Exception Handling In C#

Exception Types

There are a number of exception classes provided by C#, all of which inherit from the System.Exception class. Following are some common exception classes.

Exception Class Cause
SystemException A failed run-time check;used as a base class for other.
AccessException Failure to access a type member, such as a method or field.
ArgumentException An argument to a method was invalid.
ArgumentNullException A null argument was passed to a method that doesn't accept it.
ArgumentOutOfRangeException Argument value is out of range.
ArithmeticException Arithmetic over - or underflow has occurred.
ArrayTypeMismatchException Attempt to store the wrong type of object in an array.
BadImageFormatException Image is in the wrong format.
CoreException Base class for exceptions thrown by the runtime.
DivideByZeroException An attempt was made to divide by zero.
FormatException The format of an argument is wrong.
IndexOutOfRangeException An array index is out of bounds.
InvalidCastExpression An attempt was made to cast to an invalid class.
InvalidOperationException A method was called at an invalid time.
MissingMemberException An invalid version of a DLL was accessed.
NotFiniteNumberException A number is not valid.
NotSupportedException Indicates sthat a method is not implemented by a class.
NullReferenceException Attempt to use an unassigned reference.
OutOfMemoryException Not enough memory to continue execution.
StackOverflowException A stack has overflown.

The finally block is used to do all the clean up code. It does not support the error message, but all the code contained in the finally block is executed after the exception is raised. We can use this block along with try-catch and only with catch too.

The finally block is executed even if the error is raised. Control is always passed to the finally block regardless of how the try blocks exits.

This is shown in the following example:

int a, b = 0 ;
Console.WriteLine( "My program starts" ) ;
 a = 10 / b;
catch ( InvalidOperationException e )
 Console.WriteLine ( e ) ;
catch ( DivideByZeroException e)
 Console.WriteLine ( e ) ;
 Console.WriteLine ( "finally" ) ; 
Console.WriteLine ( "Remaining program" ) ; 
The output here is:

My program starts
System.DivideByZeroException: Attempted to divide by zero.
at ConsoleApplication4.Class1.Main(String[] args) in d:\programs\consoleapplication4\class1.cs:line 51
Remaining program

But then what's the difference? We could have written

Console.WriteLine ("finally");

after the catch block, and not write the finally block at all. Writing finally did not make much of a difference. Anyway the code written after catch gets executed. The answer to this is not clear in this program. It will be clear when we see the try-finally and the throw statement.

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About the author

Kamran Shakil Pakistan

I am 22 male. BS(Computer Science), MCSE, Brainbench certifed. Member of .NET Open source, Mono Project. E-author on various websites, including www.dotnetextreme.com, www.csharphelp.com and so...

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