Here's my code:
DateTime date1 = new DateTime(byear, bmonth, bday, 0, 0, 0);
DateTime datenow = DateTime.Now;
DateTime date2 = datenow - date1
On the last line I am getting this error:
Error 1 Cannot implicitly convert type 'System.TimeSpan' to 'System.DateTime'
How do I subtract two dates?
Well the point is that if you think of it, subtracting a date to another should not yield a date, it should yield a time span. And that is what happens when you use DateTime.Subtract().
TimeSpan timeSpan = datenow - date1; //timespan between `datenow` and `date1`
This will make your current code work.
If on the other hand you want to subtract, let's say, one year from your date, you can use:
DateTime oneYearBefore = DateTime.Now.AddYears(-1); //that is, subtracts one year
As already mentioned, date - date gives you a TimeSpan, not a DateTime. If you want a DateTime, use AddDays(-1) as in:
DateTime subtractedDate = date1.AddDays(-1);
The result of a date comparison is a TimeSpan, not a DateTime value.
You want to do this:
TimeSpan result = datenow - date1;
.Subtract has two overloads. One accepts a DateTime and returns a TimeSpan, the other accepts a TimeSpan and returns a DateTime.
In other words, if you subtract a date from a date, you get the timespan difference. Otherwise, if you subtract a timespan from a date, you get a new date.
Can you clarify what you are trying calculate? The difference between any two dates in C# or real life is a time span. If you are trying to calculate age then what you want is the timespan since their birth. Change Date2 to to
Timespan age = datenow - date1;
You are correctly subtracting two dates in your code. What's going on is that you expect the difference between the two dates to be another date, and that's not the case.
As other posters have noticed, you get a TimeSpan. From your variable names I get the sense you're trying to find out someone's age.
Age is not a date, it's a duration. Read up on the TimeSpan object and you will find that it correctly expresses the idea you are looking for.
I'm not 0029-01-01 years old, I'm 29 years old. (Today is not my birthday, but assume it is for easy math.)
If you're trying to show someone's age in a control and that control wants a DateTime you are probably using the wrong control to do it.
Try using ticks...?
DateTime date1 = new DateTime(1986, 3, 16, 0, 0, 0);
DateTime datenow = DateTime.Now;
DateTime date2 = new DateTime(datenow.Subtract(date1).Ticks);
You are expecting the difference of two dates to be a date which is not. That being said, if you need to subtract a certain number of days or months, it can easily be done using the built in methods of the DateTime object such as .AddDays(-1), note that I used a negative number to substract, you can apply the opposite. Here is a quick example.
DateTime now = DateTime.Now;
// Get the date 7 days ago
DateTime sevenDaysAgo = now.AddDays(-7);
// Bulk: Get the date 7 days and two hours ago
DateTime sevenDaysAndtwoHoursAgo = now.Add(-(new TimeSpan(7, 2, 0, 0)));
Use this code:
DateTime? Startdate = cStartDate.GetValue<DateTime>().Date;
DateTime? Enddate = cEndDate.GetValue<DateTime>().Date;
TimeSpan diff = Enddate.GetValue<DateTime>()- Startdate.GetValue<DateTime>() ;
txtDayNo.Text = diff.Days.GetValue<string>();
TimeSpan Example:
private void Form1_Load(object sender, EventArgs e)
{
DateTime startdatetime = new DateTime(2001, 1, 2, 14, 30, 0);
DateTime enddatetime = DateTime.Now;
TimeSpan difference = enddatetime.Subtract(startdatetime);
string sdifference = "TotalDays:" + difference.TotalDays + Environment.NewLine;
sdifference += "TotalHours:" + difference.TotalHours + Environment.NewLine;
sdifference += "TotalMilliseconds:" + difference.TotalMilliseconds + Environment.NewLine;
sdifference += "TotalMinutes:" + difference.TotalMinutes + Environment.NewLine;
sdifference += "TotalSeconds:" + difference.TotalSeconds + Environment.NewLine;
sdifference += "Ticks:" + difference.Ticks + Environment.NewLine;
sdifference += "Total:" + difference.Days + " days, " + difference.Hours + " hours, " + difference.Minutes + " minutes, " + difference.Seconds + " seconds and " + difference.Milliseconds + " milliseconds.";
TextBox TextBox1 = new TextBox();
TextBox1.Multiline = true;
TextBox1.Dock = DockStyle.Fill;
TextBox1.Text = sdifference;
this.Controls.Add(TextBox1);
}
Not exactly an answer to your question, but I prefer using var instead of annotating the variables with types. var IMO makes code look much cleaner than otherwise.
