Csharp/C Sharp/Language Basics/Exception Class

calls GetBaseException and outputs the error message of the initial exception.

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

   public static void Main() {
       try {
           MethodA();
       } catch (Exception except) {
           Exception original = except.GetBaseException();
           Console.WriteLine(original.Message);
       }
   }
   public static void MethodA() {
       try {
           MethodB();
       } catch (Exception except) {
           throw new ApplicationException("Inner Exception", except);
       }
   }
   public static void MethodB() {
       throw new ApplicationException("Innermost Exception");
   }

}

</source>

Demonstrates defining and using a custom exception class

<source lang="csharp"> /* C# Programming Tips & Techniques by Charles Wright, Kris Jamsa Publisher: Osborne/McGraw-Hill (December 28, 2001) ISBN: 0072193794

• /

// // CustExcp.cs -- Demonstrates defining and using a custom exception class // // Compile this program with the following command line: // C:>csc CustExcp.cs // namespace nsCustomException {

   using System;
   using System.IO;
   
   public class CustExcpclsMain
   {
       static public void Main (string [] args)
       {
           if (args.Length < 2)
           {
               Console.WriteLine ("usage: CustExcp FileName String");
               return;
           }
           try
           {
               ReadFile (args[0], args[1]);
               Console.WriteLine (args[1] + " was not found in " + args[0]);
           }

// Custom exception thrown. Display the information.

           catch (clsException e)
           {
               Console.WriteLine ("string {0} first occurs in {1} at Line {2}, Column {3}",
                                  args[1], args[0], e.Line, e.Column);
               Console.WriteLine (e.Found);
               return;
           }

// Check for other possible exceptions.

           catch (ArgumentException)
           {
               Console.WriteLine ("The file name " + args [0] +
                         " is empty or contains an invalid character");
           }
           catch (FileNotFoundException)
           {
               Console.WriteLine ("The file name " + args [0] +
                                  " cannot be found");
           }
           catch (DirectoryNotFoundException)
           {
               Console.WriteLine ("The path for " + args [0] +
                                  " is invalid");
           }
           catch (Exception e)
           {
               Console.WriteLine (e);
           }
       }
       static public void ReadFile (string FileName, string Find)
       {
           FileStream strm;
           StreamReader reader;
           try
           {
               strm = new FileStream (FileName, FileMode.Open);
               reader = new StreamReader (strm);
               int Line = 0;
               while (reader.Peek () >= 0)
               {
                   ++Line;
                   string str = reader.ReadLine ();
                   int index = str.IndexOf (Find);
                   if (index >= 0)
                   {
                       reader.Close ();
                       strm.Close ();
                       clsException ex = new clsException ();
                       ex.Line = Line;
                       ex.Column = index + 1;
                       ex.Found = str;
                       throw (ex);
                   }
               }
               reader.Close ();
               strm.Close ();
               return;
           }
           catch (IOException e)
           {

// If file not found, go back and get another name

               if (e is FileNotFoundException)
                   throw (e);

// Code here to handle other IOException classes

               Console.WriteLine (e.Message);
               throw (new IOException());
           }
      }
   }

// Define a class derived from Exception

   class clsException : Exception
   {
       public int Line = 0;
       public int Column = 0;
       public string Found = null;
   }

}

      </source>

Derived exceptions must appear before base class exceptions

<source lang="csharp"> /* C#: The Complete Reference by Herbert Schildt Publisher: Osborne/McGraw-Hill (March 8, 2002) ISBN: 0072134852

• /

// Derived exceptions must appear before base class exceptions.

using System;

// Create an exception. class ExceptA : ApplicationException {

 public ExceptA() : base() { } 
 public ExceptA(string str) : base(str) { } 

 public override string ToString() { 
   return Message; 
 } 

}

// Create an exception derived from ExceptA class ExceptB : ExceptA {

 public ExceptB() : base() { } 
 public ExceptB(string str) : base(str) { } 

 public override string ToString() { 
   return Message;  
 } 

}

public class OrderMatters {

 public static void Main() { 
   for(int x = 0; x < 3; x++) { 
     try { 
       if(x==0) throw new ExceptA("Caught an ExceptA exception"); 
       else if(x==1) throw new ExceptB("Caught an ExceptB exception"); 
       else throw new Exception(); 
     } 
     catch (ExceptB exc) { 
       // catch the exception 
       Console.WriteLine(exc); 
     } 
     catch (ExceptA exc) { 
       // catch the exception 
       Console.WriteLine(exc); 
     } 
     catch (Exception exc) { 
       Console.WriteLine(exc); 
     } 
   } 
 } 

