c# ?? operator

最新推荐文章于 2025-08-19 15:34:11 发布

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#c# #reference #null #string #types #class

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本文详细介绍了C#中的??操作符（空合并操作符）的使用方法及应用场景。该操作符主要用于定义nullable类型及引用类型的默认值，当左操作数为null时返回右操作数，否则返回左操作数。通过具体的代码示例展示了如何应用于整型变量、字符串等不同类型的处理。

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?? Operator

The ?? operator is called the null-coalescing operator and is used to define a default value for a nullable value types as well as reference types. It returns the left-hand operand if it is not null; otherwise it returns the right operand.

class NullCoalesce
{
    static int? GetNullableInt()
    {
        return null;
    }

    static string GetStringValue()
    {
        return null;
    }

    static void Main()
    {
        // ?? operator example.
        int? x = null;

        // y = x, unless x is null, in which case y = -1.
        int y = x ?? -1;

        // Assign i to return value of method, unless
        // return value is null, in which case assign
        // default value of int to i.
        int i = GetNullableInt() ?? default(int);

        string s = GetStringValue();
        // ?? also works with reference types. 
        // Display contents of s, unless s is null, 
        // in which case display "Unspecified".
        Console.WriteLine(s ?? "Unspecified");
    }
}