Exception Exception Exception Exception Class

Definition

public ref class Exception : System::Runtime::InteropServices::_Exception, System::Runtime::Serialization::ISerializable

[System.Runtime.InteropServices.ClassInterface(System.Runtime.InteropServices.ClassInterfaceType.None)]
[System.Runtime.InteropServices.ComVisible(true)]
[System.Runtime.InteropServices.ClassInterface(System.Runtime.InteropServices.ClassInterfaceType.AutoDual)]
public class Exception : System.Runtime.InteropServices._Exception, System.Runtime.Serialization.ISerializable

type Exception = class
    interface ISerializable
    interface _Exception

Public Class Exception
Implements _Exception, ISerializable

Inheritance

ObjectObjectObjectObject

ExceptionExceptionExceptionException

Derived

Microsoft.Build.BuildEngine.InternalLoggerExceptionMicrosoft.Build.BuildEngine.InternalLoggerExceptionMicrosoft.Build.BuildEngine.InternalLoggerExceptionMicrosoft.Build.BuildEngine.InternalLoggerException

Microsoft.Build.BuildEngine.InvalidProjectFileExceptionMicrosoft.Build.BuildEngine.InvalidProjectFileExceptionMicrosoft.Build.BuildEngine.InvalidProjectFileExceptionMicrosoft.Build.BuildEngine.InvalidProjectFileException

Microsoft.Build.BuildEngine.InvalidToolsetDefinitionExceptionMicrosoft.Build.BuildEngine.InvalidToolsetDefinitionExceptionMicrosoft.Build.BuildEngine.InvalidToolsetDefinitionExceptionMicrosoft.Build.BuildEngine.InvalidToolsetDefinitionException

Microsoft.Build.BuildEngine.RemoteErrorExceptionMicrosoft.Build.BuildEngine.RemoteErrorExceptionMicrosoft.Build.BuildEngine.RemoteErrorExceptionMicrosoft.Build.BuildEngine.RemoteErrorException

Microsoft.Build.Exceptions.BuildAbortedExceptionMicrosoft.Build.Exceptions.BuildAbortedExceptionMicrosoft.Build.Exceptions.BuildAbortedExceptionMicrosoft.Build.Exceptions.BuildAbortedException

More…

Attributes

ClassInterfaceAttribute ComVisibleAttribute ClassInterfaceAttribute

Implements

_Exception_Exception_Exception_Exception ISerializableISerializableISerializableISerializable

Examples

The following example demonstrates a catch block that is defined to handle ArithmeticException errors. This catch block also catches DivideByZeroException errors, because DivideByZeroException derives from ArithmeticException and there is no catch block explicitly defined for DivideByZeroException errors.

using namespace System;
int main()
{
    int x = 0;
    try
    {
        int y = 100 / x;
    }
    catch ( ArithmeticException^ e ) 
    {
        Console::WriteLine( "ArithmeticException Handler: {0}", e );
    }
    catch ( Exception^ e ) 
    {
        Console::WriteLine( "Generic Exception Handler: {0}", e );
    }
}
/*
This code example produces the following results:

ArithmeticException Handler: System.DivideByZeroException: Attempted to divide by zero.
   at main()
 
*/

using System;

class ExceptionTestClass 
{
   public static void Main() 
   {
      int x = 0;
      try 
      {
         int y = 100/x;
      }
         catch (ArithmeticException e) 
         {
            Console.WriteLine("ArithmeticException Handler: {0}", e.ToString());
         }
         catch (Exception e) 
         {
            Console.WriteLine("Generic Exception Handler: {0}", e.ToString());
         }
   }	
}
/*
This code example produces the following results:

ArithmeticException Handler: System.DivideByZeroException: Attempted to divide by zero.
   at ExceptionTestClass.Main()

*/

Imports System

Class ExceptionTestClass
   
   Public Shared Sub Main()
      Dim x As Integer = 0
      Try
         Dim y As Integer = 100 / x
      Catch e As ArithmeticException
         Console.WriteLine("ArithmeticException Handler: {0}", e.ToString())
      Catch e As Exception
         Console.WriteLine("Generic Exception Handler: {0}", e.ToString())
      End Try
   End Sub 'Main
End Class 'ExceptionTestClass
'
'This code example produces the following results:
'
'ArithmeticException Handler: System.OverflowException: Arithmetic operation resulted in an overflow.
'   at ExceptionTestClass.Main()
'

Remarks

This class is the base class for all exceptions. When an error occurs, either the system or the currently executing application reports it by throwing an exception that contains information about the error. After an exception is thrown, it is handled by the application or by the default exception handler.

