what does double question marks mean in c#
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What is the “??” operator for?
调试一些代码并找到??代码内部。这是什么意思?
1 2 3 4 | object obj = canBeNull ?? alternative; // equivalent to: object obj = canBeNull != null ? canBeNull : alternative; |
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 | // ?? 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"); |