}

      </source>

Exception handle with your own exception class

<source lang="csharp"> /* Learning C# by Jesse Liberty Publisher: O"Reilly ISBN: 0596003765

• /

using System;
namespace ExceptionHandling
{
    // custom exception class
    class MyCustomException :
        System.ApplicationException
    {
        public MyCustomException(string message):
            base(message) // pass the message up to the base class
        {
        }
    }
   public class TesterExceptionHandling
   {
      public void Run()
      {
          try
          {
              Console.WriteLine("Open file here");
              double a = 0;
              double b = 5;
              Console.WriteLine ("{0} / {1} = {2}",
                  a, b, DoDivide(a,b));
              Console.WriteLine (
                  "This line may or may not print");
          }
              // most derived exception type first
          catch (System.DivideByZeroException e)
          {
              Console.WriteLine(
                  "\nDivideByZeroException! Msg: {0}",
                  e.Message);
              Console.WriteLine(
                  "\nHelpLink: {0}\n", e.HelpLink);
          }
          // catch custom exception
          catch (MyCustomException e)
          {
              Console.WriteLine(
                  "\nMyCustomException! Msg: {0}",
                  e.Message);
              Console.WriteLine(
                  "\nHelpLink: {0}\n", e.HelpLink);
          }
          catch     // catch any uncaught exceptions
          {
              Console.WriteLine(
                  "Unknown exception caught");
          }
          finally
          {
              Console.WriteLine ("Close file here.");
          }
      }
       // do the division if legal
       public double DoDivide(double a, double b)
       {
           if (b == 0)
           {
               DivideByZeroException e =
                   new DivideByZeroException();
               e.HelpLink=
                   "http://www.libertyassociates.ru";
               throw e;
           }
           if (a == 0)
           {
               // create a custom exception instance
               MyCustomException e =
                   new MyCustomException(
                   "Can"t have zero divisor");
               e.HelpLink =
                   "http://www.libertyassociates.ru/NoZeroDivisor.htm";
               throw e;
           }
           return a/b;
       }
       static void Main()
       {
           Console.WriteLine("Enter Main...");
           TesterExceptionHandling t = new TesterExceptionHandling();
           t.Run();
           Console.WriteLine("Exit Main...");
       }
   }
}
          
      </source>

Exception Handling: The Exception Hierarchy 1

<source lang="csharp"> using System;

public class ExceptionHierarchy {

   static int Zero = 0;
   public static void Main()
   {
       try
       {
           int j = 22 / Zero;
       }
       // catch a specific exception
       catch (DivideByZeroException e)
       {
           Console.WriteLine("DivideByZero {0}", e);
       }
       // catch any remaining exceptions
       catch (Exception e)
       {
           Console.WriteLine("Exception {0}", e);
       }
   }

}

      </source>

Exception Handling: The Exception Hierarchy 2

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

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

}

      </source>

Exception Handling: The Exception Hierarchy 3

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

   static int Zero = 0;
   static void AFunction()
   {
       try
       {
           int j = 22 / Zero;
       }
      // this exception doesn"t match
       catch (ArgumentOutOfRangeException e)
       {
           Console.WriteLine("OutOfRangeException: {0}", e);
       }
       Console.WriteLine("In AFunction()");
   }
   public static void Main()
   {
       try
       {
           AFunction();
       }
       // this exception doesn"t match
       catch (ArgumentException e)
       {
           Console.WriteLine("ArgumentException {0}", e);
       }
   }

}

      </source>

Exception Handling User-Defined Exception Classes

<source lang="csharp"> /* A Programmer"s Introduction to C# (Second Edition) by Eric Gunnerson Publisher: Apress L.P. ISBN: 1-893115-62-3

• /

// 04 - Exception Handling\User-Defined Exception Classes // copyright 2000 Eric Gunnerson using System; public class UserDefinedExceptionClasses {

   public static void Main()
   {
       Summer summer = new Summer();
       try
       {
           summer.DoAverage();
       }
       catch (CountIsZeroException e)
       {
           Console.WriteLine("CountIsZeroException: {0}", e);
       }
   }

