I'm converting a small MSAccess application to a web-based ASP.NET app, using C# 3.5. I was wondering what's the best way to work with dates in C#, when converting some of this VBA code over to C#.
Here is an example of the VBA Code:
Coverage1=IIf(IsNull([EffDate1]),0,IIf([CurrDate]<=[EndDate1],[CurrDate]-[EffDate1],[EndDate1]-[EffDate1]+1))
Here is what my current C# code looks like with the errors denoted in the commented code:
public DateTime CalculateCoverageOne(DateTime dateEffDateOne, DateTime dateCurrentDate, DateTime dateEndDateOne)
{
if (dateCurrentDate.Date <= dateEndDateOne.Date)
{
return null; //Get "cannot convert null to System.DateTime because it is a non-nullable value type" error
}
else
{
if (dateCurrentDate.Date <= dateEndDateOne)
{
return dateCurrentDate.Subtract(dateEffDateOne); //Gets error "cannot implicitly convert system.timepsan to system.datetime
}
else
{
return dateEndDateOne.Subtract(dateEffDateOne.AddDays(1)); //Gets error "cannot implicitly convert system.timepsan to system.datetime
}
}
}
cannot convert null to System.DateTime because it is a non-nullable value type" error
The DateTime type is a value type, which means that it cannot hold a null value. To get around this you can do one of two things; either return DateTime.MinValue, and test for that when you want to use the value, or change the function to return DateTime? (note the question mark), which is a nullable DateTime. The nullable date can be used like this:
DateTime? nullable = DateTime.Now;
if (nullable.HasValue)
{
// do something with nullable.Value
}
cannot implicitly convert system.timepsan to system.datetime
When you subtract a DateTime from another DateTime, the result is a TimeSpan, representing the amount of time between them. The TimeSpan does not represent a specific point in time, but the span itself. In order to get the date, you can use the Add method or the Subtract method overload of a DateTime object that accepts a TimeSpan. Exactly how that should look I can't say, since I don't know what the different dates in your code represent.
In the last case, you can simply use the return value from the AddDays method, but with a negative value (in order to subtract one day, instead of adding one):
return dateEffDateOne.AddDays(-1);
It looks like your VB is actually returning a time span, presumably in days. Here's the closest direct translation:
public TimeSpan CalculateCoverageOne(DateTime EffDate1, DateTime CurrDate, DateTime? EndDate1)
{
return (EndDate1 == null) ? TimeSpan.Zero :
(CurrDate < EndDate1) ? (CurrDate - EffDate1) :
(EndDate1.AddDays(1) - EffDate1);
}
If instead you just wanted a count of days, just return the TimeSpan's Days property:
public int CalculateCoverageOne(DateTime EffDate1, DateTime CurrDate, DateTime? EndDate1)
{
return ((EndDate1 == null) ? TimeSpan.Zero :
(CurrDate < EndDate1) ? (CurrDate - EffDate1) :
(EndDate1.AddDays(1) - EffDate1)).Days;
}
And for good measure, this is how I would clean up your final version:
public int CalculateCoverageOne(DateTime dateCurrentDate, DateTime dateEffectiveDate, DateTime dateEffDateOne, DateTime dateEndDateOne)
{
TimeSpan ts;
if (dateEffDateOne == DateTime.MinValue)
{
ts = TimeSpan.Zero;
}
else if (dateEffectiveDate <= dateEndDateOne)
{
ts = dateCurrentDate - dateEffDateOne;
}
else
{
ts = (dateEndDateOne - dateEffDateOne) + new TimeSpan(1, 0, 0, 0);
}
return ts.Days;
}
Get the TimeSpan, then subtract that from the DateTime to get the date you want. For your inner IF statement, it would look like this:
TimeSpan estSpan = dateCurrentDate.Subtract(dateEffDateOne);
return dateCurrentDate.Subtract(estSpan);
EDIT: You may also want to return DateTime.MaxValue and have the calling function check for the max value, instead of returning null.
DateTime is a value type. So, you cannot assign null to DateTime.
But you can use a special value like DateTime.MinValue to indicate whatever you were trying to indicate by null.
DateTime represents a date (and time), like "July 22, 2009". This means, you shouldn't use this type to represent time interval, like, "9 days". TimeSpan is the type intended for this.
dateCurrentDate.Subtract(dateEffDateOne) (or, equivalently, dateCurrentDate-dateEffDateOne) is a difference between two dates, that is, time interval. So, I suggest you to change return type of your function to TimeSpan.
TimeSpan is also a value type, so you could use, for instance, TimeSpan.Zero instead of null.
After some excellent answers (I've up-voted you guys), I've finally hammered out what I think is my answer. Turns out that returning an int, as the number of days, is what worked for me in this situation.
