. :)

public IEnumerable<DateTime> GetAllDatesAndInitializeTickets(DateTime startingDate, DateTime endingDate)
{
if (endingDate < startingDate)
{
throw new ArgumentException("endingDate should be after startingDate");
}
var ts = endingDate - startingDate;
for (int i = 0; i < ts.TotalDays; i++)
{
yield return startingDate.AddDays(i);
}
}

You were so close... just don't use the day, use the whole date.
static IEnumerable<DateTime> GetAllDatesAndInitializeTickets(DateTime startingDate, DateTime endingDate)
{
List<DateTime> allDates = new List<DateTime>();
for (DateTime i = startingDate; i <= endingDate; i = i.AddDays(1))
{
allDates.Add(i);
}
return allDates.AsReadOnly();
}

Given a lowerdate value and higher date value in String and a frequency as the third parameter this method should return a dictionary of dates; where the key is the start value of a date range and the value is the respective range.
This works fine if the frequency is either weekly or monthly- you can customize it as per your need.
The date values passed should be in proper format or you might need to format it using tryParseExact or something like that.
protected static Dictionary<DateTime, String> getDateRange(String lowerDate, String higherDate, String frequency)
{
DateTime startDate, endDate;
startDate = Convert.ToDateTime(lowerDate);
endDate = Convert.ToDateTime(higherDate);
Dictionary<DateTime, String> returnDict = new Dictionary<DateTime, String>();
while (frequency.Equals("weekly") ? (startDate.AddDays(7) <= endDate) : (startDate.AddMonths(1) <= endDate))
{
if (frequency.Equals("weekly"))
{
returnDict.Add(startDate, startDate + "-" + startDate.AddDays(7));
startDate = startDate.AddDays(8);
}
if (frequency.Equals("monthly"))
{
returnDict.Add(startDate, startDate + "-" + startDate.AddMonths(1));
startDate = startDate.AddMonths(1).AddDays(1);
}
}
returnDict.Add(startDate, startDate + "-" + endDate);
return returnDict;
}

The top solutions will fail if the date includes different hours. Here is a solution getting all hours and all days:
All Days:
static public List<string> get_days_between_two_dates(DateTime start_date, DateTime end_date)
{
List<string> days_list = new List<string>();
DateTime temp_start;
DateTime temp_end;
//--Normalize dates by getting rid of minues since they will get in the way when doing the loop
temp_start = new DateTime(start_date.Year, start_date.Month, start_date.Day);
temp_end = new DateTime(end_date.Year, end_date.Month, end_date.Day);
//--Example Should return
//--1-12-2014 5:59AM - 1-13-2014 6:01AM return 12 and 13
for (DateTime date = temp_start; date <= temp_end; date = date.AddDays(1))
{
days_list.Add(date.ToShortDateString());
}
return days_list;
}
All Hours:
static public List<string> get_hours_between_two_dates(DateTime start_date, DateTime end_date)
{
List<string> hours_24_list = new List<string>();
DateTime temp_start;
DateTime temp_end;
//--Normalize dates by getting rid of minutes since they will get in the way when doing the loop
temp_start = new DateTime(start_date.Year, start_date.Month, start_date.Day, start_date.Hour, 0, 0);
temp_end = new DateTime(end_date.Year, end_date.Month, end_date.Day, end_date.Hour, 0, 0);
//--Example Should return
//--5:59AM - 6:01AM return 5am and 6am
for (DateTime date = temp_start; date <= temp_end; date = date.AddHours(1))
{
hours_24_list.Add(date.ToShortTimeString());
}
return hours_24_list;
}

Based on your starting code and using the features available at the time of writing, here is a quick console app to demonstrate how to do it - use AddDays() instead:
class Program
{
static void Main(string[] args)
{
GetDates(new DateTime(2010, 1, 1), new DateTime(2010, 2, 5));
Console.ReadKey();
}
static List<DateTime> GetDates(DateTime startDate, DateTime endDate)
{
List<DateTime> dates = new List<DateTime>();
while ((startDate = startDate.AddDays(1)) < endDate)
dates.Add(startDate);
return dates;
}
}
Although I think the Enumerable.Range() answer from Matt is a nicer solution.

static IEnumerable<DateTime> GetAllDatesAndInitializeTickets(DateTime startingDate, DateTime endingDate)
{
List<DateTime> allDates = new List<DateTime>();
for (DateTime i = startingDate; i <= endingDate; i = i.AddDays(1))
{
allDates.Add(i);
}
return allDates.AsReadOnly();
}

How do I loop through a date range?

