How can I format a nullable DateTime with ToString

Question

How can I convert the nullable DateTime dt2 to a formatted string   DateTime dt   DateTime Now  Console WriteLine dt ToString  yyyy-MM-dd hh mm ss       works  DateTime  dt2   DateTime Now  Console WriteLine dt2 ToString  yyyy-MM-dd hh mm ss       gives following error       no overload to method ToString takes   one argument

User · Answer

IFormattable also includes a format provider that can be used, it allows both format of IFormatProvider to be null in dotnet 4.0 this would be

/// <summary>
/// Extentionclass for a nullable structs
/// </summary>
public static class NullableStructExtensions {

    /// <summary>
    /// Formats a nullable struct
    /// </summary>
    /// <param name="source"></param>
    /// <param name="format">The format string 
    /// If <c>null</c> use the default format defined for the type of the IFormattable implementation.</param>
    /// <param name="provider">The format provider 
    /// If <c>null</c> the default provider is used</param>
    /// <param name="defaultValue">The string to show when the source is <c>null</c>. 
    /// If <c>null</c> an empty string is returned</param>
    /// <returns>The formatted string or the default value if the source is <c>null</c></returns>
    public static string ToString<T>(this T? source, string format = null, 
                                     IFormatProvider provider = null, 
                                     string defaultValue = null) 
                                     where T : struct, IFormattable {
        return source.HasValue
                   ? source.Value.ToString(format, provider)
                   : (String.IsNullOrEmpty(defaultValue) ? String.Empty : defaultValue);
    }
}

using together with named parameters you can do:

dt2.ToString(defaultValue: "n/a");

In older versions of dotnet you get a lot of overloads

/// <summary>
/// Extentionclass for a nullable structs
/// </summary>
public static class NullableStructExtensions {

    /// <summary>
    /// Formats a nullable struct
    /// </summary>
    /// <param name="source"></param>
    /// <param name="format">The format string 
    /// If <c>null</c> use the default format defined for the type of the IFormattable implementation.</param>
    /// <param name="provider">The format provider 
    /// If <c>null</c> the default provider is used</param>
    /// <param name="defaultValue">The string to show when the source is <c>null</c>. 
    /// If <c>null</c> an empty string is returned</param>
    /// <returns>The formatted string or the default value if the source is <c>null</c></returns>
    public static string ToString<T>(this T? source, string format, 
                                     IFormatProvider provider, string defaultValue) 
                                     where T : struct, IFormattable {
        return source.HasValue
                   ? source.Value.ToString(format, provider)
                   : (String.IsNullOrEmpty(defaultValue) ? String.Empty : defaultValue);
    }

    /// <summary>
    /// Formats a nullable struct
    /// </summary>
    /// <param name="source"></param>
    /// <param name="format">The format string 
    /// If <c>null</c> use the default format defined for the type of the IFormattable implementation.</param>
    /// <param name="defaultValue">The string to show when the source is null. If <c>null</c> an empty string is returned</param>
    /// <returns>The formatted string or the default value if the source is <c>null</c></returns>
    public static string ToString<T>(this T? source, string format, string defaultValue) 
                                     where T : struct, IFormattable {
        return ToString(source, format, null, defaultValue);
    }

    /// <summary>
    /// Formats a nullable struct
    /// </summary>
    /// <param name="source"></param>
    /// <param name="format">The format string 
    /// If <c>null</c> use the default format defined for the type of the IFormattable implementation.</param>
    /// <param name="provider">The format provider (if <c>null</c> the default provider is used)</param>
    /// <returns>The formatted string or an empty string if the source is <c>null</c></returns>
    public static string ToString<T>(this T? source, string format, IFormatProvider provider)
                                     where T : struct, IFormattable {
        return ToString(source, format, provider, null);
    }

    /// <summary>
    /// Formats a nullable struct or returns an empty string
    /// </summary>
    /// <param name="source"></param>
    /// <param name="format">The format string 
    /// If <c>null</c> use the default format defined for the type of the IFormattable implementation.</param>
    /// <returns>The formatted string or an empty string if the source is null</returns>
    public static string ToString<T>(this T? source, string format)
                                     where T : struct, IFormattable {
        return ToString(source, format, null, null);
    }