In this section:

Errors and exceptions
Try/catch blocks
Exception type features
Exception class properties
Performance considerations
Re-throwing an exception
Choosing standard exceptions
Implementing custom exceptions

Errors and exceptions

Run-time errors can occur for a variety of reasons. However, not all errors should be handled as exceptions in your code. Here are some categories of errors that can occur at run time and the appropriate ways to respond to them.

• Usage errors. A usage error represents an error in program logic that can result in an exception. However, the error should be addressed not through exception handling but by modifying the faulty code. For example, the override of the Object.Equals(Object) method in the following example assumes that the obj argument must always be non-null.

  using System;
  
  public class Person
  {
     private string _name;
     
     public string Name 
     {
        get { return _name; } 
        set { _name = value; }
     }
     
     public override int GetHashCode()
     {
        return this.Name.GetHashCode();  
     }  
                          
     public override bool Equals(object obj)
     {
        // This implementation contains an error in program logic:
        // It assumes that the obj argument is not null.
        Person p = (Person) obj;
        return this.Name.Equals(p.Name);
     }
  }
  
  public class Example
  {
     public static void Main()
     {
        Person p1 = new Person();
        p1.Name = "John";
        Person p2 = null; 
        
        // The following throws a NullReferenceException.
        Console.WriteLine("p1 = p2: {0}", p1.Equals(p2));   
     }
  }
  

  Public Class Person
     Private _name As String
     
     Public Property Name As String
        Get
           Return _name
        End Get
        Set
           _name = value
        End Set
     End Property
     
     Public Overrides Function Equals(obj As Object) As Boolean
        ' This implementation contains an error in program logic:
        ' It assumes that the obj argument is not null.
        Dim p As Person = CType(obj, Person)
        Return Me.Name.Equals(p.Name)
     End Function
  End Class
  
  Module Example
     Public Sub Main()
        Dim p1 As New Person()
        p1.Name = "John"
        Dim p2 As Person = Nothing
        
        ' The following throws a NullReferenceException.
        Console.WriteLine("p1 = p2: {0}", p1.Equals(p2))   
     End Sub
  End Module
  

  The NullReferenceException exception that results when obj is null can be eliminated by modifying the source code to explicitly test for null before calling the Object.Equals override and then re-compiling. The following example contains the corrected source code that handles a null argument.

  using System;
  
  public class Person
  {
     private string _name;
     
     public string Name 
     {
        get { return _name; } 
        set { _name = value; }
     }
     
     public override int GetHashCode()
     {
        return this.Name.GetHashCode();  
     }  
                          
     public override bool Equals(object obj)
     {
         // This implementation handles a null obj argument.
         Person p = obj as Person; 
         if (p == null) 
            return false;
         else
            return this.Name.Equals(p.Name);
     }
  }
  
  public class Example
  {
     public static void Main()
     {
        Person p1 = new Person();
        p1.Name = "John";
        Person p2 = null; 
        
        Console.WriteLine("p1 = p2: {0}", p1.Equals(p2));   
     }
  }
  // The example displays the following output:
  //        p1 = p2: False
  

  Public Class Person
     Private _name As String
     
     Public Property Name As String
        Get
           Return _name
        End Get
        Set
           _name = value
        End Set
     End Property
     
     Public Overrides Function Equals(obj As Object) As Boolean
        ' This implementation handles a null obj argument.
        Dim p As Person = TryCast(obj, Person)
        If p Is Nothing Then 
           Return False
        Else
           Return Me.Name.Equals(p.Name)
        End If
     End Function
  End Class
  
  Module Example
     Public Sub Main()
        Dim p1 As New Person()
        p1.Name = "John"
        Dim p2 As Person = Nothing
        
        Console.WriteLine("p1 = p2: {0}", p1.Equals(p2))   
     End Sub
  End Module
  ' The example displays the following output:
  '       p1 = p2: False
  

  Instead of using exception handling for usage errors, you can use the Debug.Assert method to identify usage errors in debug builds, and the Trace.Assert method to identify usage errors in both debug and release builds. For more information, see Assertions in Managed Code.

• Program errors. A program error is a run-time error that cannot necessarily be avoided by writing bug-free code.