Here's your code snippet with vars:
var date1 = new DateTime(byear, bmonth, bday, 0, 0, 0);
var datenow = DateTime.Now;
var date2 = datenow - date1;
EDIT:
For the C# developers with the var-is-bad mindset:
[ Original Post Here ]
I use var extensively. There has been
criticism that this diminishes the
readability of the code, but no
argument to support that claim.
Admittedly, it may mean that it's not
clear what type we are dealing with.
So what? This is actually the point of
a decoupled design. When dealing with
interfaces, you are emphatically not
interested in the type a variable has.
var takes this much further, true, but
I think that the argument remains the
same from a readability point of view:
The programmer shouldn't actually be
interested in the type of the variable
but rather in what a variable does.
This is why Microsoft also calls type
inference “duck typing.”
So, what does a variable do when I
declare it using var? Easy, it does
whatever IntelliSense tells me it
does. Any reasoning about C# that
ignores the IDE falls short of
reality. In practice, every C# code is
programmed in an IDE that supports
IntelliSense.
If I am using a var declared variable
and get confused what the variable is
there for, there's something
fundamentally wrong with my code. var
is not the cause, it only makes the
symptoms visible. Don't blame the
messenger.
Now, the C# team has released a coding
guideline stating that var should only
be used to capture the result of a
LINQ statement that creates an
anonymous type (because here, we have
no real alternative to var). Well,
screw that. As long as the C# team
doesn't give me a sound argument for
this guideline, I am going to ignore
it because in my professional and
personal opinion, it's pure baloney.
(Sorry; I've got no link to the
guideline in question.)
Actually, there are some
(superficially) good explanations on
why you shouldn't use var but I still
believe they are largely wrong. Take
the example of “searchabililty”: the
author claims that var makes it hard
to search for places where MyType is
used. Right. So do interfaces.
Actually, why would I want to know
where the class is used? I might be
more interested in where it is
instantiated and this will still be
searchable because somewhere its
constructor has to be invoked (even if
this is done indirectly, the type name
has to be mentioned somewhere). -
Konrad Rudolph
Related
Using C#, I am trying to populate a variable with a known filename + date. The catch is that the date must always be the last day of the previous month. It must also have no slashes or hyphens, and the year must be two digits. For example, if it is now November 27 2015, I need my filename to be: Foobar_103115.txt
As a programmer who still has much to learn, I have written the clunky code below and it does achieve my desired result, even though it will obviously break after the end of this century. My code is written this way because I could not figure out a more direct syntax for getting the date I want, complete with the specified formatting.
My question is this: What would be a more elegant and efficient way of recreating the below code?
I have commented all the code for any novice programmers who might be interested in this. I know the experts I'm asking for help from don't need it.
public void Main()
{
String Filename
DateTime date = DateTime.Today;
var FirstDayOfThisMonth = DateTime.Today.AddDays(-(DateTime.Today.Day - 1)); //Gets the FIRST DAY of each month
var LastDayOfLastMonth = FirstDayOfThisMonth.AddDays(-1); //Subtracts one day from the first day of each month to give you the last day of the previous month
String outputDate = LastDayOfLastMonth.ToShortDateString(); //Reformats a long date string to a shorter one like 01/01/2015
var NewDate = outputDate.Replace("20", ""); //Gives me a two-digit year which will work until the end of the century
var NewDate2 = NewDate.Replace("/", ""); //Replaces the slashes with nothing so the format looks this way: 103115 (instead of 10/31/15)
Filename = "Foobar_" + NewDate2 + ".txt"; //concatenates my newly formatted date to the filename and assigns to the variable
Sounds like you want something more like:
// Warning: you should think about time zones...
