C#Equals()==关于数字 [英] C# Equals() == about number

问题描述

我尝试以下代码在数字比较中使用 == 和 Equals :

I try following code use == and Equals on number comparison:

Console.WriteLine( (int)2 == (double)2.0 );     
Console.WriteLine( ( (int)2 ).Equals( (double)2.0) );

Console.WriteLine((float)2.0 == (double)2.0);
Console.WriteLine( ( (float)2.0 ).Equals( (double)2.0 )   );

结果:

true 
false
true 
false

阅读帖子后，

int，double，float 均为 ValueType Here2 ，我仍然不明白为什么 == 和 Equals 得出不同的结果，

int, double, float are all ValueType, after reading posts Here1 and Here2, I still cannot understand why == and Equals turns out different result,

在这4种关于数字的情况下， == 和 Equals 背后的工作细节是什么?

What is the working detail behind == and Equals in these 4 cases about number?

(如果该问题重复，请告诉我)

(if this question is duplicate please tell me)

编辑:另外4种有趣的情况:

4 more interesting cases:

双精度浮点数<-> int

double, float <-> int

Console.WriteLine((double)2.0 == (int)2);              //True
Console.WriteLine(((double)2.0).Equals((int)2));       //True

Console.WriteLine((float)2.0 == (int)2.0);             //True
Console.WriteLine(((float)2.0).Equals((int)2.0));      //True

double，int<->浮点数

double, int <-> float

Console.WriteLine((double)2.0 == (float)2.0);          //True
Console.WriteLine(((double)2.0).Equals((float)2.0));   //True

Console.WriteLine((int)2 == (float)2.0);               //True
Console.WriteLine(((int)2).Equals((float)2.0));        //False

推荐答案

(int)2 == (double)2.0            - True because the compiler promotes int to double when comparing via ==.
((int)2).Equals( (double)2.0)    - False because this is calling int.Equals(object) and the types are different.
(float)2.0 == (double)2.0        - True because the compiler promotes float to double when comparing via ==.
((float)2.0).Equals((double)2.0) - False becaue this is calling float.Equals(object) and the types are different.
(double)2.0 == (int)2            - True because the compiler promotes int to double when comparing via ==.
((double)2.0).Equals((int)2)     - True because there exists double.Equals(double) and the compiler
                                   promotes the integer parameter 2 to double to call double.Equals(2.0).
(float)2.0 == (int)2.0           - True because the compiler promotes int to float when comparing via ==.
((float)2.0).Equals((int)2.0)    - True because there exists float.Equals(float) and the compiler
                                   promotes the integer parameter 2 to float to call float.Equals(2.0f).
(double)2.0 == (float)2.0)       - True because the compiler promotes float to double when comparing via ==.
((double)2.0).Equals((float)2.0) - True because there exists double.Equals(double) and the compiler
                                   promotes the float parameter 2.0f to double to call double.Equals(2.0).
(int)2 == (float)2.0             - True because the compiler promotes int to float when comparing via ==.
((int)2).Equals((float)2.0)      - False because this is calling int.Equals(object) and the types are different.

请注意，在返回 false 的情况下，这是因为尽管存在 int.Equals(int)，但编译器无法调用它，因为没有自动类型转换从浮点类型到 int .

Note that in the cases where false is returned, it's because although int.Equals(int) exists, the compiler cannot call it because there is no automatic type conversion from floating point types to int.

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