  In some cases, a program error may reflect an expected or routine error condition. In this case, you may want to avoid using exception handling to deal with the program error and instead retry the operation. For example, if the user is expected to input a date in a particular format, you can parse the date string by calling the DateTime.TryParseExact method, which returns a Boolean value that indicates whether the parse operation succeeded, instead of using the DateTime.ParseExact method, which throws a FormatException exception if the date string cannot be converted to a DateTime value. Similarly, if a user tries to open a file that does not exist, you can first call the File.Exists method to check whether the file exists and, if it does not, prompt the user whether he or she wants to create it.

  In other cases, a program error reflects an unexpected error condition that can be handled in your code. For example, even if you've checked to ensure that a file exists, it may be deleted before you can open it, or it may be corrupted. In that case, trying to open the file by instantiating a StreamReader object or calling the Open method may throw a FileNotFoundException exception. In these cases, you should use exception handling to recover from the error.

• System failures. A system failure is a run-time error that cannot be handled programmatically in a meaningful way. For example, any method can throw an OutOfMemoryException exception if the common language runtime is unable to allocate additional memory. Ordinarily, system failures are not handled by using exception handling. Instead, you may be able to use an event such as AppDomain.UnhandledException and call the Environment.FailFast method to log exception information and notify the user of the failure before the application terminates.

Try/catch blocks

The common language runtime provides an exception handling model that is based on the representation of exceptions as objects, and the separation of program code and exception handling code into try blocks and catch blocks. There can be one or more catch blocks, each designed to handle a particular type of exception, or one block designed to catch a more specific exception than another block.

If an application handles exceptions that occur during the execution of a block of application code, the code must be placed within a try statement and is called a try block. Application code that handles exceptions thrown by a try block is placed within a catch statement and is called a catch block. Zero or more catch blocks are associated with a try block, and each catch block includes a type filter that determines the types of exceptions it handles.

When an exception occurs in a try block, the system searches the associated catch blocks in the order they appear in application code, until it locates a catch block that handles the exception. A catch block handles an exception of type T if the type filter of the catch block specifies T or any type that T derives from. The system stops searching after it finds the first catch block that handles the exception. For this reason, in application code, a catch block that handles a type must be specified before a catch block that handles its base types, as demonstrated in the example that follows this section. A catch block that handles System.Exception is specified last.

If none of the catch blocks associated with the current try block handle the exception, and the current try block is nested within other try blocks in the current call, the catch blocks associated with the next enclosing try block are searched. If no catch block for the exception is found, the system searches previous nesting levels in the current call. If no catch block for the exception is found in the current call, the exception is passed up the call stack, and the previous stack frame is searched for a catch block that handles the exception. The search of the call stack continues until the exception is handled or until no more frames exist on the call stack. If the top of the call stack is reached without finding a catch block that handles the exception, the default exception handler handles it and the application terminates.

Exception type features

Exception types support the following features:

• Human-readable text that describes the error. When an exception occurs, the runtime makes a text message available to inform the user of the nature of the error and to suggest action to resolve the problem. This text message is held in the Message property of the exception object. During the creation of the exception object, you can pass a text string to the constructor to describe the details of that particular exception. If no error message argument is supplied to the constructor, the default error message is used. For more information, see the Message property.

• The state of the call stack when the exception was thrown. The StackTrace property carries a stack trace that can be used to determine where the error occurs in the code. The stack trace lists all the called methods and the line numbers in the source file where the calls are made.

Exception class properties

The Exception class includes a number of properties that help identify the code location, the type, the help file, and the reason for the exception: StackTrace, InnerException, Message, HelpLink, HResult, Source, TargetSite, and Data.

When a causal relationship exists between two or more exceptions, the InnerException property maintains this information. The outer exception is thrown in response to this inner exception. The code that handles the outer exception can use the information from the earlier inner exception to handle the error more appropriately. Supplementary information about the exception can be stored as a collection of key/value pairs in the Data property.

The error message string that is passed to the constructor during the creation of the exception object should be localized and can be supplied from a resource file by using the ResourceManager class. For more information about localized resources, see the Creating Satellite Assemblies and Packaging and Deploying Resources topics.

To provide the user with extensive information about why the exception occurred, the HelpLink property can hold a URL (or URN) to a help file.

The Exception class uses the HRESULT COR_E_EXCEPTION, which has the value 0x80131500.

For a list of initial property values for an instance of the Exception class, see the Exception constructors.