} public class CountIsZeroException: ApplicationException {

   public CountIsZeroException()
   {
   }
   public CountIsZeroException(string message)
   : base(message)
   {
   }
   public CountIsZeroException(string message, Exception inner)
   : base(message, inner)
   {
   }

} public class Summer {

   int    sum = 0;
   int    count = 0;
   float    average;
   public void DoAverage()
   {
       if (count == 0)
       throw(new CountIsZeroException("Zero count in DoAverage"));
       else
       average = sum / count;
   }

}

      </source>

illustrates a custom exception

<source lang="csharp"> /* Mastering Visual C# .NET by Jason Price, Mike Gunderloy Publisher: Sybex; ISBN: 0782129110

• /

/*

 Example13_9.cs illustrates a custom exception

• /

using System;

// declare the CustomException class class CustomException : ApplicationException {

 public CustomException(string Message) : base(Message)
 {
   // set the HelpLink and Source properties
   this.HelpLink = "See the Readme.txt file";
   this.Source = "My Example13_9 Program";
 }

}

public class Example13_9 {

 public static void Main()
 {
   try
   {
     // throw a new CustomException object
     Console.WriteLine("Throwing a new CustomException object");
     throw new CustomException("My CustomException message");
   }
   catch (CustomException e)
   {
     // display the CustomException object"s properties
     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>

illustrates the use of a System.Exception object

<source lang="csharp"> /* Mastering Visual C# .NET by Jason Price, Mike Gunderloy Publisher: Sybex; ISBN: 0782129110

• /

/*

 Example13_2.cs illustrates the use of a
 System.Exception object

• /

using System; public class Example13_2 {

 public static void Main()
 {
   try
   {
     int zero = 0;
     Console.WriteLine("In try block: attempting division by zero");
     int myInt = 1 / zero;  // throws the exception
   }
   catch (System.Exception myException)
   {
     // display the exception object"s properties
     Console.WriteLine("HelpLink = " + myException.HelpLink);
     Console.WriteLine("Message = " + myException.Message);
     Console.WriteLine("Source = " + myException.Source);
     Console.WriteLine("StackTrace = " + myException.StackTrace);
     Console.WriteLine("TargetSite = " + myException.TargetSite);
   }
 }

}

      </source>

refines the System.Exception base class with name of the type and time of exception to create your own Exception

<source lang="csharp"> using System; public class ConstructorException : Exception {

   public ConstructorException(object origin)
       : this(origin, null) {
   }
   public ConstructorException(object origin, Exception innerException)
       : base("Exception in constructor", innerException) {
       prop_Typename = origin.GetType().Name;
       prop_Time = DateTime.Now.ToLongDateString() + " " +
           DateTime.Now.ToShortTimeString();
   }
   protected string prop_Typename = null;
   public string Typename {
       get {
           return prop_Typename;
       }
   }
   protected string prop_Time = null;
   public string Time {
       get {
           return prop_Time;
       }
   }

} public class Starter {

   public static void Main() {
       try {
           MyClass obj = new MyClass();
       } catch (ConstructorException except) {
           Console.WriteLine(except.Message);
           Console.WriteLine("Typename: " + except.Typename);
           Console.WriteLine("Occured: " + except.Time);
       }
   }

} class MyClass {

   public MyClass() {
       // initialization fails
       throw new ConstructorException(this);
   }

}

</source>

Use a custom Exception for RangeArray errors

<source lang="csharp"> /* C#: The Complete Reference by Herbert Schildt Publisher: Osborne/McGraw-Hill (March 8, 2002) ISBN: 0072134852

• /

// Use a custom Exception for RangeArray errors.

using System;

// Create an RangeArray exception. class RangeArrayException : ApplicationException {

 // Implement the standard constructors 
 public RangeArrayException() : base() { } 
 public RangeArrayException(string str) : base(str) { }  

 // Override ToString for RangeArrayException. 
 public override string ToString() { 
   return Message; 
 } 

}

// An improved version of RangeArray. class RangeArray {

 // private data 
 int[] a; // reference to underlying array   
 int lowerBound; // lowest index 
 int upperBound; // greatest index 

 int len; // underlying var for Length property 
   
 // Construct array given its size.  
 public RangeArray(int low, int high) {  
   high++; 
   if(high <= low) { 
     throw new RangeArrayException("Low index not less than high."); 
   } 
   a = new int[high - low];  
   len = high - low;   

   lowerBound = low; 
   upperBound = --high; 
 }  
 
 // Read-only Length property.  
 public int Length {  
   get {  
     return len;  
   }  
 }  

