Is it possible to create a C# pointer to a DateTime object? I'm trying to do this:
DateTime Event1 = DateTime.Now;
DateTime Event2 = DateTime.Now.AddYears(10);
DateTime EventPointer; // A Pointer?
if (something)
{
EventPointer = Event1;
}
else
{
EventPointer = Event2;
}
EventPointer.DoSomething? // Something that would change the value of Event1/2 variable.
Not directly, but you can wrap it around a class:
Wrapper w1 = new Wrapper { TheDate = DateTime.Now };
Wrapper w2 = new Wrapper { TheDate = DateTime.Now.AddYears(10) };
Wrapper w;
if (something)
{
w = w1;
}
else
{
w = w2;
}
w.DoSomething();
class Wrapper
{
public DateTime TheDate { get; set; }
public void DoSomething()
{
}
}
DateTimes are value types which unlike reference types everytime you assign its value to another variable their value is copied.
A DateTime is a value type, when you assign it the value is copied. However, methods can take a reference to a value type using the ref keyword. Your EventPointer.DoSomething would take a DateTime as reference. Here's a simple example of how you might be able to apply it.
var date = DateTime.Today;
MakeMinValue(ref date);
Console.Out.WriteLine("date = {0}", date);
public void MakeMinValue(ref DateTime dateTime)
{
dateTime = DateTime.MinValue;
}
This will only work with a method parameter.
You can't use pointers in managed code unless you use unsafe. I'd advise against it.
DateTimes are immutable. The only thing you can do to modify a variable of type DateTime is to reassign to it.
You can do something close to what you want, but in general it's not a good idea to do this:
DateTime event1 = new DateTime(2011, 10, 11);
DateTime event2 = new DateTime(2021, 10, 11);
Action<DateTime> eventPointer; // A Pointer?
if (true)
{
eventPointer = x => { event1 = x; };
}
else
{
eventPointer = x => { event2 = x; };
}
eventPointer(new DateTime(2016, 10, 11));
Console.WriteLine(event1.ToString(CultureInfo.InvariantCulture));
Console.WriteLine(event2.ToString(CultureInfo.InvariantCulture));
Result:
10/11/2016 00:00:00
10/11/2021 00:00:00
I think it is a better idea is to find another way to solve your problem.
Pointers, as you are thinking of them, don't exist in managed C# code. You might want to look into out and ref parameters if you need to pass a DateTime and have the original value change. Since DateTimes are structs (value type) they are always copied instead of passed by reference, unless you specifically use an out or ref parameter.
You can replace type of EventPointer, Event1 and Event2 types from DateTime type to DateTime?. It makes EventPointer's type nullable reference type.
DateTime? Event1 = DateTime.Now;
DateTime? Event2 = DateTime.Now.AddYears(10);
DateTime? EventPointer;
if (condition)
{
EventPointer = Event1;
}
else
{
EventPointer = Event2;
}
EventPointer.Value //.DoSomething
Related
I am trying to pull a date from a separate program and use it to determine the expiration dates of contracts. I have called int's for the month day and year and then used DateTime to assign to another var.
I am fairly new to C# and and can't find a work around for the error I get with this block. The errors tell me that it cannot implicitly convert int? to int, when I use an int? var to declare the day month and year it then shifts the error down to the DateTime line.
This probably needs to be structured differently but I can't figure out what that way would be.
private Instrument m_instr = null;
private void m_getInstrDetails(Instrument instr)
{
m_ContractName = instr.Name.ToString();
m_type = instr.Product.Type.ToString();
m_prod = instr.Product.ToString();
m_SmallestTickIncrtement = instr.InstrumentDetails.SmallestTickIncrement;
//month calc
int month = m_instr.InstrumentDetails.ExpirationDate.Month;
int day = m_instr.InstrumentDetails.ExpirationDate.Day;
int year = m_instr.InstrumentDetails.ExpirationDate.Year;
m_expDate1 = new DateTime(year, month, day);
A nullable integer (int?) cannot be cast to a traditional integer (int) since there are scenarios where one might be null, and you'll need to determine how you want to handle such occasions.
