Exception Class
Represents errors that occur during application execution.
Assembly: mscorlib (in mscorlib.dll)
The Exception type exposes the following members.
| Name | Description | |
|---|---|---|
![]() ![]() ![]() | Exception() | Initializes a new instance of the Exception class. |
![]() ![]() ![]() | Exception(String) | Initializes a new instance of the Exception class with a specified error message. |
![]() | Exception(SerializationInfo, StreamingContext) | Initializes a new instance of the Exception class with serialized data. |
![]() ![]() ![]() | Exception(String, Exception) | Initializes a new instance of the Exception class with a specified error message and a reference to the inner exception that is the cause of this exception. |
| Name | Description | |
|---|---|---|
![]() | Data | Gets a collection of key/value pairs that provide additional user-defined information about the exception. |
![]() | HelpLink | Gets or sets a link to the help file associated with this exception. |
![]() ![]() ![]() | HResult | Gets or sets HRESULT, a coded numerical value that is assigned to a specific exception. |
![]() ![]() ![]() | InnerException | Gets the Exception instance that caused the current exception. |
![]() ![]() ![]() | Message | Gets a message that describes the current exception. |
![]() | Source | Gets or sets the name of the application or the object that causes the error. |
![]() ![]() ![]() | StackTrace | Gets a string representation of the immediate frames on the call stack. |
![]() | TargetSite | Gets the method that throws the current exception. |
| Name | Description | |
|---|---|---|
![]() ![]() ![]() | Equals(Object) | Determines whether the specified Object is equal to the current Object. (Inherited from Object.) |
![]() ![]() ![]() | Finalize | Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.) |
![]() ![]() ![]() | GetBaseException | When overridden in a derived class, returns the Exception that is the root cause of one or more subsequent exceptions. |
![]() ![]() ![]() | GetHashCode | Serves as a hash function for a particular type. (Inherited from Object.) |
![]() | GetObjectData | When overridden in a derived class, sets the SerializationInfo with information about the exception. |
![]() ![]() ![]() | GetType | Gets the runtime type of the current instance. In XNA Framework 3.0, this member is inherited from Object::GetType(). In Portable Class Library Portable Class Library, this member is inherited from Object::GetType(). |
![]() ![]() ![]() | MemberwiseClone | Creates a shallow copy of the current Object. (Inherited from Object.) |
![]() ![]() ![]() | ToString | Creates and returns a string representation of the current exception. (Overrides Object::ToString().) |
| Name | Description | |
|---|---|---|
![]() | SerializeObjectState | Occurs when an exception is serialized to create an exception state object that contains serialized data about the 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:
The pre-defined common language runtime exception classes derived from SystemException.
The user-defined application exception classes derived from ApplicationException.
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 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() */
Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
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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
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System.DirectoryServices.Protocols::DirectoryException
System.IdentityModel.Selectors::CardSpaceException
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