Exception Handlin
An exception is a problem that arises during the execution of a
program. A C# exception is a response to an exceptional circumstance that
arises while a program is running, such as an attempt to divide by zero.
Exceptions provide a way to transfer control from one part of a
program to another. C# exception handling is built upon four keywords: try, catch, finally, and throw.
·
try: A try block identifies a
block of code for which particular exceptions is activated. It is followed by
one or more catch blocks.
·
catch: A program catches an
exception with an exception handler at the place in a program where you want to
handle the problem. The catch keyword indicates the catching of an exception.
·
finally: The finally block is
used to execute a given set of statements, whether an exception is thrown or
not thrown. For example, if you open a file, it must be closed whether an
exception is raised or not.
·
throw: A program throws an
exception when a problem shows up. This is done using a throw keyword.
·
try
·
{
·
//
statements causing exception
·
}
·
catch( ExceptionName e1 )
·
{
·
//
error handling code
·
}
·
catch( ExceptionName e2 )
·
{
·
//
error handling code
·
}
·
catch( ExceptionName eN )
·
{
·
//
error handling code
·
}
·
finally
·
{
·
//
statements to be executed
·
}
Exception Classes in C#
C#
exceptions are represented by classes. The exception classes in C# are mainly
directly or indirectly derived from the System.Exception class.
Some of the exception classes derived from the System.Exception class are
the System.ApplicationException and System.SystemException classes.
The System.ApplicationException class
supports exceptions generated by application programs. Hence the exceptions
defined by the programmers should derive from this class.
The System.SystemException class
is the base class for all predefined system exception.
The
following table provides some of the predefined exception classes derived from
the Sytem.SystemException class:
|
Exception
Class
|
Description
|
|
System.IO.IOException
|
Handles
I/O errors.
|
|
System.IndexOutOfRangeException
|
Handles
errors generated when a method refers to an array index out of range.
|
|
System.ArrayTypeMismatchException
|
Handles
errors generated when type is mismatched with the array type.
|
|
System.NullReferenceException
|
Handles
errors generated from deferencing a null object.
|
|
System.DivideByZeroException
|
Handles
errors generated from dividing a dividend with zero.
|
|
System.InvalidCastException
|
Handles
errors generated during typecasting.
|
|
System.OutOfMemoryException
|
Handles
errors generated from insufficient free memory.
|
|
System.StackOverflowException
|
Handles
errors generated from stack overflow.
|
using System;
namespace ErrorHandlingApplication
{
class DivNumbers
{
int result;
DivNumbers()
{
result = 0;
}
public void division(int num1, int num2)
{
try
{
result = num1 / num2;
}
catch (DivideByZeroException e)
{
Console.WriteLine("Exception caught: {0}", e);
}
finally
{
Console.WriteLine("Result: {0}", result);
}
}
static void Main(string[] args)
{
DivNumbers d = new DivNumbers();
d.division(25, 0);
Console.ReadKey();
}
}
}
When the above code is compiled and executed, it produces the
following result:
Exception caught: System.DivideByZeroException: Attempted to divide by zero.
at ...
Result: 0
Throws
public class ThrowTest2
{
static int GetNumber(int index)
{
int[] nums = { 300, 600, 900 };
if (index > nums.Length)
{
throw new IndexOutOfRangeException();
}
return nums[index];
}
static void Main()
{
int result = GetNumber(3);
}
}
/*
Output:
The System.IndexOutOfRangeException exception occurs.
*/
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