CA2242: Test for NaN correctly

Artigo
11/15/2016

Note

This article applies to Visual Studio 2015. If you're looking for the latest Visual Studio documentation, see Visual Studio documentation. We recommend upgrading to the latest version of Visual Studio. Download it here

Item	Value
TypeName	TestForNaNCorrectly
CheckId	CA2242
Category	Microsoft.Usage
Breaking Change	Non Breaking

Cause

An expression tests a value against System.Single.NaN or System.Double.NaN.

Rule Description

System.Double.NaN, which represents not-a-number, results when an arithmetic operation is undefined. Any expression that tests equality between a value and System.Double.NaN always returns false. Any expression that tests inequality between a value and System.Double.NaN always returns true.

How to Fix Violations

To fix a violation of this rule and accurately determine whether a value represents System.Double.NaN, use System.Single.IsNaN or System.Double.IsNaN to test the value.

When to Suppress Warnings

Do not suppress a warning from this rule.

Example

The following example shows two expressions that incorrectly test a value against System.Double.NaN and an expression that correctly uses System.Double.IsNaN to test the value.

using System;

namespace UsageLibrary
{
   class NaNTests
   {
      static double zero;
      
      static void Main()
      {
         Console.WriteLine( 0/zero == double.NaN );
         Console.WriteLine( 0/zero != double.NaN );
         Console.WriteLine( double.IsNaN(0/zero) );
      }
   }
}

Imports System

Namespace UsageLibrary

   Class NaNTests
   
      Shared zero As Double
      
      Shared Sub Main()
         Console.WriteLine( 0/zero = Double.NaN )
         Console.WriteLine( 0/zero <> Double.NaN )
         Console.WriteLine( Double.IsNaN(0/zero) )
      End Sub

   End Class

End Namespace

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