C# - Exception Handling - Adglob Infosystem Pvt Ltd

A C# Exception Handling 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.

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.
throw − A program throws an exception when a problem shows up.

Syntax Of C# Exception Handling

Assuming a block raises an exception, a method catches an exception using a combination of the try and catch keywords. Code within the following −

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
}

You can list down multiple catch statements to catch different types of exceptions in case your try block raises more than one exception in different situations.

Exception Classes in C#

The exception classes in C# are mainly directly or indirectly derived from the System. Exception class. The exception class is 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 exceptions.

The following table provides some of the predefined exception classes derived from the System.SystemException class −

Sr.No.	Exception Class & Description
1	System.IO.IOExceptionHandles I/O errors.
2	System.IndexOutOfRangeExceptionHandles errors are generated when a method refers to an array index out of range.
3	System.ArrayTypeMismatchExceptionHandles errors are generated when the type is mismatched with the array type.
4	System.NullReferenceExceptionHandles errors generated from referencing a null object.
5	System.DivideByZeroExceptionHandles errors are generated from dividing a dividend with zero.
6	System.InvalidCastExceptionHandles errors generated during typecasting.
7	System.OutOfMemoryExceptionHandles errors generated from insufficient free memory.
8	System.StackOverflowExceptionHandles errors generated from stack overflow.

Handling Exceptions

C# provides a structured solution to the exception handling in the form of try and catch blocks.

Following is an example of throwing an exception when dividing by zero condition occurs −

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();
      }
   }
}

The following result −

Exception caught: System.DivideByZeroException: Attempted to divide by zero. 
at ...
Result: 0

Creating User-Defined Exceptions

You can also define your own exception. The following example demonstrates this −

using System;

namespace UserDefinedException {
   class TestTemperature {
      static void Main(string[] args) {
         Temperature temp = new Temperature();
         try {
            temp.showTemp();
         } catch(TempIsZeroException e) {
            Console.WriteLine("TempIsZeroException: {0}", e.Message);
         }
         Console.ReadKey();
      }
   }
}
public class TempIsZeroException: Exception {
   public TempIsZeroException(string message): base(message) {
   }
}
public class Temperature {
   int temperature = 0;
   
   public void showTemp() {
      
      if(temperature == 0) {
         throw (new TempIsZeroException("Zero Temperature found"));
      } else {
         Console.WriteLine("Temperature: {0}", temperature);
      }
   }
}

The following result −

TempIsZeroException: Zero Temperature found

Throwing Objects

You can throw an object if it is either directly or indirectly derived from the System. Exception class. You can use a throw statement in the catch block to throw the present object as −

Catch(Exception e) {
   ...
   Throw e
}

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