    /// <summary>
    /// Formats a nullable struct
    /// </summary>
    /// <param name="source"></param>
    /// <param name="provider">The format provider (if <c>null</c> the default provider is used)</param>
    /// <param name="defaultValue">The string to show when the source is <c>null</c>. If <c>null</c> an empty string is returned</param>
    /// <returns>The formatted string or the default value if the source is <c>null</c></returns>
    public static string ToString<T>(this T? source, IFormatProvider provider, string defaultValue)
                                     where T : struct, IFormattable {
        return ToString(source, null, provider, defaultValue);
    }

    /// <summary>
    /// Formats a nullable struct or returns an empty string
    /// </summary>
    /// <param name="source"></param>
    /// <param name="provider">The format provider (if <c>null</c> the default provider is used)</param>
    /// <returns>The formatted string or an empty string if the source is <c>null</c></returns>
    public static string ToString<T>(this T? source, IFormatProvider provider)
                                     where T : struct, IFormattable {
        return ToString(source, null, provider, null);
    }

    /// <summary>
    /// Formats a nullable struct or returns an empty string
    /// </summary>
    /// <param name="source"></param>
    /// <returns>The formatted string or an empty string if the source is <c>null</c></returns>
    public static string ToString<T>(this T? source) 
                                     where T : struct, IFormattable {
        return ToString(source, null, null, null);
    }
}

User · Answer

You can use dt2 Value ToString  format    but of course that requires that dt2    null  and that negates th use of a nullable type in the first place    There are several solutions here  but the big question is  How do you want to format a null date

User · Answer

Even a better solution in C  6 0   DateTime  birthdate   birthdate  ToString  dd MM yyyy

User · Answer

Try this on for size   The actual dateTime object your looking to format is in the dt Value property  and not on the dt2 object itself   DateTime  dt2   DateTime Now   Console WriteLine dt2 HasValue   dt2 Value ToString  yyyy-MM-dd hh mm ss       N A

User · Answer

As others have stated you need to check for null before invoking ToString but to avoid repeating yourself you could create an extension method that does that  something like   public static class DateTimeExtensions      public static string ToStringOrDefault this DateTime  source  string format  string defaultValue        if  source    null          return source Value ToString format             else         return String IsNullOrEmpty defaultValue     String Empty   defaultValue               public static string ToStringOrDefault this DateTime  source  string format           return ToStringOrDefault source  format  null            Which can be invoked like   DateTime  dt   DateTime Now  dt ToStringOrDefault  yyyy-MM-dd hh mm ss      dt ToStringOrDefault  yyyy-MM-dd hh mm ss    n a    dt   null  dt ToStringOrDefault  yyyy-MM-dd hh mm ss    n a      outputs  n a

User · Answer

What about something as easy as this   String Format   0 dd MM yyyy    d2

User · Answer

Simple generic extensions  public static class Extensions             lt summary gt          Generic method for format nullable values          lt  summary gt           lt returns gt Formated value or defaultValue lt  returns gt      public static string ToString lt T gt  this Nullable lt T gt  nullable  string format  string defaultValue   null  where T   struct               if  nullable HasValue                        return String Format   0     format        nullable Value                      return defaultValue

User · Answer

you can use simple line   dt2 ToString  d MMM yyyy

User · Answer

Here is a more generic approach  This will allow you to string format any nullable value type  I have included the second method to allow overriding the default string value instead of using the default value for the value type   public static class ExtensionMethods       public static string ToString lt T gt  this Nullable lt T gt  nullable  string format  where T   struct               return String Format   0     format        nullable GetValueOrDefault                public static string ToString lt T gt  this Nullable lt T gt  nullable  string format  string defaultValue  where T   struct               if  nullable HasValue                return String Format   0     format        nullable Value                      return defaultValue