DateTime today = DateTime.Today;
DateTime startOfMonth = new DateTime(today.Year, today.Month, 1);
DateTime endOfPreviousMonth = startOfMonth.AddDays(-1);
string filename = string.Format(CultureInfo.InvariantCulture,
"FooBar_{0:MMddyy}.txt", endOfPreviousMonth);
I definitely wouldn't use ToShortDateString here - you want a very specific format, so express it specifically. The results of ToShortDateString will vary based on the current thread's culture.
Also note how my code only evaluates DateTime.Today once - this is a good habit to get into, as otherwise if the clock "ticks" into the next day between two evaluations of DateTime.Today, your original code could give some pretty odd results.
I am working on a new project in c#, i have no experience with date and time.
Here i need to find the difference between two time values which is in string format
string pointavalue = comboBox1.Text + ":" + comboBox2.Text + ":" + comboBox5.Text;
string pointbvalue = comboBox3.Text + ":" + comboBox4.Text + ":" + comboBox6.Text;
string pointcvalue = comboBox7.Text + ":" + comboBox8.Text + ":" + comboBox9.Text;
DateTime pointa = DateTime.Parse(pointavalue, System.Globalization.CultureInfo.CurrentCulture);
DateTime pointb = DateTime.Parse(pointbvalue, System.Globalization.CultureInfo.CurrentCulture);
DateTime pointc = DateTime.Parse(pointcvalue, System.Globalization.CultureInfo.CurrentCulture);
string time1 = pointa.ToString("HH:mm:ss");
string time2 = pointb.ToString("HH:mm:ss");
string time3 = pointc.ToString("HH:mm:ss");
There is three Values pointavalue, pointbvalue. pointcvalue.
They are combined string values of comboboxes.
Now how do i subtract pointbvalues from pointavalues?
I know they are in string format so operations cannot be performed.
the code you are looking is not mine, someone helped me but its working as a expected.
I am learning C# so bear with me.
ok i think figure out something, but still i can't solve it.
Here is my recent work with the code
DateTime inputa = DateTime.Parse(label21.Text, System.Globalization.CultureInfo.CurrentCulture);
DateTime inputb = DateTime.Parse(label23.Text, System.Globalization.CultureInfo.CurrentCulture);
if (pointa < pointb)
{
TimeSpan diff1 = pointb.Subtract(pointa);
DateTime d1=Convert.ToDateTime(diff1);
if (d1 < inputa)
{
label34.Text = "fail";
}
else
{
label34.Text = "pass";
}
Here i want to check the condition of the time diff1 and inputa, that's it that's all i need to finish this project.
The reason why you can't solve this problem is that you are trying to compare two different data types, Timespan and Datetime are not same
Either convert all your string to "Timespan" (That is better option).
Datetime will give you the present date, but it seems you don't need that.
Last but not least learn some basics before you ask these questions.
One more simple example:
void Main()
{
DateTime now = DateTime.Now;
DateTime yesterday = now.AddDays(-1);
TimeSpan difference = yesterday - now;
Console.WriteLine (difference.GetType().Name);
Console.WriteLine (difference.TotalSeconds); // expecting -86400
}
running this will print
TimeSpan
-86400
Take a look at the DateTime.Substract method:
TimeSpan abdiff = pointb.Substract(pointa);
TimeSpan bcdiff = pointc.Substract(pointb);
Alternatively, you can use the - operator, you get back a Timespan which contains the differences:
TimeSpan abdiff = pointb - pointa;
TimeSpan bcdiff = pointc - pointb;
Assuming that your combo boxes contain the hour, minute, and second then you could do the following.
