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The ?? Operator

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4.50/5 (27 votes)
4 Sep 2012CPOL 79.3K   13   35
This operator is introduced to set value in place of null value, it can also be defined in words like 'In case of null, pick value from another'

Introduction

Operator is introduced with Nullable datatype inclusion in .NET Framework operator ?? can also be referred in words like 'In case of null, pick value from another'.

Scenario

Suppose you're assigning a value to Nullable bool like:

C#
bool? b = null;
At the time of checking value, it will give you an error like:

C#
if(b) //Error CS0266.
{
 
}

So it's always preferable to use ?? to prevent error like:

C#
if(b ?? false)
{
}

It defines that, in case b is null, pick the value false.

?? can also be used in multiple choice of value like:

C#
bool ? a = null
bool ? b = null
bool ? c = true
 
a = b ?? c ?? false;

That will check b first if b is undefined or null, then it will move further to check for c if that also has null then it will set false to a.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


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Comments and Discussions

 
SuggestionSome revisions? Pin
Yusuf Uzun6-Sep-12 12:30
Yusuf Uzun6-Sep-12 12:30 
GeneralRe: Some revisions? Pin
Hiren solanki6-Sep-12 20:33
Hiren solanki6-Sep-12 20:33 
GeneralMy vote of 5 Pin
WolfieH6-Sep-12 11:19
WolfieH6-Sep-12 11:19 
GeneralRe: My vote of 5 Pin
Hiren solanki6-Sep-12 20:34
Hiren solanki6-Sep-12 20:34 
GeneralMy vote of 1 Pin
Savalia Manoj M5-Sep-12 20:49
Savalia Manoj M5-Sep-12 20:49 
GeneralRe: My vote of 1 Pin
Hiren solanki5-Sep-12 21:36
Hiren solanki5-Sep-12 21:36 
GeneralRe: My vote of 1 Pin
Savalia Manoj M6-Sep-12 1:44
Savalia Manoj M6-Sep-12 1:44 
GeneralRe: My vote of 1 Pin
Hiren solanki6-Sep-12 2:56
Hiren solanki6-Sep-12 2:56 
GeneralRe: My vote of 1 Pin
Savalia Manoj M6-Sep-12 20:17
Savalia Manoj M6-Sep-12 20:17 
GeneralRe: My vote of 1 Pin
Hiren solanki6-Sep-12 20:29
Hiren solanki6-Sep-12 20:29 
GeneralRe: My vote of 1 Pin
Savalia Manoj M6-Sep-12 20:58
Savalia Manoj M6-Sep-12 20:58 
GeneralMy vote of 1 Pin
Abolfazl Khusniddinov4-Sep-12 22:52
Abolfazl Khusniddinov4-Sep-12 22:52 
GeneralRe: My vote of 1 Pin
Hiren solanki4-Sep-12 23:00
Hiren solanki4-Sep-12 23:00 
GeneralRe: My vote of 1 Pin
Andreas Gieriet5-Sep-12 3:52
professionalAndreas Gieriet5-Sep-12 3:52 
GeneralRe: My vote of 1 Pin
Hiren solanki5-Sep-12 3:58
Hiren solanki5-Sep-12 3:58 
GeneralRe: My vote of 1 Pin
Andreas Gieriet5-Sep-12 5:12
professionalAndreas Gieriet5-Sep-12 5:12 
GeneralMy vote of 4 Pin
Andreas Gieriet18-Apr-12 23:18
professionalAndreas Gieriet18-Apr-12 23:18 
GeneralReason for my vote of 5 Good to remind people about (new) la... Pin
johannesnestler21-Feb-12 3:39
johannesnestler21-Feb-12 3:39 
GeneralReason for my vote of 5 nice one Pin
Nikhil_S9-Feb-12 1:45
professionalNikhil_S9-Feb-12 1:45 
GeneralReason for my vote of 5 Simple tip; Doesn't matter if I coul... Pin
Justin Helsley6-Oct-11 9:23
Justin Helsley6-Oct-11 9:23 
GeneralReason for my vote of 5 Completly forgot about this operator... Pin
sucram16-Jan-11 22:45
sucram16-Jan-11 22:45 
GeneralAre you gonna now describe other operators as well? :) Pin
jszczur3-Jan-11 11:57
jszczur3-Jan-11 11:57 
GeneralThank you bob. Pin
Hiren solanki28-Dec-10 18:14
Hiren solanki28-Dec-10 18:14 
GeneralReason for my vote of 5 Very usefull in database data Pin
Bob Baeck28-Dec-10 9:09
professionalBob Baeck28-Dec-10 9:09 
General@SAKryukov : I am sorry,I didn't get what you're trying to c... Pin
Hiren solanki27-Dec-10 20:30
Hiren solanki27-Dec-10 20:30 

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