User · Answer

C  6 0 baby   dt2  ToString  dd MM yyyy

User · Answer

Seeing that you actually want to provide the format I d suggest to add the IFormattable interface to Smalls extension method like so  that way you don t have the nasty string format concatenation   public static string ToString lt T gt  this T  variable  string format  string nullValue   null  where T  struct  IFormattable     return  variable HasValue              variable Value ToString format  null              nullValue             variable was null so return this value instead

User · Answer

Maybe it is a late answer but may help anyone else   Simple is   nullabledatevariable Value Date ToString  d     or just use any format rather than  d    Best

User · Answer

I think you have to use the GetValueOrDefault-Methode  The behaviour with ToString  yy      is not defined if the instance is null    dt2 GetValueOrDefault   ToString  yyy

User · Answer

I like this option   Console WriteLine dt2  ToString  yyyy-MM-dd hh mm ss       n a

User · Answer

Console WriteLine dt2    null   dt2 Value ToString  yyyy-MM-dd hh mm ss      n a       EDIT  As stated in other comments  check that there is a non-null value   Update  as recommended in the comments  extension method    public static string ToString this DateTime  dt  string format        gt  dt    null    n a      DateTime dt  ToString format     And starting in C  6  you can use the null-conditional operator to simplify the code even more  The expression below will return null if the DateTime  is null   dt2  ToString  yyyy-MM-dd hh mm ss

User · Answer

RAZOR syntax     myNullableDateTime  ToString  yyyy-MM-dd      String Empty

User · Answer

The problem with formulating an answer to this question is that you do not specify the desired output when the nullable datetime has no value  The following code will output DateTime MinValue in such a case  and unlike the currently accepted answer  will not throw an exception   dt2 GetValueOrDefault   ToString format

User · Answer

Shortest answer       dt yyyy-MM-dd hh mm ss     Tests  DateTime dt1   DateTime Now  Console Write  Test 1      Console WriteLine    dt1 yyyy-MM-dd hh mm ss       works  DateTime  dt2   DateTime Now  Console Write  Test 2      Console WriteLine    dt2 yyyy-MM-dd hh mm ss       Works  DateTime  dt3   null  Console Write  Test 3      Console WriteLine    dt3 yyyy-MM-dd hh mm ss       Works - Returns empty string  Output Test 1  2017-08-03 12 38 57 Test 2  2017-08-03 12 38 57 Test 3

User · Answer

Here is Blake s excellent answer as an extension method  Add this to your project and the calls in the question will work as expected  Meaning it is used like MyNullableDateTime ToString  dd MM yyyy    with the same output as MyDateTime ToString  dd MM yyyy    except that the value will be  N A  if the DateTime is null   public static string ToString this DateTime  date  string format        return date    null   date Value ToString format     N A

User · Answer

You guys are over engineering this all and making it way more complicated than it really is  Important thing  stop using ToString and start using string formatting like string Format or methods that support string formatting like Console WriteLine  Here is the preferred solution to this question  This is also the safest  Update  I update the examples with up to date methods of today s C  compiler  conditional operators  amp  string interpolation DateTime  dt1   DateTime Now  DateTime  dt2   null   Console WriteLine  quot   0 yyyy-MM-dd hh mm ss   quot   dt1   Console WriteLine  quot   0 yyyy-MM-dd hh mm ss   quot   dt2      New C  6 conditional operators  makes using  ToString safer if you must use it     https   docs microsoft com en-us dotnet csharp language-reference operators null-conditional-operators Console WriteLine dt1  ToString  quot yyyy-MM-dd hh mm ss quot     Console WriteLine dt2  ToString  quot yyyy-MM-dd hh mm ss quot        New C  6 string interpolation    https   docs microsoft com en-us dotnet csharp language-reference tokens interpolated Console WriteLine   quot   dt1 yyyy-MM-dd hh mm ss   quot    Console WriteLine   quot   dt2 yyyy-MM-dd hh mm ss   quot     Output   I put single quotes in it so you can see that it comes back as a empty string when null   2019-04-09 08 01 39     2019-04-09 08 01 39   2019-04-09 08 01 39

[c#] How can I format a nullable DateTime with ToString()?

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