Exception Class

Represents errors that occur during application execution.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

[SerializableAttribute]
[ComVisibleAttribute(true)]
[ClassInterfaceAttribute(ClassInterfaceType.None)]
public class Exception : ISerializable, _Exception

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 containing information about the error. Once thrown, an exception is handled by the application or by the default exception handler.

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, respectively. 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. Application code within a try statement is 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 available a text message 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.

  • 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 in the code the error occurs. The stack trace lists all the called methods, and the line numbers in the source file where the calls are made.

Exception Type Categories

Two categories of exceptions exist under the base class Exception:

Exception Class Properties

Exception 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 in the Data property.

The error message string passed to the constructor during the creation of the exception object should be localized, and can be supplied from a resource file using the ResourceManager. For more information on localized resources, see the System.Resources namespace overview and Packaging and Deploying Resources.

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

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

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

Performance Considerations

A significant amount of system resources and execution time are used when you throw or handle an exception. Throw exceptions only to handle truly extraordinary conditions, not to handle predictable events or flow control. For example, your application can reasonably throw an exception if a method argument is invalid because you expect to call your method with valid parameters. An invalid method argument means 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. In such a case, provide a retry mechanism so users can enter valid input.

Throw exceptions only for extraordinary conditions, then catch exceptions in a general purpose exception handler that applies to the majority of your application, not a handler that applies to a specific exception. The rationale for this approach is that most errors can be handled by validation and error handling code in proximity to the error; no exception needs to be thrown or caught. The general purpose exception handler catches truly unexpected exceptions thrown anywhere in the application.

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, then continue processing.

The following code 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 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()

*/

System.Object
  System.Exception
    Microsoft.Build.BuildEngine.InternalLoggerException
    Microsoft.Build.BuildEngine.InvalidProjectFileException
    Microsoft.Build.BuildEngine.InvalidToolsetDefinitionException
    Microsoft.Build.BuildEngine.RemoteErrorException
    Microsoft.Build.Framework.LoggerException
    Microsoft.JScript.CmdLineException
    Microsoft.JScript.ParserException
    Microsoft.ManagementConsole.Advanced.PrimarySnapInDataException
    Microsoft.ManagementConsole.Internal.PrimarySnapInDataException
    Microsoft.VisualBasic.ApplicationServices.CantStartSingleInstanceException
    Microsoft.VisualBasic.ApplicationServices.NoStartupFormException
    Microsoft.VisualBasic.Compatibility.VB6.WebClassContainingClassNotOptional
    Microsoft.VisualBasic.Compatibility.VB6.WebClassCouldNotFindEvent
    Microsoft.VisualBasic.Compatibility.VB6.WebClassNextItemCannotBeCurrentWebItem
    Microsoft.VisualBasic.Compatibility.VB6.WebClassNextItemRespondNotFound
    Microsoft.VisualBasic.Compatibility.VB6.WebClassUserWebClassNameNotOptional
    Microsoft.VisualBasic.Compatibility.VB6.WebClassWebClassFileNameNotOptional
    Microsoft.VisualBasic.Compatibility.VB6.WebClassWebItemNotValid
    Microsoft.VisualBasic.Compatibility.VB6.WebItemAssociatedWebClassNotOptional
    Microsoft.VisualBasic.Compatibility.VB6.WebItemClosingTagNotFound
    Microsoft.VisualBasic.Compatibility.VB6.WebItemCouldNotLoadEmbeddedResource
    Microsoft.VisualBasic.Compatibility.VB6.WebItemCouldNotLoadTemplateFile
    Microsoft.VisualBasic.Compatibility.VB6.WebItemNameNotOptional
    Microsoft.VisualBasic.Compatibility.VB6.WebItemNoTemplateSpecified
    Microsoft.VisualBasic.Compatibility.VB6.WebItemTooManyNestedTags
    Microsoft.VisualBasic.Compatibility.VB6.WebItemUnexpectedErrorReadingTemplateFile
    Microsoft.VisualBasic.CompilerServices.IncompleteInitialization
    Microsoft.VisualBasic.CompilerServices.InternalErrorException
    Microsoft.VisualBasic.FileIO.MalformedLineException
    System.AddIn.Hosting.AddInSegmentDirectoryNotFoundException
    System.AddIn.Hosting.InvalidPipelineStoreException
    System.ApplicationException
    System.ComponentModel.Design.ExceptionCollection
    System.Configuration.Provider.ProviderException
    System.Configuration.SettingsPropertyIsReadOnlyException
    System.Configuration.SettingsPropertyNotFoundException
    System.Configuration.SettingsPropertyWrongTypeException
    System.Data.Linq.ChangeConflictException
    System.Diagnostics.Eventing.Reader.EventLogException
    System.DirectoryServices.ActiveDirectory.ActiveDirectoryObjectExistsException
    System.DirectoryServices.ActiveDirectory.ActiveDirectoryObjectNotFoundException
    System.DirectoryServices.ActiveDirectory.ActiveDirectoryOperationException
    System.DirectoryServices.ActiveDirectory.ActiveDirectoryServerDownException
    System.DirectoryServices.Protocols.DirectoryException
    System.IdentityModel.Selectors.CardSpaceException
    System.IdentityModel.Selectors.IdentityValidationException
    System.IdentityModel.Selectors.PolicyValidationException
    System.IdentityModel.Selectors.ServiceBusyException
    System.IdentityModel.Selectors.ServiceNotStartedException
    System.IdentityModel.Selectors.StsCommunicationException
    System.IdentityModel.Selectors.UnsupportedPolicyOptionsException
    System.IdentityModel.Selectors.UntrustedRecipientException
    System.IdentityModel.Selectors.UserCancellationException
    System.InvalidTimeZoneException
    System.IO.IsolatedStorage.IsolatedStorageException
    System.IO.Log.SequenceFullException
    System.Management.Instrumentation.InstrumentationBaseException
    System.Management.Instrumentation.WmiProviderInstallationException
    System.Net.Mail.SmtpException
    System.Net.PeerToPeer.PeerToPeerException
    System.Runtime.CompilerServices.RuntimeWrappedException
    System.Runtime.Remoting.MetadataServices.SUDSGeneratorException
    System.Runtime.Remoting.MetadataServices.SUDSParserException
    System.Runtime.Serialization.InvalidDataContractException
    System.Security.RightsManagement.RightsManagementException
    System.ServiceModel.Channels.InvalidChannelBindingException
    System.SystemException
    System.Threading.LockRecursionException
    System.TimeZoneNotFoundException
    System.Web.Query.Dynamic.ParseException
    System.Web.Security.MembershipCreateUserException
    System.Web.Security.MembershipPasswordException
    System.Web.UI.ViewStateException
    System.Web.UI.WebControls.LinqDataSourceValidationException
    System.Windows.Automation.NoClickablePointException
    System.Windows.Automation.ProxyAssemblyNotLoadedException
    System.Windows.Controls.PrintDialogException
    System.Windows.Forms.AxHost.InvalidActiveXStateException
    System.Windows.Xps.XpsException
    System.Windows.Xps.XpsWriterException
    System.Workflow.Activities.Rules.RuleException
    System.Workflow.ComponentModel.Compiler.WorkflowValidationFailedException
    System.Workflow.ComponentModel.Serialization.WorkflowMarkupSerializationException
    System.Workflow.ComponentModel.WorkflowTerminatedException
    System.Workflow.Runtime.WorkflowOwnershipException

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0
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