为什么我不能将double初始化为null [英] Why I cannot initialize double as null

问题描述

我在程序中将double类型初始化为null

Hi,

I am initializing double type as null in my program

double utilization1=null;
            double utilization2=null;
            double utilization3=null;
            double utilization4 = null;

我在我的计划中使用以下条件

And I am using a condition as below in my program

if ((utilization1 != null) && (utilization2!=null)&&(utilization3 != null) && (utilization4!=null))
           {

            //do something
           }

我收到如下错误

I am getting error like below

Cannot convert null to 'double' because it is a non-nullable value type	

任何人都可以帮我解决这个问题

Can anyone help me in solving this problem

推荐答案

默认情况下，您会发现值类型不是可空类型（引用类型是）。要使它成为可空类型，您将声明double的方式更改为 double？。注意类型声明后的问号 - 这是将类型定义为可空的简写方式。这实际上是相当于使用 System.Nullable< double> generic来创建一个可以为空的 double 。

You'll find that the value types are not nullable types by default (reference types are). To make it a nullable type, you change the way you declare double to be double?. Notice the question mark after the type declaration - this is the shorthand way of defining a type as nullable. What this is actually doing is the equivalent of using the System.Nullable<double> generic to create a nullable type of double.

'double'是值类型，值类型不能包含空值。

如果你想用null值初始化变量那么你应该使用'double ？'而不是双倍。



加倍？ utilization1 = null;



if（utilization1.hasvalue）

{

//做某事
}

'double' is value type and value type cannot contain the null value.
If you want initialize variable with null value then you should use 'double?' instead of double.

double? utilization1=null;

if (utilization1.hasvalue)
{
//do something
}

除了使用可空的 double？之外，您还可以使用NaN（非数字）：

http：// msdn。 microsoft.com/en-us/library/system.double.nan(v=vs.110).aspx [ ^ ]，

http://msdn.microsoft.com/en-us/library/system.double.isnan （v = vs.110）.aspx [ ^ ]，

另见 http://msdn.microsoft.com/en-us/library/system.double% 28v = vs.110％29.aspx [ ^ ]。



在大多数情况下，这是最合适的方法，与使用可空类型。

-SA

In addition to using nullable double?, you can also use NaN (Not a Number):
http://msdn.microsoft.com/en-us/library/system.double.nan(v=vs.110).aspx[^],
http://msdn.microsoft.com/en-us/library/system.double.isnan(v=vs.110).aspx[^],
see also http://msdn.microsoft.com/en-us/library/system.double%28v=vs.110%29.aspx[^].

In most cases, this is the most adequate approach, lightweight compared to using the nullable type.

—SA

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