What does ?? mean in c#?

The ?? operator (null coalescing operator) in C# provides an alternative value for null operands: checks whether operand x is null. If x is not null, return the value of x. If x is null, returns the alternative value expression y.

The ?? operator in C# The ?? operator in

C#, also known as null merge Operator used to provide an alternative value if the operand is null.

Syntax

x ?? y

Where:

• x: The expression to check whether it is null.
• y: Alternative value expression returned if x is null.

How it works

?? The operator first checks whether x is null. If not, it will return the value of x. However, if x is null, it returns the value of the alternative value expression y.

Example

string name = null;
string defaultName = "Unknown";

string fullName = name ?? defaultName; // fullName 将为 "Unknown"，因为 name 为 null

How to use

?? operator is usually used to prevent null reference exceptions and Provides a default value when the variable is null. It can make the code more concise and safer.

Comparison with delegates

?? The operator behaves like a conditional delegate, but it is cleaner and easier to read. The following code uses delegates to achieve the same function:

string name = null;
string defaultName = "Unknown";

Func<string, string> getName = (n) => n ?? defaultName;
string fullName = getName(name);

Advantages

• Concise and clear
• Reduce null reference exceptions
• Enhance code readability

Disadvantages

• may cause confusion if x is not a reference type, or y The type of is incompatible with x.
• Cannot specify multiple alternate values.

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