Performance considerations

Throwing or handling an exception consumes a significant amount of system resources and execution time. Throw exceptions only to handle truly extraordinary conditions, not to handle predictable events or flow control. For example, in some cases, such as when you're developing a class library, it's reasonable to throw an exception if a method argument is invalid, because you expect your method to be called with valid parameters. An invalid method argument, if it is not the result of a usage error, means that something extraordinary has occurred. Conversely, do not throw an exception if user input is invalid, because you can expect users to occasionally enter invalid data. Instead, provide a retry mechanism so users can enter valid input. Nor should you use exceptions to handle usage errors. Instead, use assertions to identify and correct usage errors.

In addition, do not throw an exception when a return code is sufficient; do not convert a return code to an exception; and do not routinely catch an exception, ignore it, and then continue processing.

Re-throwing an exception

In many cases, an exception handler simply wants to pass the exception on to the caller. This most often occurs in:

• A class library that in turn wraps calls to methods in the .NET Framework class library or other class libraries.

• An application or library that encounters a fatal exception. The exception handler can log the exception and then re-throw the exception.

The recommended way to re-throw an exception is to simply use the throw statement in C# and the Throw statement in Visual Basic without including an expression. This ensures that all call stack information is preserved when the exception is propagated to the caller. The following example illustrates this. A string extension method, FindOccurrences, wraps one or more calls to String.IndexOf(String, Int32) without validating its arguments beforehand.

using System;
using System.Collections.Generic;
using System.Runtime.CompilerServices;

public static class Library
{
   public static int[] FindOccurrences(this String s, String f)
   {
      var indexes = new List<int>();
      int currentIndex = 0;
      try {
         while (currentIndex >= 0 && currentIndex < s.Length) {
            currentIndex = s.IndexOf(f, currentIndex);
            if (currentIndex >= 0) {
               indexes.Add(currentIndex);
               currentIndex++;
            }
         }
      }
      catch (ArgumentNullException e) {
         // Perform some action here, such as logging this exception.

         throw;
      }
      return indexes.ToArray();
   }
}

Imports System.Collections.Generic
Imports System.Runtime.CompilerServices

Public Module Library
   <Extension()>
   Public Function FindOccurrences(s As String, f As String) As Integer()
      Dim indexes As New List(Of Integer)
      Dim currentIndex As Integer = 0
      Try
         Do While currentIndex >= 0 And currentIndex < s.Length
            currentIndex = s.IndexOf(f, currentIndex)
            If currentIndex >= 0 Then
               indexes.Add(currentIndex)
               currentIndex += 1
            End If
         Loop
      Catch e As ArgumentNullException
         ' Perform some action here, such as logging this exception.
         
         Throw
      End Try
      Return indexes.ToArray()
   End Function
End Module

A caller then calls FindOccurrences twice. In the second call to FindOccurrences, the caller passes a null as the search string, which cases the String.IndexOf(String, Int32) method to throw an ArgumentNullException exception. This exception is handled by the FindOccurrences method and passed back to the caller. Because the throw statement is used with no expression, the output from the example shows that the call stack is preserved.

public class Example
{
   public static void Main()
   {
      String s = "It was a cold day when...";
      int[] indexes = s.FindOccurrences("a");
      ShowOccurrences(s, "a", indexes);
      Console.WriteLine();
      
      String toFind = null;
      try {
         indexes = s.FindOccurrences(toFind);
         ShowOccurrences(s, toFind, indexes);
      }
      catch (ArgumentNullException e) {
         Console.WriteLine("An exception ({0}) occurred.",
                           e.GetType().Name);
         Console.WriteLine("Message:\n   {0}\n", e.Message);
         Console.WriteLine("Stack Trace:\n   {0}\n", e.StackTrace);
      }
   }

   private static void ShowOccurrences(String s, String toFind, int[] indexes)
   {
      Console.Write("'{0}' occurs at the following character positions: ",
                    toFind);
      for (int ctr = 0; ctr < indexes.Length; ctr++)
         Console.Write("{0}{1}", indexes[ctr],
                       ctr == indexes.Length - 1 ? "" : ", ");

      Console.WriteLine();
   }
}
// The example displays the following output:
//    'a' occurs at the following character positions: 4, 7, 15
//
//    An exception (ArgumentNullException) occurred.
//    Message:
//       Value cannot be null.
//    Parameter name: value
//
//    Stack Trace:
//          at System.String.IndexOf(String value, Int32 startIndex, Int32 count, Stri
//    ngComparison comparisonType)
//       at Library.FindOccurrences(String s, String f)
//       at Example.Main()

