What Does the Question Mark Mean in C# Nullable Types (int?)?

C# nullable type: the meaning of question mark

In C#, the question mark (?) is often used in conditional statements. However, it has another meaning when applied to integer equivalent types.

For example, consider the following code snippet:

<code class="language-csharp">public int? myProperty
{
   get;
   set;
}</code>

What does the question mark mean here?

Nullable type

The key to understanding the question mark here is the concept of nullable types. Nullable types are instances of the System.Nullable structure in C#. They allow us to represent a wider range of values ​​for a given type, including the possibility of null values.

For example, in the above code, int? myProperty means that myProperty is a nullable integer. This means it can hold any value in the range of integers, and can also be set to null.

Advantages and examples of nullable types

Nullable types offer many advantages, especially when working with databases or external data sources:

• Handling potential null values: Real-world data often contains missing or incomplete values. Nullable types provide a clear way to represent these values, allowing us to distinguish true zero values ​​from missing data.
• Enhanced database interoperability: Many database systems use null values ​​to represent missing data. Nullable types in C# work seamlessly with this convention, allowing efficient exchange of data between applications and databases.

The following is an example illustrating the use of nullable types:

<code class="language-csharp">class NullableExample
{
  static void Main()
  {
      int? num = null; // 表示缺失值

      // 检查 null
      if (num.HasValue)
      {
          Console.WriteLine("num = " + num.Value);
      }
      else
      {
          Console.WriteLine("num = Null");
      }
  }
}</code>

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