int? maxResults what does the ? means in this statement

Question

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C# - Basic question: What is ‘?’?

I have found this statement in a function arguments.

public static SyndicationFeed GetDataFeed(...... int? maxResults)

what does that means?

Answer 1

int? means it's a nullable int, so not only integer values are allowed but also the null-value.

Answer 2

Its a Nullable Type, Nullable<T>. As per MSDN

DataType int is basically a value type and cannot hold null value, but by using Nullable Type you can actually store null in it.

maxResults = null; // no syntax error

You can declare the Nullable Types by using two syntax:

int? maxResults;

OR

Nullable<int> maxResults;

Answer 3

? means nullable. It means the type can contain a value or be null.

int? num = null; // assign null to the variable num

http://msdn.microsoft.com/en-us/library/1t3y8s4s(v=vs.100).aspx

Answer 4

It's a shortcut for Nullable<int> - This means that maxResults can be assigned null.

Answer 5

Represents a int type that can be assigned null.

Answer 6

Typically an int cannot have a null value, however using the '?' prefix allows it to be Nullable:

int? myNullableInt = null; //Compiles OK
int myNonNullableInt = null; //Compiler output - Cannot convert null to 'int' because it is a non-nullable value type
int myNonNullableInt = 0; //Compiles OK

In the context of your question/code I can only assume that it is responsible for returning SyndicationFeed results based on the value of ?maxResults, however as its nullable this value could be null.

Answer 7

You cannot assign null to any value type,that includes integer.You will get an exception

int someValue;
someValue=null;//wrong and will not work

But when you make it nullable,you can assign null. To make a ValueType Nullable,you will have to follow your valuetype keyword with the symbol ?

<type>? someVariable;

int? someValue;
someValue=null;//assigns null and no issues.

Now you wont get an exception and you can assign null.