Module Example
   Public Sub Main()
      Dim s As String = "It was a cold day when..."
      Dim indexes() As Integer = s.FindOccurrences("a")
      ShowOccurrences(s, "a", indexes)
      Console.WriteLine()

      Dim toFind As String = Nothing
      Try
         indexes = s.FindOccurrences(toFind)
         ShowOccurrences(s, toFind, indexes)
      Catch e As ArgumentNullException
         Console.WriteLine("An exception ({0}) occurred.",
                           e.GetType().Name)
         Console.WriteLine("Message:{0}   {1}{0}", vbCrLf, e.Message)
         Console.WriteLine("Stack Trace:{0}   {1}{0}", vbCrLf, e.StackTrace)
      End Try
   End Sub
   
   Private Sub ShowOccurrences(s As String, toFind As String, indexes As Integer())
      Console.Write("'{0}' occurs at the following character positions: ",
                    toFind)
      For ctr As Integer = 0 To indexes.Length - 1
         Console.Write("{0}{1}", indexes(ctr),
                       If(ctr = indexes.Length - 1, "", ", "))
      Next
      Console.WriteLine()
   End Sub
End Module
' The example displays the following output:
'    'a' occurs at the following character positions: 4, 7, 15
'
'    An exception (ArgumentNullException) occurred.
'    Message:
'       Value cannot be null.
'    Parameter name: value
'
'    Stack Trace:
'          at System.String.IndexOf(String value, Int32 startIndex, Int32 count, Stri
'    ngComparison comparisonType)
'       at Library.FindOccurrences(String s, String f)
'       at Example.Main()

In contrast, if the exception is re-thrown by using the

throw e  

Throw e  

statement, the full call stack is not preserved, and the example would generate the following output:

'a' occurs at the following character positions: 4, 7, 15  

An exception (ArgumentNullException) occurred.  
Message:  
   Value cannot be null.  
Parameter name: value  

Stack Trace:  
      at Library.FindOccurrences(String s, String f)  
   at Example.Main()  

A slightly more cumbersome alternative is to throw a new exception, and to preserve the original exception's call stack information in an inner exception. The caller can then use the new exception's InnerException property to retrieve stack frame and other information about the original exception. In this case, the throw statement is:

throw new ArgumentNullException("You must supply a search string.",
                                e);

Throw New ArgumentNullException("You must supply a search string.",
                                e)

The user code that handles the exception has to know that the InnerException property contains information about the original exception, as the following exception handler illustrates.

try {
   indexes = s.FindOccurrences(toFind);
   ShowOccurrences(s, toFind, indexes);
}
catch (ArgumentNullException e) {
   Console.WriteLine("An exception ({0}) occurred.",
                     e.GetType().Name);
   Console.WriteLine("   Message:\n{0}", e.Message);
   Console.WriteLine("   Stack Trace:\n   {0}", e.StackTrace);
   Exception ie = e.InnerException;
   if (ie != null) {
      Console.WriteLine("   The Inner Exception:");
      Console.WriteLine("      Exception Name: {0}", ie.GetType().Name);
      Console.WriteLine("      Message: {0}\n", ie.Message);
      Console.WriteLine("      Stack Trace:\n   {0}\n", ie.StackTrace);
   }
}
// The example displays the following output:
//    'a' occurs at the following character positions: 4, 7, 15
//
//    An exception (ArgumentNullException) occurred.
//       Message: You must supply a search string.
//
//       Stack Trace:
//          at Library.FindOccurrences(String s, String f)
//       at Example.Main()
//
//       The Inner Exception:
//          Exception Name: ArgumentNullException
//          Message: Value cannot be null.
//    Parameter name: value
//
//          Stack Trace:
//          at System.String.IndexOf(String value, Int32 startIndex, Int32 count, Stri
//    ngComparison comparisonType)
//       at Library.FindOccurrences(String s, String f)

