string? vs string in C#

Question

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();
          }
     }
}

Answer 1

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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