Csharp/CSharp Tutorial/Language Basics/Exception Throw

Creating and throwing an exception object

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

 public static void Main()
 {
   try
   {
     Exception myException = new Exception("myException");
     myException.HelpLink = "See the Readme.txt file";
     myException.Source = "My Program";
     throw myException;
   }
   catch (Exception e)
   {
     Console.WriteLine("HelpLink = " + e.HelpLink);
     Console.WriteLine("Message = " + e.Message);
     Console.WriteLine("Source = " + e.Source);
     Console.WriteLine("StackTrace = " + e.StackTrace);
     Console.WriteLine("TargetSite = " + e.TargetSite);
   }
 }

}</source>

HelpLink = See the Readme.txt file
Message = myException
Source = My Program
StackTrace =    at MainClass.Main()
TargetSite = Void Main()

Manually throw an exception.

The general form is:

<source lang="csharp">throw exceptOb;</source>

Rethrow an exception

<source lang="csharp">using System;

class MainClass {

 public static void Main() { 
   try { 
     genException(); 
   } 
   catch(IndexOutOfRangeException) { 
     // recatch exception 
    Console.WriteLine("Fatal error -- " + 
                      "program terminated."); 
   } 
 }
 public static void genException() { 
   int[] numer = { 4, 8}; 
   int d = 0; 

   for(int i=0; i<10; i++) { 
     try { 
       Console.WriteLine(numer[i] + " / " + 
                         numer[i] + " is " + 
                         numer[i]/d); 
     } 
     catch (DivideByZeroException) { 
       // catch the exception 
       Console.WriteLine("Can"t divide by Zero!"); 
     } 
     catch (IndexOutOfRangeException) { 
       // catch the exception 
       Console.WriteLine("No matching element found."); 
       throw; // rethrow the exception 
     } 
   } 
 }   
  

}</source>

Can"t divide by Zero!
Can"t divide by Zero!
No matching element found.
Fatal error -- program terminated.

Throw Exception from a function

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

   static void AFunction()
   {
       int Zero = 0;
       int j = 22 / Zero;
   }
   public static void Main()
   {
       try
       {
           Console.WriteLine("efore Function");
           AFunction();
       }
       catch (DivideByZeroException e)
       {
           Console.WriteLine("DivideByZero {0}", e);
       }
   }

}</source>

efore Function
DivideByZero System.DivideByZeroException: Attempted to divide by zero.
   at MainClass.Main()

Throw Exception in finally statement

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

   static void Main() {
       try {
           try {
               ArrayList list = new ArrayList();
               list.Add( 1 );
               Console.WriteLine( "Item 10 = {0}", list[10] );
           }
           finally {
               Console.WriteLine( "Cleaning up..." );
               throw new Exception( "I like to throw" );
           }
       }
       catch( ArgumentOutOfRangeException ) {
           Console.WriteLine( "Oops!  Argument out of range!" );
       }
       catch {
           Console.WriteLine( "Done" );
       }
   }

}</source>

Cleaning up...
Done

Wrap exception in another one, adding additional context

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

   public void DoAverage()
   {
       try
       {
           int count = 0;
           int average = 10 / count;
       }
       catch (DivideByZeroException e)
       {
           
           throw (new DivideByZeroException(
           "Count is zero in DoAverage()", e));
       }
   }

} public class MainClass {

   public static void Main()
   {
       MyClass my = new MyClass();
       try
       {
           my.DoAverage();
       }
       catch (Exception e)
       {
           Console.WriteLine("Exception: {0}", e);
       }
   }

}</source>

Exception: System.DivideByZeroException: Count is zero in DoAverage() ---> System.DivideByZeroExcept
ion: Attempted to divide by zero.
   at MyClass.DoAverage()
   --- End of inner exception stack trace ---
   at MyClass.DoAverage()
   at MainClass.Main()