I'm not even sure how to do this without using some horrible for loop/counter type solution. Here's the problem:
I'm given two dates, a start date and an end date and on a specified interval I need to take some action. For example: for every date between 3/10/2009 on every third day until 3/26/2009 I need to create an entry in a List. So my inputs would be:
DateTime StartDate = "3/10/2009";
DateTime EndDate = "3/26/2009";
int DayInterval = 3;
and my output would be a list that has the following dates:
3/13/2009
3/16/2009
3/19/2009
3/22/2009
3/25/2009
So how the heck would I do something like this? I thought about using a for loop that would iterate between every day in the range with a separate counter like so:
int count = 0;
for(int i = 0; i < n; i++)
{
count++;
if(count >= DayInterval)
{
//take action
count = 0;
}
}
But it seems like there could be a better way?

Well, you'll need to loop over them one way or the other. I prefer defining a method like this:
public IEnumerable<DateTime> EachDay(DateTime from, DateTime thru)
{
for(var day = from.Date; day.Date <= thru.Date; day = day.AddDays(1))
yield return day;
}
Then you can use it like this:
foreach (DateTime day in EachDay(StartDate, EndDate))
// print it or whatever
In this manner you could hit every other day, every third day, only weekdays, etc. For example, to return every third day starting with the "start" date, you could just call AddDays(3) in the loop instead of AddDays(1).

I have a Range class in MiscUtil which you could find useful. Combined with the various extension methods, you could do:
foreach (DateTime date in StartDate.To(EndDate).ExcludeEnd()
.Step(DayInterval.Days())
{
// Do something with the date
}
(You may or may not want to exclude the end - I just thought I'd provide it as an example.)
This is basically a ready-rolled (and more general-purpose) form of mquander's solution.

For your example you can try
DateTime StartDate = new DateTime(2009, 3, 10);
DateTime EndDate = new DateTime(2009, 3, 26);
int DayInterval = 3;
List<DateTime> dateList = new List<DateTime>();
while (StartDate.AddDays(DayInterval) <= EndDate)
{
StartDate = StartDate.AddDays(DayInterval);
dateList.Add(StartDate);
}

Code from #mquander and #Yogurt The Wise used in extensions:
public static IEnumerable<DateTime> EachDay(DateTime from, DateTime thru)
{
for (var day = from.Date; day.Date <= thru.Date; day = day.AddDays(1))
yield return day;
}
public static IEnumerable<DateTime> EachMonth(DateTime from, DateTime thru)
{
for (var month = from.Date; month.Date <= thru.Date || month.Month == thru.Month; month = month.AddMonths(1))
yield return month;
}
public static IEnumerable<DateTime> EachDayTo(this DateTime dateFrom, DateTime dateTo)
{
return EachDay(dateFrom, dateTo);
}
public static IEnumerable<DateTime> EachMonthTo(this DateTime dateFrom, DateTime dateTo)
{
return EachMonth(dateFrom, dateTo);
}

1 Year later, may it help someone,
This version includes a predicate, to be more flexible.
Usage
var today = DateTime.UtcNow;
var birthday = new DateTime(2018, 01, 01);
Daily to my birthday
var toBirthday = today.RangeTo(birthday);
Monthly to my birthday, Step 2 months
var toBirthday = today.RangeTo(birthday, x => x.AddMonths(2));
Yearly to my birthday
var toBirthday = today.RangeTo(birthday, x => x.AddYears(1));
Use RangeFrom instead
// same result
var fromToday = birthday.RangeFrom(today);
var toBirthday = today.RangeTo(birthday);
Implementation
public static class DateTimeExtensions
{
public static IEnumerable<DateTime> RangeTo(this DateTime from, DateTime to, Func<DateTime, DateTime> step = null)
{
if (step == null)
{
step = x => x.AddDays(1);
}
while (from < to)
{
yield return from;
from = step(from);
}
}
public static IEnumerable<DateTime> RangeFrom(this DateTime to, DateTime from, Func<DateTime, DateTime> step = null)
{
return from.RangeTo(to, step);
}
}
Extras
You could throw an Exception if the fromDate > toDate, but I prefer to return an empty range instead []

DateTime startDate = new DateTime(2009, 3, 10);
DateTime stopDate = new DateTime(2009, 3, 26);
int interval = 3;
for (DateTime dateTime=startDate;
dateTime < stopDate;
dateTime += TimeSpan.FromDays(interval))
{
}

DateTime begindate = Convert.ToDateTime("01/Jan/2018");
DateTime enddate = Convert.ToDateTime("12 Feb 2018");
while (begindate < enddate)
{
begindate= begindate.AddDays(1);
Console.WriteLine(begindate + " " + enddate);
}

According to the problem you can try this...
// looping between date range
while (startDate <= endDate)
{
//here will be your code block...
startDate = startDate.AddDays(1);
}
thanks......