Thanks everyone, for providing your awesome answers. It helped me get on the right track.
public int CalculateCoverageOne(DateTime dateCurrentDate, DateTime dateEffectiveDate, DateTime dateEffDateOne, DateTime dateEndDateOne)
{
//Coverage1=
//IIf(IsNull([EffDate1]),0,
//IIf([CurrDate]<=[EndDate1],
//[CurrDate]-[EffDate1],
//[EndDate1]-[EffDate1]+1))
if (dateEffDateOne.Equals(TimeSpan.Zero))
{
return (TimeSpan.Zero).Days;
}
else
{
if (dateEffectiveDate <= dateEndDateOne)
{
return (dateCurrentDate - dateEffDateOne).Days;
}
else
{
return (dateEndDateOne - dateEffDateOne).Add(new TimeSpan(1, 0, 0, 0)).Days;
}
}
}
Related
I'm trying to subtract short? Days from DateTime? InitialDate to get DateTime FinalDate.
I'm not sure if, because they are nullable objects, this is causing problems with the comparison. I've tried casting days to a TimeSpan without success.
short? Days = 7;
DateTime? InitialDate = new DateTime(2012, 10, 5);
DateTime FinalDate = InitialDate - Days ;
//FinalDate should be 5/3/2012 12:00 AM
FinalDate should be 5/3/2012 12:00 AM.
Since both the variables you are dealing with are nullable types, you have to make use of the .Value property of them to access its value. You can also make use of the .HasValue property to check whether it is having any value.
Now comes the subtraction part, I'm not sure what is the role of TimeSpan that you mentioned in the question. But from the output specified and the name of the variable, I assumed that its the number of days. If my understandings are correct, then you can try the following code to subtract the Days from InitialDate to get the FinalDate
For a safe side, you can check whether the InitialDate has a value or not before accessing them.
DateTime? FinalDate = InitialDate.HasValue ? InitialDate.Value.AddDays(-(Days.HasValue? Days.Value : 0)) : null;
This Example may help you to understand things more clear.
You can just subtract the Days value from the InitialDate using the AddDays method, passing in the negative value of Days. Since you don't show what you want to happen it either value is null I've made FinalDate nullable:
short? Days = 7;
DateTime? InitialDate = 5/10/2012 12:00 AM;
DateTime FinalDate? = null;
if(Days.HasValue && InitialDate.HasValue)
{
FinalDate = InitialDate.Value.AddDays(-Days.Value)
}
I am trying to convert string to DateTimeOffset.I am using DatetimeOffset.Parse(string).Parse obviously throws an exception when string is not in correct format.It is not able to parse 0000-00-00.
I want a single line of code saying me the best possible way to tackle this situation.If input is 0000-00-00 then it should be converted to current DateTimeOffset.
Any other string also apart from 0000-00-00 that cant be parsed should be changed to DateTimeOffset.Now.
If I understand your question correctly, you are looking for
DateTimeOffset dto = (input == "0000-00-00" ? DateTimeOffset.Now : DateTimeOffset.Parse(input));
EDIT
Based on your clarification that all invalid dates should default to the current time, the following will do that:
DateTimeOffset dto;
if(!DateTimeOffset.TryParse(input, out dto))
dto = DateTimeOffset.Now;
You can not change the logic of DateTimeOffset.Parse method. You can write a helper method which will check for the value "0000-00-00" and return current DateTimeOffset else try to parse the input value to DateTimeOffset and return respective value
public class DateTimeOffsetHelper
{
public static DateTimeOffset FromString(string offsetString)
{
DateTimeOffset offset;
if (!DateTimeOffset.TryParse(offsetString, out offset))
{
offset = DateTimeOffset.Now;
}
return offset;
}
}
And you can use it as following.
var offsetString = "2017-05-30";
var offset = DateTimeOffsetHelper.FromString(offsetString);
This should help you resolve you issue.
Here's a fairly simple one-liner.
Func<string, DateTimeOffset> parseDateTimeOffset = input =>
input == "0000-00-00" || DateTimeOffset.TryParse(input, out DateTimeOffset output)
? DateTimeOffset.Now
: output;
It is C#7 though.
i came across a situation that, i need to get only the Date out from DateTime.
i am having a DateTime? StartDate property (Nullable) used to hold the date value
i tried below,
var d = Convert.ToDateTime(StartDate).Date;
but its returning me d as eg. 6/22/2006 12:00:00AM
after doing var d = Convert.ToDateTime(StartDate).Date.ToString("d");
i'm able to get d as 6/22/2006..but i dont want to convert my DateTime? to String
is their any way to get only the Date without using the ToString("d")?