Try
   indexes = s.FindOccurrences(toFind)
   ShowOccurrences(s, toFind, indexes)
Catch e As ArgumentNullException
   Console.WriteLine("An exception ({0}) occurred.",
                     e.GetType().Name)
   Console.WriteLine("   Message: {1}{0}", vbCrLf, e.Message)
   Console.WriteLine("   Stack Trace:{0}   {1}{0}", vbCrLf, e.StackTrace)
   Dim ie As Exception = e.InnerException
   If ie IsNot Nothing Then
      Console.WriteLine("   The Inner Exception:")
      Console.WriteLine("      Exception Name: {0}", ie.GetType().Name)
      Console.WriteLine("      Message: {1}{0}", vbCrLf, ie.Message)
      Console.WriteLine("      Stack Trace:{0}   {1}{0}", vbCrLf, ie.StackTrace)
   End If
End Try
' The example displays the following output:
'       'a' occurs at the following character positions: 4, 7, 15
'
'       An exception (ArgumentNullException) occurred.
'          Message: You must supply a search string.
'
'          Stack Trace:
'             at Library.FindOccurrences(String s, String f)
'          at Example.Main()
'
'          The Inner Exception:
'             Exception Name: ArgumentNullException
'             Message: Value cannot be null.
'       Parameter name: value
'
'             Stack Trace:
'             at System.String.IndexOf(String value, Int32 startIndex, Int32 count, Stri
'       ngComparison comparisonType)
'          at Library.FindOccurrences(String s, String f)

Choosing standard exceptions

When you have to throw an exception, you can often use an existing exception type in the .NET Framework instead of implementing a custom exception. You should use a standard exception type under these two conditions:

• You are throwing an exception that is caused by a usage error (that is, by an error in program logic made by the developer who is calling your method). Typically, you would throw an exception such as ArgumentException, ArgumentNullException, InvalidOperationException, or NotSupportedException. The string you supply to the exception object's constructor when instantiating the exception object should describe the error so that the developer can fix it. For more information, see the Message property.

• You are handling an error that can be communicated to the caller with an existing .NET Framework exception. You should throw the most derived exception possible. For example, if a method requires an argument to be a valid member of an enumeration type, you should throw an InvalidEnumArgumentException (the most derived class) rather than an ArgumentException.

The following table lists common exception types and the conditions under which you would throw them.

Implementing custom exceptions

In the following cases, using an existing .NET Framework exception to handle an error condition is not adequate:

• When the exception reflects a unique program error that cannot be mapped to an existing .NET Framework exception.

• When the exception requires handling that is different from the handling that is appropriate for an existing .NET Framework exception, or the exception must be disambiguated from a similar exception. For example, if you throw an ArgumentOutOfRangeException exception when parsing the numeric representation of a string that is out of range of the target integral type, you would not want to use the same exception for an error that results from the caller not supplying the appropriate constrained values when calling the method.

The Exception class is the base class of all exceptions in the .NET Framework. Many derived classes rely on the inherited behavior of the members of the Exception class; they do not override the members of Exception, nor do they define any unique members.

To define your own exception class:

1. Define a class that inherits from Exception. If necessary, define any unique members needed by your class to provide additional information about the exception. For example, the ArgumentException class includes a ParamName property that specifies the name of the parameter whose argument caused the exception, and the RegexMatchTimeoutException property includes a MatchTimeout property that indicates the time-out interval.

2. If necessary, override any inherited members whose functionality you want to change or modify. Note that most existing derived classes of Exception do not override the behavior of inherited members.

3. Determine whether your custom exception object is serializable. Serialization enables you to save information about the exception and permits exception information to be shared by a server and a client proxy in a remoting context. To make the exception object serializable, mark it with the SerializableAttribute attribute.

4. Define the constructors of your exception class. Typically, exception classes have one or more of the following constructors:

   • Exception(), which uses default values to initialize the properties of a new exception object.

   • Exception(String), which initializes a new exception object with a specified error message.

   • Exception(String, Exception), which initializes a new exception object with a specified error message and inner exception.

   • Exception(SerializationInfo, StreamingContext), which is a protected constructor that initializes a new exception object from serialized data. You should implement this constructor if you've chosen to make your exception object serializable.

The following example illustrates the use of a custom exception class. It defines a NotPrimeException exception that is thrown when a client tries to retrieve a sequence of prime numbers by specifying a starting number that is not prime. The exception defines a new property, NonPrime, that returns the non-prime number that caused the exception. Besides implementing a protected parameterless constructor and a constructor with SerializationInfo and StreamingContext parameters for serialization, the NotPrimeException class defines three additional constructors to support the NonPrime property. Each constructor calls a base class constructor in addition to preserving the value of the non-prime number. The NotPrimeException class is also marked with the SerializableAttribute attribute.

using System;
using System.Runtime.Serialization;

