What does ?? operator means in C#?
Solution 1
It's the null-coalescing operator.
It returns the first argument unless it is null, in which case it returns the second.
x ?? y
is roughly equivalent to this (except that the first argument is only evaluated once):
if (x == null)
{
result = y;
}
else
{
result = x;
}
Or alternatively:
(x == null) ? y : x
It is useful for providing a default value for when a value can be null:
Color color = user.FavouriteColor ?? defaultColor;
COALESCE
When used in a LINQ to SQL query the ??
operator can be translated to a call to COALESCE. For example this LINQ query:
var query = dataContext.Table1.Select(x => x.Col1 ?? "default");
can result in this SQL query:
SELECT COALESCE([t0].[col1],@p0) AS [value]
FROM [dbo].[table1] AS [t0]
Solution 2
It is the null coalescing operator. The return value is the left hand side if it is non-null and the right hand side otherwise. It works for both reference types and nullables
var x = "foo" ?? "bar"; // "foo" wins
string y = null;
var z = y ?? "bar"; // "bar" wins
int? n = null;
var t = n ?? 5; // 5 wins
Solution 3
If something is null, it returns true, otherwise it returns something. See this link for more.
pjnovas
software developer / passion for javascript, web UI & UX / node.js enthusiast
Updated on July 09, 2022Comments
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pjnovas almost 2 years
Possible Duplicate:
What do two question marks together mean in C#?Hi, I was looking for some trainings of MVC 2 in C# and I found this sintax:
ViewData["something"] = something ?? true;
So, what is that '??' means ?.
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D'Arcy Rittich over 13 yearsSomewhat strangely,
object x = null ?? null;
is a valid statement. I guess you can't expect the compiler to do babysitting, too! -
KeithS over 13 yearsReSharper will warn you of a possible NullReferenceException if you reference a member of x after this statement, but yes, it will compile.
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pjnovas over 13 yearswow! that's a nice point hehe