Develop Reference

How to parse a Date and Time, separately, into a DateTime in C#?

I'm trying to parse two separate fields, a date and a time, into one DateTime object as strings. The date has padding, the time doesn't, but they follow a consistent format, with date being something like 07302018 and time being 101230; an issue being, as well, that time could be something like 91230. What I've tried right now:
string timeformat1 = "MMddyyyy HHmmss";
string timeformat2 = "MMddyyyy Hmmss";
string date = "07302018"
string time = "63020"
if (time.Length == 6)
{
datetimeobject = DateTime.ParseExact($"{date} {time}", timeformat1, CultureInfo.InvariantCulture);
}
else
{
datetimeobject = DateTime.ParseExact($"{date} {time}", timeformat2, CultureInfo.InvariantCulture);
}
Doesn't seem to work, giving a "String was not recognized as a valid DateTime" exception.
Am I going to need to insert some slashes and punctuation into the strings in order to make them read correctly? I wanted to avoid this because I had heard there are performance concerns with disassembling and reassembling strings, but I may have to do so unless there is a more elegant solution.

Try this to avoid ifs
string timeformat = "MMddyyyy HHmmss";
string date = "07302018";
string time = "91230";
string joint = $"{date} {time.PadLeft(6,'0')}";
DateTime datetimeobject = DateTime.ParseExact(joint, timeformat, System.Globalization.CultureInfo.InvariantCulture);
The DateTime.ParseExact will fail with a single char for hour and the single H because it need a separation between hour and other values. From MSDN:
If format is a custom format pattern that does not include date or
time separators (such as "yyyyMMddHHmm"), use the invariant culture
for the provider parameter and the widest form of each custom format
specifier. For example, if you want to specify hours in the format
pattern, specify the wider form, "HH", instead of the narrower form,
"H".

How to use DateTime to make a countdown calendar in C#

I'm currently learning C# and making some console applications.
I want to create a console app which take two dates as parameters (YEAR/MONTH/DAY).
One for the start, and another one for the end.
I've tried to make a difference between the two of them, but I get the following error message:
"Cannot implicitly convert type 'System.TimeSpan' to 'System.DateTime' [Calendar]"
Here's my code:
static void Main(string[] args)
{
DateTime t = DateTime.Now;
DateTime end = new DateTime(2017, 11, 17);
int result = DateTime.Compare(t, end);
TimeSpan timeSpan = end - t;
DateTime days_left = timeSpan;
Console.WriteLine("Left", timeSpan.TotalDays);
Console.ReadKey();
}
In this version, I enter the end date in the code.
Thanks in advance for your help and for your time,

The following line is the problem:
DateTime days_left = timeSpan;
When you declared timeSpan you gave it the type TimeSpan. On the very next line, you try to assign timeSpan to days_left, which is a variable of type DateTime. This is not possible, as you cannot directly cast one type to the other.
If you think about it, this line doesn't even make sense, as DateTime objects represent a date not a time span. That is what TimeSpan objects are for!
Simply remove that line and your program will compile no problem.
Also, if I may make a suggestion, do not directly subtract DateTimes like you have done here:
var timeSpan = end - t;
Instead use DateTime.Subtract:
var timeSpan = end.Subtract(t);
This is the recommended approach when dealing with the difference between DateTimes, as it offers benefits such as adjusting for different time zones.
Finally, note my usage of the var keyword instead of explicitly declaring the type. This is a common coding convention in C# that I wish I knew as a beginner.
Here is a revised version of your code. Take some tips from it if you want for programs you write in the future:
public static void Main()
{
var currentDate = DateTime.Now; // Descriptive variable names
var endDate = new DateTime(2017, 11, 17);
double remainingDays = endDate.Subtract(currentDate).TotalDays; //TimeSpan stores everything in doubles instead of integers
Console.WriteLine("Days left: {0}", remainingDays); // Use String.Format formatting
Console.ReadLine(); // Use readline so that program only exists when ENTER is pressed
}

Try changing your code to this
DateTime t = DateTime.Now;
DateTime end = new DateTime(2017, 11, 17);
int result = DateTime.Compare(t, end);
TimeSpan timeSpan = end.Subtract(t);

return date without time but not of type string but date

I have a date value that I want to strip the time from. I want the return type to be a date type since I want to order the list of date I have. having a list to string representing Date does not return a correct order.
I know that DateTime always returns the date with the time. What are my options here? How can I better my code and have a list of items of Date type without the time?
Edit: I would like to have the date only. nothing after that. Something like 8/7/2016 not 8/7/2016 00:00:00 or anything after date. and in a date object.
Here is my code:
using (var db = new MyModel.Context())
{
var cert = (
from tr in db.uspTranscripts(personId)
from a in db.PersonTranscripts.Where(x => x.UPID == personId)
from b in db.LU_CreditType.Where(x => x.ID == a.CreditTypeID)
select new CertViewModel
{
ActivityTitle = tr.ActivityTitle,
Score = tr.Score,
Status = tr.Status,
CompletionDate = tr.CompletionDate,
CretitTypeName = b.ShortName,
CompletedDateSorted = a.HK_CreatedOn
}).OrderByDescending(x => x.CompletedDateSorted).ToList();
List<CertViewModel> certlist = cert;
foreach (var item in certlist)
{
string itemWithoutHour = item.CompletionDate.Value.ToShortDateString();
var itemConverted = DateTime.ParseExact(itemWithoutHour, "M/d/yyyy", null);
item.CompletionDate = itemConverted;
}
return certificateslist.GroupBy(x => x.ActivityTitle).Select(e => e.First()).ToList();
}