Use the Date property to get the Date component of DateTime instance:
DateTime dateTimeNow = DateTime.Now;
DateTime datePartOnly = dateTimeNow.Date; // Return 00/00/0000 00:00:00
With this approach, Date property will return the date at midnight. So the time part will be 00:00:00 in this case.
There are couple of alternate ways to get the just the Date part, but the return type of it will be a string:
1.) Using .ToString(string? format) where format can be standard or custom format string
string dateOnlyString = dateTimeNow.ToString("dd/MM/yyyy");
//Can also use .ToString("dd-MM-yyyy");
2.) Using .ToShortDateString() to return a culture sensitive date string
string dateOnlyString = dateTimeNow.ToShortDateString();
//Returns M/d/yyyy for "en-US" culture
//Returns yyyy/M/d for "ja-JP" culture
Reference: here.
try this:
string x = DateTime.Now.ToShortDateString().
this will get the date dd/mm/yy given to the string x.
I think you question is sort of... moot.
You ask for a date without a time, but get a DateTime, which has both. I really don't think that should be a problem in most cases though:
If you create a DateTime with a certain date, and compare it to another date, and both of these have their time set to midnight, your comparisons will be valid and correct. Eg:
var yesterday = new DateTime(2014, 3, 10);
var today = new DateTime(2014, 3, 11);
var tomorrow = new DateTime(2014, 3, 12);
Comparing and sorting these will work as you expect, and so will the following:
if(today == DateTime.Today){
Console.WriteLine("Today is the day!");
}
In other words, you should be perfectly fine just pretending like the time-part does not exist.
Also, as you touched upon yourself in the OP, you can use the property Date if you want to make sure to avoid any time-component:
// Note the addition of hours, minutes and seconds:
var today = new DateTime(2014, 3, 11, 14, 35, 33);
if(today == DateTime.Today){
Console.WriteLine("This never happened...");
}
if(today.Date == DateTime.Today){
Console.WriteLine("...But today is still the day!");
}
In C# 10 you can use DateOnly.
DateOnly date = DateOnly.FromDateTime(DateTime.Now);
A DateTime does have both a date and a time. You can decide with yourself that in a specific property you well never use the date part. It will just be 12:00 AM, but you won't use it.
In some situations it can be useful to write your own type that can never hold a time-of-day component. Here is a start:
struct Date : IFormattable
{
readonly DateTime value;
public Date(DateTime dateAndTime)
{
value = dateAndTime.Date;
}
public string ToString(string format, IFormatProvider formatProvider)
{
return value.ToString(format ?? "d", formatProvider);
}
public string ToString(string format)
{
return ToString(format, null);
}
public string ToString(IFormatProvider formatProvider)
{
return ToString(null, formatProvider);
}
public override string ToString()
{
return ToString(null, null);
}
public static implicit operator DateTime(Date date)
{
return date.value;
}
}
The field value does hold the 12 AM thing, but it is private and is not seen from the outside. The overloads of ToString() make sure that unless something else is requested, the Date is written out with the short date format of the current culture.
I'm trying to convert a string to datetime to validate if user input is actually a date.
The error I'm getting is:
Cannot implicitly convert type bool to System.DateTime.
I've been looking online for a while and can't find anything specific enough to help me understand.
Code:
public bool is21YearsOfAge(string argument)
{
DateTime _parsedDateArgument;
DateTime convertStringToDate = System.DateTime.TryParse(argument, out >_parsedDateArgument);
if (convertStringToDate > DateTime.Now)
{
//do something
}
}
Thanks in advance.
The TryParse method returns a bool that informs you whether the parse was successful, rather than throwing an exception like the Parse method does. Try doing this:
DateTime convertStringToDate;
bool isDate = DateTime.TryParse(argument, out convertStringToDate);
If argument is a date, convertStringToDate will contain that date as a DateTime.
DateTime.TryParse returns bool to indicate if parsing was successeful. So you should do
System.DateTime.TryParse(argument, out _parsedDateArgument);
DateTime convertStringToDate =_parsedDateArgument
Look at the documentation for DateTime.TryParse - it returns a bool, but has an out parameter for the parsed result:
DateTime dateTime;
bool success = DateTime.TryParse(text, out dateTime);
If success is false, that means the text couldn't be parsed. (So typically at this point you'd display an error to the user.)
You've already got the out parameter - why did you expect to end up with two different DateTime values (one as the return value and one from the out parameter)?
When you get an error like this, always read the documentation as the first step towards diagnosing the problem.
It should be
DateTime convertStringToDate;
if(System.DateTime.TryParse(argument, out convertStringToDate))
{
//Now you will have converted date in convertStringToDate
if (convertStringToDate > DateTime.Now)
{
//do something
}
}
else
{
//argument not have a valid date
}
System.DateTime.TryParse will retrun true if, argument will have a valid date string to convert. and the converted date will be store in its out parameter.
