Csharp/CSharp Tutorial/Language Basics/Exception Throw

Creating and throwing an exception object

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);
    }
  }
}

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:

throw exceptOb;

Rethrow an exception

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 
      } 
    } 
  }   
   
}

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

Throw Exception from a function

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);
        }
    }
}

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

Throw Exception in finally statement

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" );
        }
    }
}

Cleaning up...
Done

Wrap exception in another one, adding additional context

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);
        }
    }
}

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()