[Serializable()]
public class NotPrimeException : Exception
{
   private int notAPrime;

   protected NotPrimeException()
      : base()
   { }

   public NotPrimeException(int value) :
      base(String.Format("{0} is not a prime number.", value))
   {
      notAPrime = value;
   }

   public NotPrimeException(int value, string message)
      : base(message)
   {
      notAPrime = value;
   }

   public NotPrimeException(int value, string message, Exception innerException) :
      base(message, innerException)
   {
      notAPrime = value;
   }

   protected NotPrimeException(SerializationInfo info,
                               StreamingContext context)
      : base(info, context)
   { }

   public int NonPrime
   { get { return notAPrime; } }
}

Imports System.Runtime.Serialization

<Serializable()> _
Public Class NotPrimeException : Inherits Exception
   Private notAPrime As Integer

   Protected Sub New()
      MyBase.New()
   End Sub

   Public Sub New(value As Integer)
      MyBase.New(String.Format("{0} is not a prime number.", value))
      notAPrime = value
   End Sub

   Public Sub New(value As Integer, message As String)
      MyBase.New(message)
      notAPrime = value
   End Sub

   Public Sub New(value As Integer, message As String, innerException As Exception)
      MyBase.New(message, innerException)
      notAPrime = value
   End Sub

   Protected Sub New(info As SerializationInfo,
                     context As StreamingContext)
      MyBase.New(info, context)
   End Sub

   Public ReadOnly Property NonPrime As Integer
      Get
         Return notAPrime
      End Get
   End Property
End Class

The PrimeNumberGenerator class shown in the following example uses the Sieve of Eratosthenes to calculate the sequence of prime numbers from 2 to a limit specified by the client in the call to its class constructor. The GetPrimesFrom method returns all prime numbers that are greater than or equal to a specified lower limit, but throws a NotPrimeException if that lower limit is not a prime number.

using System;
using System.Collections.Generic;


[Serializable]
public class PrimeNumberGenerator
{
   private const int START = 2;
   private int maxUpperBound = 10000000;
   private int upperBound;
   private bool[] primeTable;
   private List<int> primes = new List<int>();

   public PrimeNumberGenerator(int upperBound)
   {
      if (upperBound > maxUpperBound)
      {
         string message = String.Format(
                           "{0} exceeds the maximum upper bound of {1}.",
                           upperBound, maxUpperBound);
         throw new ArgumentOutOfRangeException(message);
      }
      this.upperBound = upperBound;
      // Create array and mark 0, 1 as not prime (True).
      primeTable = new bool[upperBound + 1];
      primeTable[0] = true;
      primeTable[1] = true;

      // Use Sieve of Eratosthenes to determine prime numbers.
      for (int ctr = START; ctr <= (int)Math.Ceiling(Math.Sqrt(upperBound));
            ctr++)
      {
         if (primeTable[ctr]) continue;

         for (int multiplier = ctr; multiplier <= upperBound / ctr; multiplier++)
            if (ctr * multiplier <= upperBound) primeTable[ctr * multiplier] = true;
      }
      // Populate array with prime number information.
      int index = START;
      while (index != -1)
      {
         index = Array.FindIndex(primeTable, index, (flag) => !flag);
         if (index >= 1)
         {
            primes.Add(index);
            index++;
         }
      }
   }

   public int[] GetAllPrimes()
   {
      return primes.ToArray();
   }

   public int[] GetPrimesFrom(int prime)
   {
      int start = primes.FindIndex((value) => value == prime);
      if (start < 0)
         throw new NotPrimeException(prime, String.Format("{0} is not a prime number.", prime));
      else
         return primes.FindAll((value) => value >= prime).ToArray();
   }
}

Imports System.Collections.Generic

<Serializable()> Public Class PrimeNumberGenerator
   Private Const START As Integer = 2
   Private maxUpperBound As Integer = 10000000
   Private upperBound As Integer
   Private primeTable() As Boolean
   Private primes As New List(Of Integer)

   Public Sub New(upperBound As Integer)
      If upperBound > maxUpperBound Then
         Dim message As String = String.Format(
             "{0} exceeds the maximum upper bound of {1}.",
             upperBound, maxUpperBound)
         Throw New ArgumentOutOfRangeException(message)
      End If
      Me.upperBound = upperBound
      ' Create array and mark 0, 1 as not prime (True).
      ReDim primeTable(upperBound)
      primeTable(0) = True
      primeTable(1) = True

      ' Use Sieve of Eratosthenes to determine prime numbers.
      For ctr As Integer = START To CInt(Math.Ceiling(Math.Sqrt(upperBound)))
         If primeTable(ctr) Then Continue For

