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==A Closer Look at Exception==

<OL><LI>Message property contains a string that describes the nature of the error.</LI><LI>StackTrace property contains a string that contains the stack of calls that lead to the exception.</LI><LI>TargetSite property obtains an object that specifies the method that generated the exception.</LI></OL>
System.Exception also defines several methods.
<OL><LI>ToString() returns a string that describes the exception.</LI><LI>Exception defines four constructors.</LI></OL>
The most commonly used are shown here:

<source lang="csharp">Exception()
Exception(string str)</source>

==An unhandled exception==

<source lang="csharp">using System;
class MainClass
{
public static void Main()
{
int[] myArray = new int[2];
Console.WriteLine("Attempting to access an invalid array element");
myArray[2] = 1;
}
}</source>
<pre class=codeResult>Attempting to access an invalid array element
Unhandled Exception: System.IndexOutOfRangeException: Index was outside the bounds of the array.
at MainClass.Main()</pre>

==Commonly Used Exceptions Defined Within the System Namespace ==

Exception
Meaning
ArrayTypeMismatchException
Type is incompatible with the type of the array.
DivideByZeroException
Division by zero attempted.
IndexOutOfRangeException
Array index is out of bounds.
InvalidCastException
A runtime cast is invalid.
OutOfMemoryException
Insufficient free memory exists.
OverflowException
An arithmetic overflow occurred.
NullReferenceException
An attempt was made to operate on a null reference�that is, a reference that does not refer to an object.
StackOverflowException
The stack was Overflow.
As a general rule, exceptions defined by you should be derived from ApplicationException since this is the
hierarchy reserved for application- related exceptions.

==Exception propagation with methods==

<source lang="csharp">using System;
class MainClass
{
public static void Main()
{
Console.WriteLine("Calling AccessInvalidArrayElement()");
AccessInvalidArrayElement();
try
{
Console.WriteLine("Calling DivideByZero()");
DivideByZero();
} catch (DivideByZeroException e) {
Console.WriteLine("Handling an IndexOutOfRangeException");
Console.WriteLine("Message = " + e.Message);
Console.WriteLine("StackTrace = " + e.StackTrace);
}
}
public static void AccessInvalidArrayElement()
{
int[] myArray = new int[2];
try
{
Console.WriteLine("Attempting to access an invalid array element");
myArray[20] = 1;
}
catch (IndexOutOfRangeException e)
{
Console.WriteLine("Handling an IndexOutOfRangeException");
Console.WriteLine("Message = " + e.Message);
Console.WriteLine("StackTrace = " + e.StackTrace);
}
}
public static void DivideByZero()
{
int zero = 0;
Console.WriteLine("Attempting division by zero");
int myInt = 1 / zero;
}
}</source>
<pre class=codeResult>Calling AccessInvalidArrayElement()
Attempting to access an invalid array element
Handling an IndexOutOfRangeException
Message = Index was outside the bounds of the array.
StackTrace = at MainClass.AccessInvalidArrayElement()
Calling DivideByZero()
Attempting division by zero
Handling an IndexOutOfRangeException
Message = Attempted to divide by zero.
StackTrace = at MainClass.Main()</pre>

==Handling a possible exception.==

<source lang="csharp">using System;
class MainClass {
public static int AnExceptionFunction(int value) {
if (value == 0) // Can"t divide by zero
throw new DivideByZeroException("Divide By 0 error!");
int x = 20 / value;
return x;
}
public static void Main() {
int value = 0;
try {
value = AnExceptionFunction(10); // This works ok
Console.WriteLine("Value = {0}", value);
AnExceptionFunction(0); // This doesn"t
Console.WriteLine("Value = {0}", value);
} catch (Exception e) {
Console.WriteLine("Caught an exception {0}. Continuing", e);
}
Console.WriteLine("Done");
}
}</source>

==The Exception Hierarchy==

An exception is an error that occurs at runtime.

<source lang="csharp">using System;
class MainClass{

public static void Main(){
int Zero = 0;
try {
int j = 22 / Zero;
} catch (DivideByZeroException e) // catch a specific exception
{
Console.WriteLine("DivideByZero {0}", e);
} catch (Exception e)// catch any remaining exceptions
{
Console.WriteLine("Exception {0}", e);
}
}
}</source>
<pre class=codeResult>DivideByZero System.DivideByZeroException: Attempted to divide by zero.
at MainClass.Main()</pre>

==The System.Exception Class==

<OL><LI>In C#, exceptions are represented by classes.</LI><LI>All exception classes must be derived from the built-in exception class System.Exception.</LI><LI>SystemException class and ApplicationException class are derived from System.Exception.</LI><LI>SystemException support exceptions generated by the C# runtime system (that is, the Common Language Runtime)</LI><LI>ApplicationException support exceptions generated by application programs.</LI><LI>SystemException and ApplicationException add nothing to Exception.</LI><LI>SystemException and ApplicationException define the tops of two different exception hierarchies.</LI></OL>
1.17.Exception
1.17.1.
<A href="/Tutorial/CSharp/0020__Language-Basics/TheExceptionHierarchy.htm">The Exception Hierarchy</a>
1.17.2.
The System.Exception Class
1.17.3.
<A href="/Tutorial/CSharp/0020__Language-Basics/ACloserLookatException.htm">A Closer Look at Exception</a>
1.17.4.
<A href="/Tutorial/CSharp/0020__Language-Basics/UsingExceptionmembers.htm">Using Exception members</a>
1.17.5.
<A href="/Tutorial/CSharp/0020__Language-Basics/Exceptionpropagationwithmethods.htm">Exception propagation with methods</a>
1.17.6.
<A href="/Tutorial/CSharp/0020__Language-Basics/Anunhandledexception.htm">An unhandled exception</a>
1.17.7.
<A href="/Tutorial/CSharp/0020__Language-Basics/CommonlyUsedExceptionsDefinedWithintheSystemNamespace.htm">Commonly Used Exceptions Defined Within the System Namespace </a>
1.17.8.
<A href="/Tutorial/CSharp/0020__Language-Basics/Handlingapossibleexception.htm">Handling a possible exception.</a>

==Using Exception members==

<source lang="csharp">using System;

class MainClass {
public static void Main() {

try {
int[] nums = new int[4];

Console.WriteLine("Before exception is generated.");

// Generate an index out-of-bounds exception.
for(int i=0; i < 10; i++) {
nums[i] = i;
}
}
catch (IndexOutOfRangeException exc) {
Console.WriteLine("Standard message is: ");
Console.WriteLine(exc); // calls ToString()
Console.WriteLine("Stack trace: " + exc.StackTrace);
Console.WriteLine("Message: " + exc.Message);
Console.WriteLine("TargetSite: " + exc.TargetSite);
Console.WriteLine("Class defining member: {0}", exc.TargetSite.DeclaringType);
Console.WriteLine("Member type: {0}", exc.TargetSite.MemberType);
Console.WriteLine("Source: {0}", exc.Source);
Console.WriteLine("Help Link: {0}", exc.HelpLink);

}
Console.WriteLine("After catch statement.");
}
}</source>
<pre class=codeResult>Before exception is generated.
Standard message is:
System.IndexOutOfRangeException: Index was outside the bounds of the array.
at MainClass.Main()
Stack trace: at MainClass.Main()
Message: Index was outside the bounds of the array.
TargetSite: Void Main()
Class defining member: MainClass
Member type: Method
Source: main
Help Link:
After catch statement.</pre>

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