C# 为什么 double.NaN 不等于自身？
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Why is double.NaN not equal to itself?
提问by Carlo
Can someone explain this to me? In C# double.NaN is not equal to double.NaN
谁可以给我解释一下这个？在 C# 中 double.NaN 不等于 double.NaN
bool huh = double.NaN == double.NaN; // huh = false
bool huh2 = double.NaN >= 0; // huh2 = false
bool huh3 = double.NaN <= 0; // huh3 = false
What constant can I compare to a double.NaN and get true?
我可以将什么常数与 double.NaN 进行比较并实现？
采纳答案by Erich Mirabal
If you are curious, this is what Double.IsNaNlooks like:
如果你很好奇，这Double.IsNaN看起来像：
public static bool IsNaN(double d)
{
return (d != d);
}
Funky, huh?
时髦吧？
回答by Adrian Godong
Use Double.IsNaN.
使用Double.IsNaN。
回答by Francis B.
bool isNaN = Double.IsNaN(yourNumber)
回答by arul
There's a specialized function for this:
有一个专门的功能：
double.IsNan(huh);
回答by David
Use the method "Double.IsNaN( value )" to check for this condition.
使用方法“Double.IsNaN(value)”来检查这种情况。
回答by Colin Mackay
Use Double.IsNan()to test for equality here. The reason is that NaN is not a number.
在这里使用Double.IsNan()测试相等性。原因是 NaN 不是数字。
回答by Mike Dinescu
回答by Torsten Marek
Actually, you already found the way to check if a IEEE-754 floating point number is NaN: it is the only floating point value (or range of values, because there are several NaNs) that evaluates to Falseif compared to itself, i.e. :
实际上，您已经找到了检查 IEEE-754 浮点数是否为NaN 的方法：它是唯一的浮点值（或值的范围，因为有几个 NaN），False如果与自身进行比较，即：
bool isNaN(double v) {
return v != v;
}
Under the hood, the Double.IsNaN method might actually do the same thing. You should still use it, because the behavior is quite surprising to anybody who does not know about the FP standard.
在幕后，Double.IsNaN 方法实际上可能会做同样的事情。您仍然应该使用它，因为对于不了解 FP 标准的任何人来说，这种行为都非常令人惊讶。
回答by Michael Meadows
The only thing that we know about NaN is that it's "Not a Number." That doesn't mean that it has a value that is associable with its state. For example:
我们对 NaN 的唯一了解是它“不是数字”。这并不意味着它具有与其状态相关联的值。例如：
∞ + (-∞) = NaN
∞ + (-∞) = NaN
0/0 = NaN
0/0 = NaN
(∞ + (-∞)) <> (0/0)
(∞ + (-∞)) <> (0/0)
Here's some C# to demonstrate
这里有一些 C# 来演示
var infinity = 100d / 0;
var negInfinity = -100d / 0;
var notANumber = infinity + negInfinity;
Console.WriteLine("Negative Infinity plus Infinity is NaN: {0}", double.IsNaN(notANumber));
var notANumber2 = 0d / 0d;
Console.WriteLine("Zero divided by Zero is NaN: {0}", double.IsNaN(notANumber2));
Console.WriteLine("These two are not equal: {0}", notANumber == notANumber2);
回答by Artru
The reason of Double.NaN != Double.NaNis simple:
原因Double.NaN != Double.NaN很简单：
Do you expect 0/0to be the same as Math.Sqrt(-3)? And same as Math.Sqrt(-7)?
你希望0/0和你一样Math.Sqrt(-3)吗？和一样Math.Sqrt(-7)吗？
There is a bug in C# in my opinion where Equals()is not overridden for NaN.
在我看来，C# 中有一个错误，Equals()没有被 NaN 覆盖。
Assert.IsTrue(Double.NaN != Double.NaN);
Assert.IsTrue(Double.NaN.Equals(Double.NaN));
At the same time
同时
Assert.IsTrue(Double.PositiveInfinity == Double.NegativeInfinity);
Assert.IsTrue(Double.PositiveInfinity.Equals(Double.PositiveInfinity));
// same for Double.NegativeInfinity and Single
Use static functions for Doubleand Single, e.g.
为Doubleand使用静态函数Single，例如
Double.IsNaN(value) && Double.IsInfinity(value);
Or more specific:
或者更具体的：
Double.IsPositiveInfinity(value);
Double.IsNegativeInfinity(value);