DateTime startDate = new DateTime(2009, 3, 10);
DateTime stopDate = new DateTime(2009, 3, 26);
int interval = 3;
while ((startDate = startDate.AddDays(interval)) <= stopDate)
{
// do your thing
}

Here are my 2 cents in 2020.
Enumerable.Range(0, (endDate - startDate).Days + 1)
.ToList()
.Select(a => startDate.AddDays(a));

You can use the DateTime.AddDays() function to add your DayInterval to the StartDate and check to make sure it is less than the EndDate.

You might consider writing an iterator instead, which allows you to use normal 'for' loop syntax like '++'. I searched and found a similar question answered here on StackOverflow which gives pointers on making DateTime iterable.

you have to be careful here not to miss the dates when in the loop a better solution would be.
this gives you the first date of startdate and use it in the loop before incrementing it and it will process all the dates including the last date of enddate hence <= enddate.
so the above answer is the correct one.
while (startdate <= enddate)
{
// do something with the startdate
startdate = startdate.adddays(interval);
}

you can use this.
DateTime dt0 = new DateTime(2009, 3, 10);
DateTime dt1 = new DateTime(2009, 3, 26);
for (; dt0.Date <= dt1.Date; dt0=dt0.AddDays(3))
{
//Console.WriteLine(dt0.Date.ToString("yyyy-MM-dd"));
//take action
}

Iterate every 15 minutes
DateTime startDate = DateTime.Parse("2018-06-24 06:00");
DateTime endDate = DateTime.Parse("2018-06-24 11:45");
while (startDate.AddMinutes(15) <= endDate)
{
Console.WriteLine(startDate.ToString("yyyy-MM-dd HH:mm"));
startDate = startDate.AddMinutes(15);
}

#jacob-sobus and #mquander and #Yogurt not exactly correct.. If I need the next day I wait 00:00 time mostly
public static IEnumerable<DateTime> EachDay(DateTime from, DateTime thru)
{
for (var day = from.Date; day.Date <= thru.Date; day = day.NextDay())
yield return day;
}
public static IEnumerable<DateTime> EachMonth(DateTime from, DateTime thru)
{
for (var month = from.Date; month.Date <= thru.Date || month.Year == thru.Year && month.Month == thru.Month; month = month.NextMonth())
yield return month;
}
public static IEnumerable<DateTime> EachYear(DateTime from, DateTime thru)
{
for (var year = from.Date; year.Date <= thru.Date || year.Year == thru.Year; year = year.NextYear())
yield return year;
}
public static DateTime NextDay(this DateTime date)
{
return date.AddTicks(TimeSpan.TicksPerDay - date.TimeOfDay.Ticks);
}
public static DateTime NextMonth(this DateTime date)
{
return date.AddTicks(TimeSpan.TicksPerDay * DateTime.DaysInMonth(date.Year, date.Month) - (date.TimeOfDay.Ticks + TimeSpan.TicksPerDay * (date.Day - 1)));
}
public static DateTime NextYear(this DateTime date)
{
var yearTicks = (new DateTime(date.Year + 1, 1, 1) - new DateTime(date.Year, 1, 1)).Ticks;
var ticks = (date - new DateTime(date.Year, 1, 1)).Ticks;
return date.AddTicks(yearTicks - ticks);
}
public static IEnumerable<DateTime> EachDayTo(this DateTime dateFrom, DateTime dateTo)
{
return EachDay(dateFrom, dateTo);
}
public static IEnumerable<DateTime> EachMonthTo(this DateTime dateFrom, DateTime dateTo)
{
return EachMonth(dateFrom, dateTo);
}
public static IEnumerable<DateTime> EachYearTo(this DateTime dateFrom, DateTime dateTo)
{
return EachYear(dateFrom, dateTo);
}

If you convert your dates to OADate you can loop thru them as you would do with any double number.
DateTime startDate = new DateTime(2022, 1, 1);
DateTime endDate = new DateTime(2022, 12, 31);
for (double loopDate = startDate.ToOADate(); loopDate <= endDate.ToOADate(); loopDate++)
{
DateTime selectedDate;
selectedDate = DateTime.FromOADate(loopDate);
}

Get the previous month's first and last day dates in c#

I can't think of an easy one or two liner that would get the previous months first day and last day.
I am LINQ-ifying a survey web app, and they squeezed a new requirement in.
The survey must include all of the service requests for the previous month. So if it is April 15th, I need all of Marches request ids.
var RequestIds = (from r in rdc.request
where r.dteCreated >= LastMonthsFirstDate &&
r.dteCreated <= LastMonthsLastDate
select r.intRequestId);
I just can't think of the dates easily without a switch. Unless I'm blind and overlooking an internal method of doing it.

var today = DateTime.Today;
var month = new DateTime(today.Year, today.Month, 1);
var first = month.AddMonths(-1);
var last = month.AddDays(-1);
In-line them if you really need one or two lines.