TimeSpan pointa = new TimeSpan(int.Parse(comboBox1.Text), int.Parse(comboBox2.Text), int.Parse(comboBox5.Text));
TimeSpan pointb = new TimeSpan(int.Parse(comboBox3.Text), int.Parse(comboBox4.Text), int.Parse(comboBox6.Text));
TimeSpan pointc = new TimeSpan(int.Parse(comboBox7.Text), int.Parse(comboBox8.Text), int.Parse(comboBox9.Text));
TimeSpan aTob = pointa > pointb
? pointa - pointb
: (pointa + TimeSpan.FromDays(1)) - pointb;
Basically this assumes that your combo boxes only have valid hour (0-23), minute (0-59), and second (0-59) values. Then you just need to determine if your times are on the same day or not. If you assume that pointa is latter than pointb then checking if it is greater than pointb means you can do a straight subtraction. If not then it must be the time for the next day and you just add 1 day to it before subtracting pointb.
This is based on your assertion that 01:00 - 23:00 should be 2 hours and not -22. Thought it would be best if there where a date included so you would know for sure if the times are on the same day or the next day or from completely different years.
I want to convert a Timespan to Datetime. How can I do this?
I found one method on Google:
DateTime dt;
TimeSpan ts="XXX";
//We can covnert 'ts' to 'dt' like this:
dt= Convert.ToDateTime(ts.ToString());
Is there any other way to do this?
It is not very logical to convert TimeSpan to DateTime. Try to understand what leppie said above. TimeSpan is a duration say 6 Days 5 Hours 40 minutes. It is not a Date. If I say 6 Days; Can you deduce a Date from it? The answer is NO unless you have a REFERENCE Date.
So if you want to convert TimeSpan to DateTime you need a reference date. 6 Days & 5 Hours from when? So you can write something like this:
DateTime dt = new DateTime(2012, 01, 01);
TimeSpan ts = new TimeSpan(1, 0, 0, 0, 0);
dt = dt + ts;
While the selected answer is strictly correct, I believe I understand what the OP is trying to get at here as I had a similar issue.
I had a TimeSpan which I wished to display in a grid control (as just hh:mm) but the grid didn't appear to understand TimeSpan, only DateTime . The OP has a similar scenario where only the TimeSpan is the relevant part but didn't consider the necessity of adding the DateTime reference point.
So, as indicated above, I simply added DateTime.MinValue (though any date will do) which is subsequently ignored by the grid when it renders the timespan as a time portion of the resulting date.
TimeSpan can be added to a fresh DateTime to achieve this.
TimeSpan ts="XXX";
DateTime dt = new DateTime() + ts;
But as mentioned before, it is not strictly logical without a valid start date. I have encountered
a use-case where i required only the time aspect. will work fine as long as the logic is correct.
You need a reference date for this to be useful.
An example from
http://msdn.microsoft.com/en-us/library/system.datetime.add.aspx
// Calculate what day of the week is 36 days from this instant.
System.DateTime today = System.DateTime.Now;
System.TimeSpan duration = new System.TimeSpan(36, 0, 0, 0);
System.DateTime answer = today.Add(duration);
System.Console.WriteLine("{0:dddd}", answer);
Worked for me.
var StartTime = new DateTime(item.StartTime.Ticks);
If you only need to show time value in a datagrid or label similar, best way is convert directly time in datetime datatype.
SELECT CONVERT(datetime,myTimeField) as myTimeField FROM Table1
You could also use DateTime.FromFileTime(finishTime) where finishTme is a long containing the ticks of a time. Or FromFileTimeUtc.
An easy method, use ticks:
new DateTime((DateTime.Now - DateTime.Now.AddHours(-1.55)).Ticks).ToString("HH:mm:ss:fff")
This function will give you a date (Without Day / Month / Year)
A problem with all of the above is that the conversion returns the incorrect number of days as specified in the TimeSpan.
Using the above, the below returns 3 and not 2.