Consider Parsing or Using a Default Value
You need to determine what you want to occur when your nullable value is null. Nullable integers by default expose a HasValue property, which you can use to determine as a default or you could consider using the null-propagation operator to handle this :
// This will use the expiration date if it exists, otherwise it will use 1
int month = m_instr.InstrumentDetails.ExpirationDate?.Month ?? 1;
Another option involves setting an initial value and using the int.TryParse() method to update the value prior to use :
int month = 1;
int.TryParse(m_instr.InstrumentDetails.ExpirationDate?.Month, out month);
Considering Throwing an Exception
If you don't want to allow these types of scenarios to occur and using some default value isn't feasible, you could consider just throwing an exception :
if(!month.HasValue) { throw ArgumentException("month"); }
You can allow this to bubble up to the appropriate location and handle it accordingly within your application (i.e. notify the user, log the problem, etc.)
int? is a Nullable-type, that means, that your int also could be null.
You get the value by
int? month = m_instr.InstrumentDetails.ExpirationDate.Month;
int month = month.Value;
you could check, if month is not null by
bool monthIsNotNull = month.HasValue;
because you could get an exception when trying to initialize the DateTime-variable when month is null - or at least, when trying to get int via month.Value and month is null
the DateTime-constructor wants DateTime(int year, int month, int day) - he doesn't want to get e.g. a month that's null
Assuming that the ExpirationDate.<properties> are your int? s, if the concern is whether or not there is an ExpirationDate, shouldn't you see if that is null instead? Then you could just use regular ints as properties of an ExpirationDate object.:
private void m_getInstrDetails(Instrument instr)
{
m_ContractName = instr.Name.ToString();
m_type = instr.Product.Type.ToString();
m_prod = instr.Product.ToString();
m_SmallestTickIncrtement = instr.InstrumentDetails.SmallestTickIncrement;
if(InstrumentDetails.ExpirationDate != null)
{
//if you change the .Month, .Day, and .Year to int, and test against
//ExpirationDate, this will work fine
//month calc
int month = m_instr.InstrumentDetails.ExpirationDate.Month;
int day = m_instr.InstrumentDetails.ExpirationDate.Day;
int year = m_instr.InstrumentDetails.ExpirationDate.Year;
m_expDate1 = new DateTime(year, month, day);
}
}
I've got objects like:
DateTime a;
DateTime b;
DateTime c;
If I make:
b=a;
and then:
b=c;
my a equals c.
I understand that this are dynamic objects and I've binded them with reference. But I don't want to bind them. How can I avoid this? How can I make:b=c;without making a=c; in the same time?
DateTime is a struct which means it's a value type.
See the following example:
void Main()
{
DateTime a = new DateTime(2005, 05, 05);
DateTime b = a;
Console.WriteLine (a);
Console.WriteLine (b);
a = new DateTime(2012, 05, 05);
Console.WriteLine (a);
Console.WriteLine (b);
}
output:
5/05/2005 0:00:00
5/05/2005 0:00:00
5/05/2012 0:00:00
5/05/2005 0:00:00
Usually this can be done (in a different situation) by implementing ICloneable which defines the Clone method.
We are trying to override the DateTime.MinValue in our application, but by doing it we noticed that our Web services are timing-out, following is a sample code. Not sure what is wrong/what we are missing.
public MainWindow()
{
//Introducing this.. Causes timeout of the webservice call...
typeof(DateTime).GetField("MinValue").SetValue(typeof(DateTime),new DateTime(1900, 1, 1));
var yesitworks= DateTime.MinValue;
InitializeComponent();
ServiceReference1.Service1Client client = new ServiceReference1.Service1Client();
//Below call will timeout...
var value =client.GetData(10);
}
PS: This might not be the best solution for what we are trying resolve but now its more of curiosity as to why it is not working? how is it related.
DateTime.MinValue is a static readonly field. That means that library authors will not expect it to change, and may write code that depends on it having the expected value.
Hence, you should not change the value of DateTime.MinValue.
For example, a library may use it as the default value for a variable:
private mostRecentDate= DateTime.MinValue;
foreach (var date in myDates)
{
if (date > mostRecentDate)
{
mostRecentDate= date;
}
}
// Do something with the most recent date in myDates...
In this example, if myDates only contained dates earlier than your new value for DateTime.MinValue, then this code would set mostRecentDate to DateTime.MinValue rather than the latest date in myDates.
While this rather contrived example may not be good programming practise (for example, you could use Nullable instead), it is valid code, whose behaviour would be changed if you changed the value of DateTime.MinValue.
The point is that libraries you are using could also be dependant on the value on DateTime.MinValue, so changing it could break them. You are llucky in so far as you found out that this introduced a bug early. If you are unlucky, you would not see a problem until your software had gone live and some corner case was hit.