The way I've done this in the past is first get the first day of this month
dFirstDayOfThisMonth = DateTime.Today.AddDays( - ( DateTime.Today.Day - 1 ) );
Then subtract a day to get end of last month
dLastDayOfLastMonth = dFirstDayOfThisMonth.AddDays (-1);
Then subtract a month to get first day of previous month
dFirstDayOfLastMonth = dFirstDayOfThisMonth.AddMonths(-1);

using Fluent DateTime https://github.com/FluentDateTime/FluentDateTime
var lastMonth = 1.Months().Ago().Date;
var firstDayOfMonth = lastMonth.FirstDayOfMonth();
var lastDayOfMonth = lastMonth.LastDayOfMonth();

DateTime LastMonthLastDate = DateTime.Today.AddDays(0 - DateTime.Today.Day);
DateTime LastMonthFirstDate = LastMonthLastDate.AddDays(1 - LastMonthLastDate.Day);

I use this simple one-liner:
public static DateTime GetLastDayOfPreviousMonth(this DateTime date)
{
return date.AddDays(-date.Day);
}
Be aware, that it retains the time.

An approach using extension methods:
class Program
{
static void Main(string[] args)
{
DateTime t = DateTime.Now;
DateTime p = t.PreviousMonthFirstDay();
Console.WriteLine( p.ToShortDateString() );
p = t.PreviousMonthLastDay();
Console.WriteLine( p.ToShortDateString() );
Console.ReadKey();
}
}
public static class Helpers
{
public static DateTime PreviousMonthFirstDay( this DateTime currentDate )
{
DateTime d = currentDate.PreviousMonthLastDay();
return new DateTime( d.Year, d.Month, 1 );
}
public static DateTime PreviousMonthLastDay( this DateTime currentDate )
{
return new DateTime( currentDate.Year, currentDate.Month, 1 ).AddDays( -1 );
}
}
See this link
http://www.codeplex.com/fluentdatetime
for some inspired DateTime extensions.

The canonical use case in e-commerce is credit card expiration dates, MM/yy. Subtract one second instead of one day. Otherwise the card will appear expired for the entire last day of the expiration month.
DateTime expiration = DateTime.Parse("07/2013");
DateTime endOfTheMonthExpiration = new DateTime(
expiration.Year, expiration.Month, 1).AddMonths(1).AddSeconds(-1);

If there's any chance that your datetimes aren't strict calendar dates, you should consider using enddate exclusion comparisons...
This will prevent you from missing any requests created during the date of Jan 31.
DateTime now = DateTime.Now;
DateTime thisMonth = new DateTime(now.Year, now.Month, 1);
DateTime lastMonth = thisMonth.AddMonths(-1);
var RequestIds = rdc.request
.Where(r => lastMonth <= r.dteCreated)
.Where(r => r.dteCreated < thisMonth)
.Select(r => r.intRequestId);

DateTime now = DateTime.Now;
int prevMonth = now.AddMonths(-1).Month;
int year = now.AddMonths(-1).Year;
int daysInPrevMonth = DateTime.DaysInMonth(year, prevMonth);
DateTime firstDayPrevMonth = new DateTime(year, prevMonth, 1);
DateTime lastDayPrevMonth = new DateTime(year, prevMonth, daysInPrevMonth);
Console.WriteLine("{0} {1}", firstDayPrevMonth.ToShortDateString(),
lastDayPrevMonth.ToShortDateString());

This is a take on Mike W's answer:
internal static DateTime GetPreviousMonth(bool returnLastDayOfMonth)
{
DateTime firstDayOfThisMonth = DateTime.Today.AddDays( - ( DateTime.Today.Day - 1 ) );
DateTime lastDayOfLastMonth = firstDayOfThisMonth.AddDays (-1);
if (returnLastDayOfMonth) return lastDayOfLastMonth;
return firstDayOfThisMonth.AddMonths(-1);
}
You can call it like so:
dateTimePickerFrom.Value = GetPreviousMonth(false);
dateTimePickerTo.Value = GetPreviousMonth(true);

var lastMonth = DateTime.Today.AddMonths(-1);
dRet1 = new DateTime(lastMonth.Year, lastMonth.Month, 1);
dRet2 = new DateTime(lastMonth.Year, lastMonth.Month, DateTime.DaysInMonth(lastMonth.Year, lastMonth.Month));