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Visual Studio 2012
Application Development in Visual Studio
Quality and Diagnostic Tools
Analyzing Application Quality
Analyzing Managed Code Quality
Code Analysis for Managed Code Warnings
Usage Warnings
CA1801: Review unused parameters
CA1806: Do not ignore method results
CA1816: Call GC.SuppressFinalize correctly
CA2200: Rethrow to preserve stack details
CA2201: Do not raise reserved exception types
CA2202: Do not dispose objects multiple times
CA2204: Literals should be spelled correctly
CA2205: Use managed equivalents of Win32 API
CA2207: Initialize value type static fields inline
CA2208: Instantiate argument exceptions correctly
CA2211: Non-constant fields should not be visible
CA2212: Do not mark serviced components with WebMethod
CA2213: Disposable fields should be disposed
CA2214: Do not call overridable methods in constructors
CA2215: Dispose methods should call base class dispose
CA2216: Disposable types should declare finalizer
CA2217: Do not mark enums with FlagsAttribute
CA2218: Override GetHashCode on overriding Equals
CA2219: Do not raise exceptions in exception clauses
CA2220: Finalizers should call base class finalizer
CA2221: Finalizers should be protected
CA2222: Do not decrease inherited member visibility
CA2223: Members should differ by more than return type
CA2224: Override equals on overloading operator equals
CA2225: Operator overloads have named alternates
CA2226: Operators should have symmetrical overloads
CA2227: Collection properties should be read only
CA2228: Do not ship unreleased resource formats
CA2229: Implement serialization constructors
CA2230: Use params for variable arguments
CA2231: Overload operator equals on overriding ValueType.Equals
CA2232: Mark Windows Forms entry points with STAThread
CA2233: Operations should not overflow
CA2234: Pass System.Uri objects instead of strings
CA2235: Mark all non-serializable fields
CA2236: Call base class methods on ISerializable types
CA2237: Mark ISerializable types with SerializableAttribute
CA2238: Implement serialization methods correctly
CA2239: Provide deserialization methods for optional fields
CA2240: Implement ISerializable correctly
CA2241: Provide correct arguments to formatting methods
CA2242: Test for NaN correctly
CA2243: Attribute string literals should parse correctly
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CA2242: Test for NaN correctly

Visual Studio 2012

TypeName

TestForNaNCorrectly

CheckId

CA2242

Category

Microsoft.Usage

Breaking Change

Non Breaking

An expression tests a value against SingleNan or DoubleNan.

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

To fix a violation of this rule and accurately determine whether a value represents Double.NaN, use SingleIsNan(Single) or DoubleIsNan(Double) to test the value.

Do not suppress a warning from this rule.

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

C#
VB
Copy 
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) );
      }
   }
}
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