Ideas on how to preserve the 2 days in the TimeSpan arguments and return them as the DateTime day?
public void should_return_totaldays()
{
_ts = new TimeSpan(2, 1, 30, 10);
var format = "dd";
var returnedVal = _ts.ToString(format);
Assert.That(returnedVal, Is.EqualTo("2")); //returns 3 not 2
}
First, convert the timespan to a string, then to DateTime, then back to a string:
Convert.ToDateTime(timespan.SelectedTime.ToString()).ToShortTimeString();
I want to compare between two dates.
From both the dates, I am fetching only date component using ToShortDateString(), as shown below. Now the problem is when I'm comparing the two dates. Its throwing error --
"Operator >= can't be applied to operands of type string and string."
DateTime srtdate = Convert.ToDateTime(allitem["StartDate"].Text.ToString());
DateTime srtdate = Convert.ToDateTime(allitem["StartDate"].Text.ToString());
(DateTime.Now.ToShortDateString() >= srtdate.ToShortDateString())
I need to compare date component only, NOT date and time together.
Please suggest what is the alternative way. Thanks
To JON:-
(I went tyhrough all what you explained and understood hopefully what the point actually you trying to make. Just to clarify more and make a last check I ll show an example.)
I have an web interface, where I give a start date and end date for a XYZ name (Note I can enter only date here, not time).
Start Date - 22-Feb-2012 AND End Date - 22-Feb-2012
Now in back end (code), if Start date and End date is same as Current date OR current date is in between start and end date, I want a ACTIVE flag set or else not. I give the condition as this:-
if ((DateTime.Today >= strdate.Date) && (DateTime.Today <= enddate.Date))
lblCondition.Text = "CHECKED";
Now when I debug the code,
Both DateTime.Today and strdate.Date gives the value as 2/22/2012 12:00:00 AM.
So, Jon my question is:- Would 'today' and 'date' work as per mentioned requirement, where only date component used. I hope it would.
Thanks a lot for all your explanantion before.
Why are you converting to a string representation at all? If you only want to compare the date parts to two DateTime values, just use the Date property on each of them:
if (x.Date >= y.Date)
And the Today property is equivalent to DateTime.Now.Date.
Both Date and Today strip off the time part, leaving a time of midnight. It's not ideal that you've still got a type which is capable of representing times, but that's just the way the DateTime API works :(
Note that you should usually avoid using DateTime.Now or DateTime.Today in web applications unless you're really comfortable with it using the system default time zone as the day boundary. The user's idea of "today" may not be the same as the server's.
You should avoid using string conversions unless your goal is really to get a text representation.
Of course another alternative would be to use the date/time library I'm building, Noda Time, where you could use a LocalDate type - obviously that makes it clearer that you're only interested in the date and not the time.
EDIT: As the OP seems unconvinced that Date really does ignore the time component, here's an example:
using System;
public class Test
{
static void Main()
{
// Two DateTime values with different times but
// on the same date
DateTime early = new DateTime(2012, 2, 22, 6, 0, 0);
DateTime late = new DateTime(2012, 2, 22, 18, 0, 0);
Console.WriteLine(early == late); // False
Console.WriteLine(early.Date == late.Date); // True
}
}
DateTime.Today >= strdate.Date
some thoughts
Think at the the following example: you need to compare the following numbers 1.5 and 2.5. These are represented in .Net as decimal, double or float, but let's use decimal. The greater one is 2.5
Let's say you need to compare the integral part of these numbers (1. and 2.). You will still use the decimal type to do the comparison.
