How to convert C# nullable int to int

Question

How do I convert a nullable int to an int? Suppose I have 2 type of int as below:

int? v1;  
int v2; 

I want to assign v1's value to v2. v2 = v1; will cause an error. How do I convert v1 to v2?

Sundae

What is the desired behavior when v1 is null? – Tamarah

Answer 1

The other answers so far are all correct; I just wanted to add one more that's slightly cleaner:

v2 = v1 ?? default(int);

Any Nullable<T> is implicitly convertible to its T, PROVIDED that the entire expression being evaluated can never result in a null assignment to a ValueType. So, the null-coalescing operator ?? is just syntax sugar for the ternary operator:

v2 = v1 == null ? default(int) : v1.Value;

...which is in turn syntax sugar for an if/else:

if(v1==null)
   v2 = default(int);
else
   v2 = v1.Value;

---

Also, as of .NET 4.0, Nullable<T> has a "GetValueOrDefault()" method, which is a null-safe getter that basically performs the null-coalescing shown above, so this works too:

v2 = v1.GetValueOrDefault();

Cellar

Is default(int) really needed? What's wrong with a simple 0? – Cadge

It would work for this example, but in the general case it's recommended to use default where appropriate. Zero isn't always valid as a value, much less the default, so if you replace int with a generic T you'll find my code works while zero doesn't. In some future framework version, default may also become overloadable; if and when that happens, code using default will be easily able to take advantage, while explicit null or zero assignments will have to be changed. – Cellar

This should rise to the top: .NET 4.0, Nullable<T> has a "GetValueOrDefault()" – Clow

Thanks for coming back to edit it with GetValueOrDefault! – Reckoning

You may want to be careful with DateTime when you use default. This might insert the default date instead of empty. – Additive

Since .net 4 has been out for so long, It would be nice to edit this post so that GetValueOrDefault is shown as the main answer – Marris

by VS2019 suggestion v2 = v1 ?? default; – Aldin

link learn.microsoft.com/en-us/dotnet/api/… – Lanni

Answer 2

Like this,

if(v1.HasValue)
   v2=v1.Value

Sisk

Answer 3

You can use the Value property for assignment.

v2 = v1.Value;

Ayeaye

Also - if you're unsure if v1 contains null - you can use the null-coalescing operator to set a fallback value. E.g. v2 = v1 ?? 0; – Microscopy

And be sure to check v1.HasValue first. – Kelp

MSDN says, that this will throw an exception if the v1 is null. In my opinion, this is not a correct answer. – Sixgun

@Sixgun I would think that's desirable behavior -- I'm surprised so many of the other answers are ok with silently converting a null to 0. If you're assigning a nullable type to a non-nullable type, you should be sure that the value isn't actually null. OP didn't say "I want to assign v1 to v2, or 0 if v1 is null", but that's what everyone seemed to assume – Heracles

I don't remember which version of c# got the ! operator (null forgiveness) but due to business logic i KNOW the int? is not null. I use v2 = v1!.Value to get my value. And as @MichaelMrozek pointed out, I DO want an exception thrown, because somewhere my business got messed up. FYI I need a non null int so I can pass it to another function. – Harri

Answer 4

All you need is..

v2= v1.GetValueOrDefault();

Oberhausen

beware that this returns 0 if it's null – Pussy

Answer 5

You can't do it if v1 is null, but you can check with an operator.

v2 = v1 ?? 0;

Homemaker

this one was best useful for me – Tomahawk

Answer 6

If you know that v1 has a value, you can use the Value property:

v2 = v1.Value;

Using the GetValueOrDefault method will assign the value if there is one, otherwise the default for the type, or a default value that you specify:

v2 = v1.GetValueOrDefault(); // assigns zero if v1 has no value

v2 = v1.GetValueOrDefault(-1); // assigns -1 if v1 has no value

You can use the HasValue property to check if v1 has a value:

if (v1.HasValue) {
  v2 = v1.Value;
}

There is also language support for the GetValueOrDefault(T) method:

v2 = v1 ?? -1;

Analysand

You should not use the value without first checking to see if there is a value. Use the ?? operator instead. – Wreckful

Answer 7

GetValueOrDefault()

retrieves the value of the object. If it is null, it returns the default value of int , which is 0.

Example:

v2= v1.GetValueOrDefault();

Empoison

Answer 8

If the default value for a given type is an acceptable result:

if (v1.HasValue)
    v2 = v1.GetValueOrDefault();

If you want a different default value when the result is undefined:

v2 = v1.GetValueOrDefault(255);    // or any valid value for int in place of 255

If you just want the value returned (no matter if the method failed or not):

v2 = v1.GetValueOrDefault();

.NET 4.7.2.: GetValueOrDefault() returns the field value without any checking.

Prosenchyma

Answer 9

As far as I'm concerned the best solution is using GetValueOrDefault() method.

v2 = v1.GetValueOrDefault();

Edme

this one was best useful for me – Purple

beware that this returns 0 if it's null – Tomahawk

Answer 10

Depending on your usage context, you may use C# 7's pattern-matching feature:

int? v1 = 100;
if (v1 is int v2)
{
    Console.WriteLine($"I'm not nullable anymore: {v2}");
}

EDIT:

Since some people are downvoting without leaving an explanation, I'd like to add some details to explain the rationale for including this as a viable solution.

