C＃中兩個問號共贊成味着什麼？ - What do two question marks together mean in C#?

問題：

Ran across this line of code: 跨越這行代碼：

FormsAuth = formsAuth ?? new FormsAuthenticationWrapper();

What do the two question marks mean, is it some kind of ternary operator? 這兩個問號意味着什麼，是某種三元運算符？ It's hard to look up in Google. 谷歌很難找到。

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解決方案：

參考一： https://stackoom.com/question/1sF1/C-中兩個問號共贊成味着什麼
參考二： https://oldbug.net/q/1sF1/What-do-two-question-marks-together-mean-in-C