         For multiplier As Integer = ctr To CInt(upperBound \ ctr)
            If ctr * multiplier <= upperBound Then primeTable(ctr * multiplier) = True
         Next
      Next
      ' Populate array with prime number information.
      Dim index As Integer = START
      Do While index <> -1
         index = Array.FindIndex(primeTable, index, Function(flag)
                                                       Return Not flag
                                                    End Function)
         If index >= 1 Then
            primes.Add(index)
            index += 1
         End If
      Loop
   End Sub

   Public Function GetAllPrimes() As Integer()
      Return primes.ToArray()
   End Function

   Public Function GetPrimesFrom(prime As Integer) As Integer()
      Dim start As Integer = primes.FindIndex(Function(value)
                                                 Return value = prime
                                              End Function)
      If start < 0 Then
         Throw New NotPrimeException(prime, String.Format("{0} is not a prime number.", prime))
      Else
         Return primes.FindAll(Function(value)
                                  Return value >= prime
                               End Function).ToArray()
      End If
   End Function
End Class

The following example makes two calls to the GetPrimesFrom method with non-prime numbers, one of which crosses application domain boundaries. In both cases, the exception is thrown and successfully handled in client code.

using System;
using System.Reflection;

class Example
{
   public static void Main()
   {
      int limit = 10000000;
      PrimeNumberGenerator primes = new PrimeNumberGenerator(limit);
      int start = 1000001;
      try
      {
         int[] values = primes.GetPrimesFrom(start);
         Console.WriteLine("There are {0} prime numbers from {1} to {2}",
                           start, limit);
      }
      catch (NotPrimeException e)
      {
         Console.WriteLine("{0} is not prime", e.NonPrime);
         Console.WriteLine(e);
         Console.WriteLine("--------");
      }

      AppDomain domain = AppDomain.CreateDomain("Domain2");
      PrimeNumberGenerator gen = (PrimeNumberGenerator)domain.CreateInstanceAndUnwrap(
                                        typeof(Example).Assembly.FullName,
                                        "PrimeNumberGenerator", true,
                                        BindingFlags.Default, null,
                                        new object[] { 1000000 }, null, null);
      try
      {
         start = 100;
         Console.WriteLine(gen.GetPrimesFrom(start));
      }
      catch (NotPrimeException e)
      {
         Console.WriteLine("{0} is not prime", e.NonPrime);
         Console.WriteLine(e);
         Console.WriteLine("--------");
      }
   }
}

Imports System.Reflection

Module Example
   Sub Main()
      Dim limit As Integer = 10000000
      Dim primes As New PrimeNumberGenerator(limit)
      Dim start As Integer = 1000001
      Try
         Dim values() As Integer = primes.GetPrimesFrom(start)
         Console.WriteLine("There are {0} prime numbers from {1} to {2}",
                           start, limit)
      Catch e As NotPrimeException
         Console.WriteLine("{0} is not prime", e.NonPrime)
         Console.WriteLine(e)
         Console.WriteLine("--------")
      End Try

      Dim domain As AppDomain = AppDomain.CreateDomain("Domain2")
      Dim gen As PrimeNumberGenerator = domain.CreateInstanceAndUnwrap(
                                        GetType(Example).Assembly.FullName,
                                        "PrimeNumberGenerator", True,
                                        BindingFlags.Default, Nothing,
                                        {1000000}, Nothing, Nothing)
      Try
         start = 100
         Console.WriteLine(gen.GetPrimesFrom(start))
      Catch e As NotPrimeException
         Console.WriteLine("{0} is not prime", e.NonPrime)
         Console.WriteLine(e)
         Console.WriteLine("--------")
      End Try
   End Sub
End Module
' The example displays the following output:
'      1000001 is not prime
'      NotPrimeException: 1000001 is not a prime number.
'         at PrimeNumberGenerator.GetPrimesFrom(Int32 prime)
'         at Example.Main()
'      --------
'      100 is not prime
'      NotPrimeException: 100 is not a prime number.
'         at PrimeNumberGenerator.GetPrimesFrom(Int32 prime)
'         at Example.Main()
'      --------

Windows Runtime and .NET Framework 4.5.1

In .NET for Windows 8.x Store apps for Windows 8, some exception information is typically lost when an exception is propagated through non-.NET Framework stack frames. Starting with the .NET Framework 4.5.1 and Windows 8.1, the common language runtime continues to use the original Exception object that was thrown unless that exception was modified in a non-.NET Framework stack frame.

Constructors

Properties

Methods

Events

Applies to