For any given DateTime object, you can reference its Date property to strip out the time values:
var withTime = DateTime.Now; // 8/7/2016 22:11:43
var withoutTime = withTime.Date; // 8/7/2016 00:00:00

The .NET framework does not have a date-only object.
It may be worth understanding how the DateTime structure works. Internally, it stores an offset in ticks (1 tick = 100 nanoseconds) since 1/01/0001 12:00 am in a single 64-bit unsigned integer. (1 tick = 100 nanoseconds)
The DateTime structure then provides many useful methods and properties for dealing with dates and times, such as adding some days to an existing date, or calculating the difference of two times. One useful property is Date, which rounds a DateTime object down to the nearest day (12:00 am).
Dates, times and dates-with-times are all very similar, the main difference is how you format them, a date-with-time where you omit the time is just a date.
What David has suggested is that you work with the DateTime structure internally, strip any times using the Date property, sort on the DateTime, compare them and modify them as DateTime objects.
Only convert them to a string when they need to be displayed, at which point you can use methods such as ToShortDateString() or ToString(string format) to display only the date.

Convert dd/MM/yyyy to yyyy/MM/dd?

I want to convert a string '30/12/2012' to '2012/12/30'. My application is set to "en-CA" however the database accepts yyyy/MM/dd as default.
How can I do this without depending on the current culture info set
at server?

As all the comments have said, but none of the answers have said so far: don't pass this to the database as a string.
Parse any text you receive as early as possible, then use DateTime to represent it everywhere else, including how you send it to the database, via parameterized SQL1. This goes for values of all kinds: convert it into the "natural" type for the data as soon as possible, and keep it in that natural representation for as long as possible. A date isn't a string, and you should only convert it to a string if you really, really need to - ideally just before displaying it to a user.
The parsing can be done with DateTime.ParseExact or DateTime.TryParseExact depending on whether this is "suspicious" data (e.g. from a user) or data which should really be correct and for which an exception is the most appropriate reaction to unparseable values. I suggest you pass in CultureInfo.InvariantCulture with your custom format string. For example:
DateTime date = DateTime.ParseExact(text, "dd/MM/yyyy",
CultureInfo.InvariantCulture);
(If you do a lot of date/time work, you may also want to consider using my Noda Time project which allows you to express the value in a richer way - in this case you'd probably use LocalDate.)
1 If you're not already using parameterized SQL, but are instead baking values directly into the SQL, you have bigger problems than date/time conversions.

You can specify CultureInfo in Format and most ToString functions.
I.e. DateTime.ToString(CultureInfo) and DateTime.Parse(string, CultureInfo) will let you pars string in one culture (i.e. current or new CultureInfo("en-CA")) and format with another like new CultureInfo("en-us").
Note: you may consider running all DB access under some other culture (i.e. en-US) by setting Thread.CurrentCulture as sometimes number fomats are also impacted (if numbers are storead as string).

If its going to always be in the same format. Then split it on the / character
string[] tempsplit = datestring.Split('/');
and then put it back together
string joinstring = "/";
string newdate = tempsplit[2] + joinstring + tempsplit[1] + joinstring + tempsplit[0];
simple.

First convert your string to DateTime format using
DateTime dt = Convert.ToDateTime("your string value");
Then save it in string using:
string st=dt.ToString("yyyy/MM/dd");
This will convert your date format to any desired format you want without depending on culture

Without going into the issue what format the database accepts or not, you can do the conversion like this:
Convert the String to Datetime like explained here
Change the format and convert it to string again like this

This seems to work.
var x = new string[] { "2012/06/12", "20/06/2012", "111/111/1111" };
foreach (var ds in x)
{
DateTime d = default(DateTime);
try
{
d = DateTime.Parse(ds, CultureInfo.GetCultureInfo("en-CA"));
}
catch (Exception ex)
{
try
{
d = DateTime.ParseExact(ds, "yyyy/MM/dd", CultureInfo.InvariantCulture);
}
catch
{
}
}
if (d == default(DateTime))
Console.WriteLine("error");
else
Console.WriteLine(d.ToString());
}

.NET Date Add Days

I have date in this format "1999-05-31T13:20:00.000-05:00" I want to add some hours or days to it . Can some one suggest how to do that with this format and AddDays or AddHours ? Result need to return same format.

Try using DateTimeOffset.Parse. Then use AddDays or AddHours.
It is important to use DateTimeOffset instead of DateTime if you want to preserve the same timezone offset that you parsed.
var dateTimeOffset = DateTimeOffset.Parse("1999-05-31T13:20:00.000-05:00");
var newDateTimeOffset = dateTimeOffset.AddHours(1);
var newDateTimeString = newDateTimeOffset.ToString("O");
if you don't like the way "O" formats, you can use this:
var newDateTimeString = newDateTimeOffset.ToString("yyyy'-'MM'-'dd'T'HH':'mm':'ss'.'fffK")
This will 100% match to your format.

Example:
txt_del.Text = Calendar1.SelectedDate.ToString("MM/dd/yyyy");
/* for date picking textbox*/
double d2 = double.Parse(txt_till.Text);
/*second textbox for number of days to add*/
DateTime tom = Calendar1.SelectedDate.AddDays(d2);
/*for adding number of days to selected date*/
txt_total.Text = tom.ToString("MM/dd/yy")

Use DateTime.Parse(...) to create a DateTime object. Then you can add days and/or hours, and then ToString() to get the new string.

That looks like datetimeoffset. Perhaps from sql server? You should be able to use the datetimeoffset structure and the parse method. Once you have a datetimeoffset type you can use addhours or related methods.