Exception Handling Basics in C#

An exception is any uncommon condition arising during execution of a program. There might be several conditions when an exception is encountered in a program but at most basic level examples of exceptions include file not found exception, dividing a number by 0, inputting a wrong data type values etc

It is necessary to handle exceptions otherwise an end user will not feel at home with the application and it is a sign of poor problem understanding. Just for example, if there is a program which accepts a string “thinkdigital” and converts it to uppercase “THINKDIGITAL” and vice a versa then there must be a facility which handles an event when a user enters a non-string input which cannot be understood by the program. This is just an example to make any layman understand about the logic of exception

In .net framework, we have System.Exception class which provides all possible exception handling facility in c#.

Any piece of code which can trigger an exception goes under the ‘try’ block, once an exception occurs, the control moves to the ‘catch’ block and handles the exception. A try block can have number of catch block depending upon different types of exceptions occurring during an operation. But always the base catch block executes first and if required child catch blocks are executed.  There is a ‘finally’ block which is optionally used for performing maintenance tasks like freeing memory, closing file stream connections etc.


// Illustration code

using System;
using System.IO; //required for file operations


class ExceptionExampleProgram
{
    public static void Main()
    {
        StreamReader streamReader = null;
        try //code which may trigger an exception comes under the try block
        {
            streamReader = new StreamReader("C:\\file\\info.txt"); //reads the content of the file specified
            Console.WriteLine(streamReader.ReadToEnd());
            streamReader.Close();

        }
        catch (FileNotFoundException Trial) // handles the exception using predefined properties in exception class or user defined message
        {

            //Console.WriteLine(FileNotFound.Message); // printing message using system defined 'Message' property
            Console.WriteLine("This program can not find the file specified {0}, Please check again", Trial.FileName); // printing user defined message to make things more clear
         
        }
        finally // to perform clean up tasks like closing connections and release memory for efficiency
        {
            if (streamReader !=null) // required as if stream reader is null then it cant be closed
            {
            streamReader.Close();
            }
            Console.WriteLine("Stream reader now closed, so is this article :P");
            Console.ReadLine();
        }
    }
}

Screenshots // click to open a higher resolution version

/* Normal Execution */

/* File Not Found Exception Handling */

/* Another type of exception which can occur if directory path is altered, 

another catch block is required for this */