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Why is NaN not equal to NaN

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Michael
Michael 2013 年 1 月 16 日
コメント済み: Matt J 2021 年 9 月 17 日
Why is this not true?
NaN==NaN
ans =
0

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Cedric
Cedric 2013 年 1 月 16 日
編集済み: Cedric 2013 年 1 月 16 日
Most times, you don't want this test to return true indeed. Imagine testing a==b and having a true result when both a and b are undefined; this would make little sense. It is the same with NaN.
While it is not the original question, note that you can test equality assuming NaN 's are equal:
But with that you usually want to test if "behaviors" are the same (and not equality per se), e.g. if two functions return the same number or both NaN do something, else do something else.
  2 件のコメント
Matt J
Matt J 2013 年 1 月 16 日
編集済み: Matt J 2013 年 1 月 16 日
Although more recently, isequalwithequalnans has been deprecated in favor of isequaln
Cedric
Cedric 2013 年 1 月 16 日
Ah thank you, I still have 2011b and I wasn't aware (despite linking the doc for 2012b ;-/).

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その他の回答 (1 件)

Matt J
Matt J 2013 年 1 月 16 日
編集済み: Matt J 2013 年 1 月 16 日
Because equality is a notion applied to numbers. How can 2 things be equal when they are not numbers?
  7 件のコメント
math man
math man 2021 年 9 月 17 日
You might wonder, though, why NaN ~= NaN returns true?
That is, if they are not numbers why are they compared in this case to give a misleading result?
Matt J
Matt J 2021 年 9 月 17 日
@math man So you think the result of NaN ~= NaN should be NaN? Maybe.

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