I had a similar problem recently.
You didn't tell why you wanted to override DateTime.MinValue, but I guess the reason is similar to mine:
I have a server written in .NET, which has .NET clients and (via COM-Interop) MS Access clients.
The clients pass DateTime values, and the server needs to check whether they passed a "real" value or DateTime.MinValue.
My problem was:
.NET's DateTime.MinValue is January 1st of the year 1
The smallest possible value for VBA's Date type is January 1st of the year 100
⇒ Checking for DateTime.MinValue didn't work when the data was coming from MS Access, because Date variables in Access can't hold a date as small as .NET's DateTime.MinValue.
At that point I tried to override DateTime.MinValue too, and found out it doesn't work.
My solution was to write an extension method for DateTime:
public static class DateTimeExtensions
{
public static bool MinValue(this DateTime input)
{
// check the min values of .NET *and* VBA
if (input == DateTime.MinValue || input == new DateTime(100, 1, 1))
{
return true;
}
return false;
}
}
For the code in your question, it would need to look like this:
public static class DateTimeExtensions
{
public static bool MinValue(this DateTime input)
{
if (input == new DateTime(1900, 1, 1))
{
return true;
}
return false;
}
}
Usage:
DateTime theDate = DateTime.Now;
// vanilla .NET
bool isMin1 = (theDate == DateTime.MinValue);
// with the extension method
bool isMin2 = theDate.MinValue();
I don't think you will be able to change the DateTime MinValue as it is read only, But if you can DON'T
DateTime:
public struct DateTime : IComparable, IFormattable, IConvertible, ISerializable, IComparable<DateTime>, IEquatable<DateTime>
{
public static readonly DateTime MaxValue
public static readonly DateTime MinValue
....
I am able to call C# methods of WebBrowser.ObjectForScripting with javascript window.external from WebBrowser WinForms control and pass string, int, bool etc. However I don't know how to pass javascript Date object and somehow convert/marshal it to .NET DateTime class.
Obviously, I could pass a string and parse it, but this is really not the point. I'm just curious how could I do it with javascript Date and .NET DateTime?
You can take advantage of the fact that dates in Javascript are expressed as the number of milliseconds elapsed since the UNIX epoch (1970-01-01 00:00:00 UTC). Use the valueOf() method to obtain that value from a Date object :
var millisecondsSinceEpoch = yourDate.valueOf();
If you can marshal that value to C# as a double, you can create the appropriate DateTime object using its constructor and the AddMilliseconds() method:
DateTime yourDateTime = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc)
.AddMilliseconds(millisecondsSinceEpoch);
I finally got it working. I don't know why, but I am unable to use it with dynamic. Here is the solution:
[ComVisible(true)]
public class Foo
{
public void Bar(object o)
{
var dateTime = (DateTime)o.GetType().InvokeMember("getVarDate", BindingFlags.InvokeMethod, null, o, null);
Console.WriteLine(dateTime);
}
}
I found better solution for my project.
in javascript:
var date = new Date();
myComObject.DoSomething(date.getVarDate());
in C#
[ComVisible(true)]
public class Foo
{
public void Bar(DateTime dateTime)
{
Console.WriteLine(dateTime);
}
}
i have an existing DateTime? object that has a datetime in it. I want to remove the datetime value from it so when you ask "HasValue" it returns false?
Nullable<T>is immutable, so you will have to reassign the variable to a different value to be able to change / remove the underlying value. This makes sense since it is a value-type (although a special one at that); value-types are normally immutable in the framework. You will notice that neither theValuenor theHasValue property forNullable<T>has a setter.
DateTime? nullableDt = DateTime.Now;
Console.WriteLine(nullableDt.HasValue); //true
nullableDt = null;
Console.WriteLine(nullableDt.HasValue); //false
or
nullableDt = new DateTime?();
Set it to null.
If you have
DateTime? value = DateTime.Now;
then call
value = null;
Why not just set it back to null?
DateTime? d = null;
System.Diagnostics.Debug.WriteLine("HasValue1 = {0}", d.HasValue); //False
d = DateTime.Now;
System.Diagnostics.Debug.WriteLine("HasValue2 = {0}", d.HasValue); //True
d = null;
System.Diagnostics.Debug.WriteLine("HasValue3 = {0}", d.HasValue); //False
The variable itself cannot be null, though you can set the minValue, it is an equivalent to '1/1/0001 00:00:00'
DateTime dvar = DateTime.MinValue;