Math.Truncate(x) ? Math.Truncate(y) // x = 1.5, y = 2.5
Same as for the DateTime. DateTime.Date will return the "integral" part of your date as Math.Truncate returns the integral part of a "real" number, but both will base on their original type.
hope this helps you.
using System;
public class Example
{
public static void Main()
{
DateTime date1 = new DateTime(2009, 8, 1, 0, 0, 0);
DateTime date2 = new DateTime(2009, 8, 1, 12, 0, 0);
int result = DateTime.Compare(date1, date2);
string relationship;
if (result < 0)
relationship = "is earlier than";
else if (result == 0)
relationship = "is the same time as";
else
relationship = "is later than";
Console.WriteLine("{0} {1} {2}", date1, relationship, date2);
}
}
// The example displays the following output:
// 8/1/2009 12:00:00 AM is earlier than 8/1/2009 12:00:00 PM
Suppose a time stamp (just time or date and time) where the time can roll over to the next day:
00:00:00 <- midnight
01:00:00 <- 1 AM
23:00:00 <- 11 PM
24:00:00 <- midnight, day + 1
25:00:00 <- 1 AM, day + 1
What would be a way to parse it easily into a C# DateTime that would perform the carry-over to the next day? In other words, "01:00:00" would become "0001-01-01 01:00:00" and "25:00:00" would become "0001-01-02 01:00:00".
EDIT:
I should mention that this fails miserably (i.e FormatException):
DateTime.ParseExact("0001-01-01 25:00:00", "yyyy-MM-dd HH:mm:ss", CultureInfo.InvariantCulture);
Since you're trying to represent a period of time from an arbitrary point, rather than as a specific date, perhaps you would be better off using the System.TimeSpan class? This allows you to set values of more than 24 hours in the constructor, and can be used with DateTime objects like this:
System.TimeSpan timestamp = new System.TimeSpan(25, 0, 0);
System.DateTime parsedDateTime = new DateTime(0, 0, 0);
parsedDateTime = parsedDateTime.Add(timestamp);
Console.WriteLine(parsedDateTime.ToString("yyyy-MM-dd HH:mm:ss")); //Output as "0001-01-02 01:00:00"
NOTE: Code is untested.
EDIT: In terms of parsing the strings, I can't think of any basic .NET objects that parse strings with values greater than 23 for the hour (since 25 is an invalid hour of the day), but assuming that the format is consistent, you could create a very simple string parsing routine (or even a regular expression) to read the values individually, and load the constructor manually.
If you have an existing DateTime value you can add to, you can always use a TimeSpan:
string dt = "25:00:00";
int hours = int.Parse(dt.Split(':')[0]);
TimeSpan ts = TimeSpan.FromHours(hours);
TimeSpan.Parse() doesn't work directly in this case because it complains (fair enough!) about the 25 in the hour notation.
If you want to code it out... this should be a starting point:
string dateString = "0001-01-01 25:00:00";
string[] parts = dateString.Split(' '); //now have '0001-01-01' and '25:00:00'
string datePart = parts[0]; // '0001-01-01'
string[] timeParts = parts[1].Split(':'); //now have '25', '00', and '00
DateTime initialDate = DateTime.ParseExact(datePart, "yyyy-MM-dd", CultureInfo.InvariantCulture);//use the date as a starting point
//use the add methods to get your desired datetime
int hours = int.Parse(timeParts[0]);
int minutes = int.Parse(timeParts[1]);
int seconds = int.Parse(timeParts[2]);
DateTime resultDate = initialDate.AddHours(hours)
.AddMinutes(minutes)
.AddSeconds(seconds);
Of course, it makes assumptions that the input is formatted properly and is parsable, etc..
In addition, you could definitely use timespan instead of the individual add methods for hour, minute, second as some other answers are..
In case nobody points out an out-of-the-box answer, here is a neat ActionScript class I wrote to parse time inputs (human input)...
https://github.com/appcove/AppStruct/blob/master/Flex/AppStruct/src/AppStruct/TimeInput.as
It would be very simple to port this to C#, and you could tweak the 24 hour logic to result in #days, #hours, #minutes.
Good luck!
You are specifying an invalid date. So not only can you not parse it, you cannot store it!
How about a nice TimeSpan object instead? (It also has a Parse() method.)
Alternatively, use a sscanf()-type function like the one at http://www.blackbeltcoder.com/Articles/strings/a-sscanf-replacement-for-net to extract each number separate. (Best if you have no control over the string format being read.)