• C# 7's pattern matching now allows us check the type of a value and cast it implicitly. In the above snippet, the if-condition will only pass when the value stored in v1 is type-compatible to the type for v2, which in this case is int. It follows that when the value for v1 is null, the if-condition will fail since null cannot be assigned to an int. More properly, null is not an int.

• I'd like to highlight that the that this solution may not always be the optimal choice. As I suggest, I believe this will depend on the developer's exact usage context. If you already have an int? and want to conditionally operate on its value if-and-only-if the assigned value is not null (this is the only time it is safe to convert a nullable int to a regular int without losing information), then pattern matching is perhaps one of the most concise ways to do this.

Sultana

The necessity of introducing a new variable name is unfortunate, but this is the best (safest) solution if there is no default value, because there is no risk of accidentally refactoring away your HasValue checks. – Sine

I just don't see any advantage to this method over v1.HasValue as the check and then v1.Value to access the underlying value. I wouldn't downvote it, but I think this problem has been solved already and a new technique doesn't add much clarity to the problem. I also benchmarked it as 8-9% slower. – Altricial

Thanks for benchmarking it, thats good to know! Either way you look at it, the difference is marginal at best (unless you do this in some time critical area I suppose). I look at this being more "concise" or possibly "idiomatic" since it relies on syntax sugars baked into the language instead of APIs. It's a bit subjective, but perhaps it's "more maintainable". Though truly, I like this approach more than relying on a default value as a lot of other answers suggest. – Sultana

the fact that it's slower is unfortunate since this would appear to have the advantage of removing the possibility of duplicate checks, dang (edit: if it uses hard cast as the check itself, i wonder if the reason for the slowness is the underlying use of exceptions...) – Hairraising

Answer 11

Int nullable to int conversion can be done like so:

v2=(int)v1;

Aleda

If v1 is null, this will cause an InvalidOperationException. – Prosthodontics

Answer 12

In C# 7.1 and later, type can be inferred by using the default literal instead of the default operator so it can be written as below:

v2 = v1 ?? default;

Reprise

Answer 13

You could do

v2 = v1.HasValue ? v1.Value : v2;

Membranous

Answer 14

it's possible with v2 = Convert.ToInt32(v1);

Amplification

This will work technically, but other techniques such as HasValue / Value or GetValueOrDefault run much more efficiently. – Altricial

Answer 15

A simple conversion between v1 and v2 is not possible because v1 has a larger domain of values than v2. It's everything v1 can hold plus the null state. To convert you need to explicitly state what value in int will be used to map the null state. The simplest way to do this is the ?? operator

v2 = v1 ?? 0;  // maps null of v1 to 0

This can also be done in long form

int v2;
if (v1.HasValue) {
  v2 = v1.Value;
} else {
  v2 = 0;
}

Pollinate

Answer 16

It will assign value of v1 to v2 if it is not null, else it will take a default value as zero.

v2=v1??0

Or below is the other way to write it.

v2 = v1.HasValue?v1:0

Chaldean

Answer 17

It can be done using any of the following conversion methods:

v2 = Convert.ToInt32(v1);

v2 = (int)v1;

v2 = v1.GetValueOrDefault();

v2 = v1.HasValue ? v1:0;

Murine

Answer 18

I am working on C# 9 and .NET 5, example

foo is nullable int, I need get int value of foo

var foo = (context as AccountTransfer).TransferSide;
int value2 = 0;
if (foo != null)
{
    value2 = foo.Value;
}

See more at https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/builtin-types/nullable-value-types#examination-of-an-instance-of-a-nullable-value-type

Amice

Answer 19

 int v2= Int32.Parse(v1.ToString());

Calamander

While this code may answer the question, providing additional context regarding why and/or how this code answers the question improves its long-term value. – Socage

It's better to use the "best practice" way to unwrap optionals, instead of using underhanded tricks. See learn.microsoft.com/en-us/dotnet/csharp/language-reference/… for reference – Amaranthaceous

When answering a eight year old question with fifteen existing answers it is important to explain what new aspect of the question your answer is addressing, and to note if the passage of time has changed the answer. Code only answers can almost always be improved by the addition of some explanation. – Karol

I guess this is measurably slower than the other answers, with the detour through string. And still fails for a null – Aggy

I just did a simple test: roundtrip through string it is about 60 times slower than some of the other options. A whopping 100 nanoseconds! – Aggy

Answer 20

Normal TypeConversion will throw an exception

Eg:

int y = 5;    
int? x = null;    
y = x.value; //It will throw "Nullable object must have a value"   
Console.WriteLine(y);

Use Convert.ToInt32() method

int y = 5;    
int? x = null;    
y = x.Convert.ToInt32(x);    
Console.WriteLine(y);

This will return 0 as output because y is an integer.

Brahmani

Welcome to StackOverflow. There is no such thing x.Convert, please fix the provided sample. – Mikol