string? vs string in C#

Question

string? vs string in C#

Shervan360 1,681

Hello,

As you know, string can return null.

What is the difference between string? vs string in C#?

namespace ConsoleApp1
{
     internal class Program
     {
          static string? ReturnStringNull()
          {
               return null;
          }
          static string ReturnString()
          {
               return null;
          }
          static void Main(string[] args)
          {
               ReturnStringNull();
               ReturnString();
          }
     }
}

Screenshot 2023-07-23 015014

David Lowndes 2,745 Reputation points MVP

2023-07-23T09:25:05.8266667+00:00

In that context, the ? denotes explicit nullable. Depending on whether your project is enforcing nullability or not will determine whether a warning is indicated. Have a read here.
AnjolaOluwa Odusina 145 Reputation points

2025-10-23T18:34:30.7366667+00:00
In C#, the difference between string? and string is all about whether a value can be null.

string? means the variable can be null — you're telling the compiler it's allowed.

string means it shouldn’t ever be null — if you try to assign or return null, the compiler will warn you.

So in your example:

static string? ReturnStringNull() => null; // fine static string ReturnString() => null; // compiler warning

Basically, string? says “this might be empty, handle it carefully,” while string says “I promise it won’t be null.”

Answer accepted by question author

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David Lowndes 2,745 Reputation points MVP

2023-07-23T09:25:05.8266667+00:00

In that context, the ? denotes explicit nullable. Depending on whether your project is enforcing nullability or not will determine whether a warning is indicated. Have a read here.
AnjolaOluwa Odusina 145 Reputation points

2025-10-23T18:34:30.7366667+00:00

In C#, the difference between string? and string is all about whether a value can be null.

string? means the variable can be null — you're telling the compiler it's allowed.

string means it shouldn’t ever be null — if you try to assign or return null, the compiler will warn you.

So in your example:

static string? ReturnStringNull() => null; // fine static string ReturnString() => null; // compiler warning

Basically, string? says “this might be empty, handle it carefully,” while string says “I promise it won’t be null.”

Answer 1

Hui Liu-MSFT 48,706 Microsoft External Staff

Hi,@Shervan360 . Welcome Microsoft Q&A.

In C#, string? and string are different in terms of nullable reference types.

string?:

This represents a nullable string, which is a string that can have a value or be null.

The ? after the type indicates that the variable can be assigned a value of the specified type or be assigned null.

In C# 8.0 and later versions, nullable reference types are enabled by default, so string? is treated as a nullable string. It means the compiler will perform static analysis to help prevent null reference exceptions.

string:

This represents a regular non-nullable string, which cannot be assigned a value of null.

Without the ?, the string variable is treated as a regular string, and it must always have a valid string value.

The behavior of nullable reference types might vary depending on the version of C# and the compiler settings. Starting from C# 8.0 (Nullable reference types in C#), nullable reference types are enabled by default, but you can also control their behavior with the use of nullable annotations and nullable context options.

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Hui Liu-MSFT 48,706 Reputation points Microsoft External Staff

2023-08-01T06:46:14.6366667+00:00

Hi,@Shervan360 .Is there any update to the question? Did my answer solve your problem? If so, you could accept it as the answer. It's helpful for community members with related questions.
Oudin, Eric 0 Reputation points

2024-12-12T19:06:41.87+00:00

The answer doesn't actually answer the question and is wrong. the type of "string" can be set to null. I get "string?" following similar patterns to other objects like "int" and "int?" where int cannot be null, but with string it is different.
AnjolaOluwa Odusina 145 Reputation points

2025-10-23T19:26:52.2766667+00:00

You’re right — string can be null. The difference is that string? just tells the compiler it’s allowed and helps catch null warnings. Unlike int?, which is a different runtime type, string? is just a nullable annotation — at runtime, both are still plain string.

Answer 2

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