Checking to see if a DateTime variable has had a value assigned

Question

Is there an easy way within C  to check to see if a DateTime instance has been assigned a value or not

User · Accepted Answer

The only way of having a variable which hasn't been assigned a value in C# is for it to be a local variable - in which case at compile-time you can tell that it isn't definitely assigned by trying to read from it :)

I suspect you really want Nullable<DateTime> (or DateTime? with the C# syntactic sugar) - make it null to start with and then assign a normal DateTime value (which will be converted appropriately). Then you can just compare with null (or use the HasValue property) to see whether a "real" value has been set.

User · Answer

Use Nullable lt DateTime gt  if possible

User · Answer

I generally prefer  where possible  to use the default value of value types to determine whether they ve been set   This obviously isn t possible all the time  especially with ints - but for DateTimes  I think reserving the MinValue to signify that it hasn t been changed is fair enough   The benefit of this over nullables is that there s one less place where you ll get a null reference exception  and probably lots of places where you don t have to check for null before accessing it

User · Answer

put this somewhere   public static class DateTimeUtil   or whatever name       public static bool IsEmpty this DateTime dateTime                return dateTime    default DateTime             then   DateTime datetime         if  datetime IsEmpty            unassigned

User · Answer

I just found out that GetHashCode   for an unassigned datetime is always zero  I am not sure if this is a good way to check for null datetime  because  I can t find any documentation on why this behavior is displayed    if dt GetHashCode    0        Console WriteLine  DateTime is unassigned

User · Answer

put this somewhere   public static class DateTimeUtil   or whatever name       public static bool IsEmpty this DateTime dateTime                return dateTime    default DateTime             then   DateTime datetime         if  datetime IsEmpty            unassigned

User · Answer

I d say the default value is always new DateTime    So we can write  DateTime datetime   if  datetime    new DateTime            unassigned

User · Answer

Use Nullable lt DateTime gt  if possible

User · Answer

Use Nullable lt DateTime gt  if possible

User · Answer

I just found out that GetHashCode   for an unassigned datetime is always zero  I am not sure if this is a good way to check for null datetime  because  I can t find any documentation on why this behavior is displayed    if dt GetHashCode    0        Console WriteLine  DateTime is unassigned

User · Answer

I generally prefer  where possible  to use the default value of value types to determine whether they ve been set   This obviously isn t possible all the time  especially with ints - but for DateTimes  I think reserving the MinValue to signify that it hasn t been changed is fair enough   The benefit of this over nullables is that there s one less place where you ll get a null reference exception  and probably lots of places where you don t have to check for null before accessing it

User · Answer

If you don t want to have to worry about Null value issues like checking for null every time you use it or wrapping it up in some logic  and you also don t want to have to worry about offset time issues  then this is how I solved the problem  startDate   startDate  lt   DateTime MinValue AddSeconds 1    keepIt   resetIt  I just check that the defaulted value is less than a day after the beginning of time  Works like a charm  Edit 2021  If you need to check milliseconds of the beginning of time then just add ticks instead  but also maybe carbon dating is what you are really looking for  Still not sure carbon dating would even be as accurate as you need if you need accuracy to the tick

User · Answer

DateTime is value type  so it can not never be null  If you think DateTime    Nullable   you can use   DateTime  something   GetDateTime    bool isNull    something    null   bool isNull2    something HasValue

User · Answer

DateTime is value type  so it can not never be null  If you think DateTime    Nullable   you can use   DateTime  something   GetDateTime    bool isNull    something    null   bool isNull2    something HasValue

User · Answer

DateTime is value type  so it can not never be null  If you think DateTime    Nullable   you can use   DateTime  something   GetDateTime    bool isNull    something    null   bool isNull2    something HasValue

User · Answer

Use Nullable lt DateTime gt  if possible

User · Answer

do you mean like so   DateTime datetime   new DateTime     if  datetime    DateTime MinValue          unassigned     or you could use Nullable  DateTime  datetime   null    if   datetime HasValue            unassigned

User · Answer

do you mean like so   DateTime datetime   new DateTime     if  datetime    DateTime MinValue          unassigned     or you could use Nullable  DateTime  datetime   null    if   datetime HasValue            unassigned

User · Answer

do you mean like so   DateTime datetime   new DateTime     if  datetime    DateTime MinValue          unassigned     or you could use Nullable  DateTime  datetime   null    if   datetime HasValue            unassigned

User · Answer

DateTime is value type  so it can not never be null  If you think DateTime    Nullable   you can use   DateTime  something   GetDateTime    bool isNull    something    null   bool isNull2    something HasValue

User · Answer

I generally prefer  where possible  to use the default value of value types to determine whether they ve been set   This obviously isn t possible all the time  especially with ints - but for DateTimes  I think reserving the MinValue to signify that it hasn t been changed is fair enough   The benefit of this over nullables is that there s one less place where you ll get a null reference exception  and probably lots of places where you don t have to check for null before accessing it

User · Answer

do you mean like so   DateTime datetime   new DateTime     if  datetime    DateTime MinValue          unassigned     or you could use Nullable  DateTime  datetime   null    if   datetime HasValue            unassigned

User · Answer

If you don t want to have to worry about Null value issues like checking for null every time you use it or wrapping it up in some logic  and you also don t want to have to worry about offset time issues  then this is how I solved the problem  startDate   startDate  lt   DateTime MinValue AddSeconds 1    keepIt   resetIt  I just check that the defaulted value is less than a day after the beginning of time  Works like a charm  Edit 2021  If you need to check milliseconds of the beginning of time then just add ticks instead  but also maybe carbon dating is what you are really looking for  Still not sure carbon dating would even be as accurate as you need if you need accuracy to the tick

User · Answer

I d say the default value is always new DateTime    So we can write  DateTime datetime   if  datetime    new DateTime            unassigned

User · Answer

I generally prefer  where possible  to use the default value of value types to determine whether they ve been set   This obviously isn t possible all the time  especially with ints - but for DateTimes  I think reserving the MinValue to signify that it hasn t been changed is fair enough   The benefit of this over nullables is that there s one less place where you ll get a null reference exception  and probably lots of places where you don t have to check for null before accessing it

[c#] Checking to see if a DateTime variable has had a value assigned

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