System Namespace   Exception Class

---

Returns the Exception instance that caused the current exception.

[ VB ]
<Serializable>
<ClassInterface ( ClassInterfaceType.AutoDual ) >
Public ReadOnly Property InnerException As Exception

[ C# ]
[ Serializable ]
[ ClassInterface ( ClassInterfaceType.AutoDual ) ]
public Exception InnerException {get;}

[ C++ ]
[ Serializable ]
[ ClassInterface ( ClassInterfaceType.AutoDual ) ]
public: __property Exception* get_InnerException ( );

[ JScript ]
public Serializable
   ClassInterface ( ClassInterfaceType.AutoDual )
function get InnerException ( ) : Exception;

An instance of Exception that describes the error that caused the current exception. The InnerException property returns the same value as was passed into the constructor, or a null reference ( Nothing in Visual Basic ) if the inner exception value was not supplied to the constructor. This property is read-only.

When an exception X is thrown as a direct result of a previous exception Y, the InnerException property of X should contain a reference to Y.

Use the InnerException property to obtain the set of exceptions that led to the current exception.

You can create a new exception that catches an earlier exception. The code that handles the second exception can make use of the additional information from the earlier exception to handle the error more appropriately.

Suppose that there is a function that reads a file and formats the data from that file. In this example, as the code tries to read the file, an IOException is thrown. The function catches the IOException and throws a FileNotFoundException. The IOException could be saved in the InnerException property of the FileNotFoundException, enabling the code that catches the FileNotFoundException to examine what causes the initial error.

The InnerException property, which holds a reference to the inner exception, is set upon initialization of the exception object.

The following example demonstrates throwing and catching an exception that references an inner exception.

[ VB ]
Imports System

Public Class MyAppException
   Inherits ApplicationException

   Public Sub New ( message As [ String ] )
      MyBase.New ( message )
   End Sub 'New

   Public Sub New ( message As [ String ], inner As Exception )
      MyBase.New ( message, inner )
   End Sub 'New
End Class 'MyAppException

Public Class ExceptExample

   Public Sub ThrowInner ( )
      Throw New MyAppException ( "ExceptExample inner exception" )
   End Sub 'ThrowInner

   Public Sub CatchInner ( )
      Try
         Me.ThrowInner ( )
      Catch e As Exception
         Throw New MyAppException ( "Error caused by trying ThrowInner.", e )
      End Try
   End Sub 'CatchInner
End Class 'ExceptExample

Public Class Test

   Public Shared Sub Main ( )
      Dim testInstance As New ExceptExample ( )
      Try
         testInstance.CatchInner ( )
      Catch e As Exception
         Response.Write ( "In Main catch block. Caught: {0}", e.Message )
         Response.Write ( "Inner Exception is {0}", e.InnerException )
      End Try
   End Sub 'Main
End Class 'Test

[ C# ]
using System;
public class MyAppException:ApplicationException
{
   public MyAppException ( String message ) : base ( message )
   {}
   public MyAppException ( String message, Exception inner ) : base ( message,inner ) {}
   }
public class ExceptExample
{
   public void ThrowInner ( )
   {
   throw new MyAppException ( "ExceptExample inner exception" );
   }
   public void CatchInner ( )
   {
      try
      {
      this.ThrowInner ( );
      }
         catch ( Exception e )
         {
         throw new MyAppException ( "Error caused by trying ThrowInner.",e );
         }
      }
   }
public class Test
{
   public static void Main ( )
   {
   ExceptExample testInstance = new ExceptExample ( );
      try
      {
      testInstance.CatchInner ( );
      }
         catch ( Exception e )
         {
         Response.Write ( "In Main catch block. Caught: {0}", e.Message );
         Response.Write ( "Inner Exception is {0}",e.InnerException );
         }
      }
}

[ VB, C# ] This code has the following output:

[ VB, C# ] In Main

catch block. Caught: Error caused by trying ThrowInner. Inner Exception is

MyAppException: ExceptExample inner exception at ExceptExample.ThrowInner ( ) at

ExceptExample.CatchInner ( )

Exception Members

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