DateTime.TryParse do not return a DateTime value. It returns a bool indicating if it could parse it.
Instead use
DateTime convertStringToDate;
if(DateTime.TryParse(argument, out convertStringToDate)){
//ok value is good
}else{
//Not ok value is not good
}
use this instead,
DateTime _parsedDateArgument;
bool success = System.DateTime.TryParse(argument, out _parsedDateArgument);
Always remember that Tryparse always return boolean.
TryParse returns a bool, use just Parse instead, or assign the out variable to the new you have:
System.DateTime.TryParse(argument, out _parsedDateArgument);
DateTime convertStringToDate = _parsedDateArgument;
or like this:
DateTime convertStringToDate = DateTime.Parse(argument);
add the following namespace
using System.Globalization;
Create object of CultureInfo class
CultureInfo MyCI = new CultureInfo("en-US");
DateTime convertStringToDate = System.DateTime.TryParse(argument.ToString("MM/dd/yy", MyCI), out _parsedDateArgument);
I would declare an empty String variable like this:
string myString = string.Empty;
Is there an equivalent for a 'DateTime' variable ?
Update :
The problem is I use this 'DateTime' as a parameter for a 'StoredProcedure' in SQL.
E.g:
DateTime? someDate = null;
myCommand.Parameters.AddWithValue("#SurgeryDate", someDate);
When I run this code an exception is catched telling me the 'StoredProcedure' expected a '#SurgeryDate' parameter.
But i provided it.
Any idea why?
Since DateTime is a value type you cannot assign null to it, but exactly for these cases (absence of a value) Nullable<T> was introduced - use a nullable DateTime instead:
DateTime? myTime = null;
No. You have 2 options:
DateTime date = DateTime.MinValue;
This works when you need to do something every X amount of time (since you will always be over MinValue) but can actually cause subtle errors (such as using some operators w/o first checking if you are not MinValue) if you are not careful.
And you can use Nullable:
DateTime? date = null;
Which is nice and avoids most issues while introducing only 1 or 2.
It really depends on what you are trying to achieve.
You can set a DateTime variable to be '1/1/0001 00:00:00' but the variable itself cannot be null. To get this MinTime use:
DateTime variableName = DateTime.MinValue;
You may want to use a nullable datetime. Datetime? someDate = null;
You may find instances of people using DateTime.Max or DateTime.Min in such instances, but I highly doubt you want to do that. It leads to bugs with edge cases, code that's harder to read, etc.
The method you used (AddWithValue) doesn't convert null values to database nulls. You should use DBNull.Value instead:
myCommand.Parameters.AddWithValue(
"#SurgeryDate",
someDate == null ? DBNull.Value : (object)someDate
);
This will pass the someDate value if it is not null, or DBNull.Value otherwise. In this case correct value will be passed to the database.
Either:
DateTime dt = new DateTime();
or
DateTime dt = default(DateTime);
If you set the date to
DateTime dNewDate = new DateTime();
The value is set to {1/1/0001 12:00:00 AM}
Option 1: Use a nullable DateTime?
Option 2: Use DateTime.MinValue
Personally, I'd prefer option 1.
A string is a sequence of characters. So it makes sense to have an empty string, which is just an empty sequence of characters.
But DateTime is just a single value, so it's doesn't make sense to talk about an “empty” DateTime.
If you want to represent the concept of “no value”, that's represented as null in .Net. And if you want to use that with value types, you need to explicitly make them nullable. That means either using Nullable<DateTime>, or the equivalent DateTime?.
DateTime (just like all value types) also has a default value, that's assigned to uninitialized fields and you can also get it by new DateTime() or default(DateTime). But you probably don't want to use it, since it represents valid date: 1.1.0001 0:00:00.
There's no such thing as an empty date per se, do you mean something like:
DateTime? myDateTime = null;
The .addwithvalue needs dbnull.
You could do something like this:
DateTime? someDate = null;
//...
if (someDate == null)
myCommand.Parameters.AddWithValue("#SurgeryDate", DBnull.value);
or use a method extension...
public static class Extensions
{
public static SqlParameter AddWithNullValue(this SqlParameterCollection collection, string parameterName, object value)
{
if (value == null)
return collection.AddWithValue(parameterName, DBNull.Value);
else
return collection.AddWithValue(parameterName, value);
}
}
This will work for null able dateTime parameter
. .
SearchUsingDate(DateTime? StartDate, DateTime? EndDate){
DateTime LastDate;
if (EndDate != null)
{
LastDate = (DateTime)EndDate;
LastDate = LastDate.AddDays(1);
EndDate = LastDate;
}
}