 // This is the indexer for RangeArray.  
 public int this[int index] {  
   // This is the get accessor.  
   get {  
     if(ok(index)) {  
       return a[index - lowerBound];  
     } else {  
       throw new RangeArrayException("Range Error."); 
     } 
   }  
 
   // This is the set accessor. 
   set {  
     if(ok(index)) {  
       a[index - lowerBound] = value;  
     }  
     else throw new RangeArrayException("Range Error."); 
   }  
 }  
 
 // Return true if index is within bounds.  
 private bool ok(int index) {  
   if(index >= lowerBound & index <= upperBound) return true;  
   return false;  
 }  

}

// Demonstrate the index-range array. public class RangeArrayDemo1 {

 public static void Main() {   
   try { 
     RangeArray ra = new RangeArray(-5, 5);  
     RangeArray ra2 = new RangeArray(1, 10);  

     // Demonstrate ra 
     Console.WriteLine("Length of ra: " + ra.Length); 

     for(int i = -5; i <= 5; i++) 
       ra[i] = i; 
  
     Console.Write("Contents of ra: "); 
     for(int i = -5; i <= 5; i++) 
       Console.Write(ra[i] + " "); 

     Console.WriteLine("\n"); 

     // Demonstrate ra2 
     Console.WriteLine("Length of ra2: " + ra2.Length); 

     for(int i = 1; i <= 10; i++) 
       ra2[i] = i; 

     Console.Write("Contents of ra2: "); 
     for(int i = 1; i <= 10; i++) 
       Console.Write(ra2[i] + " "); 

     Console.WriteLine("\n"); 

   } catch (RangeArrayException exc) { 
      Console.WriteLine(exc); 
   } 

   // Now, demonstrate some errors. 
   Console.WriteLine("Now generate some range errors."); 

   // Use an invalid constructor. 
   try { 
     RangeArray ra3 = new RangeArray(100, -10); // Error 
  
   } catch (RangeArrayException exc) { 
      Console.WriteLine(exc); 
   } 

   // Use an invalid index. 
   try { 
     RangeArray ra3 = new RangeArray(-2, 2);  

     for(int i = -2; i <= 2; i++) 
       ra3[i] = i; 

     Console.Write("Contents of ra3: "); 
     for(int i = -2; i <= 10; i++) // generate range error 
       Console.Write(ra3[i] + " "); 

   } catch (RangeArrayException exc) { 
      Console.WriteLine(exc); 
   } 
 }  

}

      </source>

uses some of the properties of the Exception class

<source lang="csharp"> using System; using System.Reflection; public class Starter {

   public static bool bException = true;
   public static void Main() {
       try {
           MethodA();
       } catch (Exception except) {
           Console.WriteLine(except.Message);
           bException = false;
           except.TargetSite.Invoke(null, null);
       }
   }
   public static void MethodA() {
       if (bException) {
           throw new ApplicationException("exception message");
       }
   }

}

</source>

Use the NullReferenceException

<source lang="csharp"> /* C#: The Complete Reference by Herbert Schildt Publisher: Osborne/McGraw-Hill (March 8, 2002) ISBN: 0072134852

• /

// Use the NullReferenceException.

using System;

class X {

 int x; 
 public X(int a) { 
   x = a; 
 } 

 public int add(X o) { 
   return x + o.x; 
 } 

}

// Demonstrate NullReferenceException. public class NREDemo {

 public static void Main() {   
   X p = new X(10); 
   X q = null; // q is explicitly assigned null 
   int val; 

   try { 
     val = p.add(q); // this will lead to an exception 
   } catch (NullReferenceException) { 
     Console.WriteLine("NullReferenceException!"); 
     Console.WriteLine("fixing...\n"); 

     // now, fix it 
     q = new X(9);   
     val = p.add(q); 
   } 

   Console.WriteLine("val is {0}", val); 
 
 }  

}

      </source>

Using checked and unchecked

<source lang="csharp"> /* C#: The Complete Reference by Herbert Schildt Publisher: Osborne/McGraw-Hill (March 8, 2002) ISBN: 0072134852

• /

// Using checked and unchecked.

using System;

public class CheckedDemo {

 public static void Main() {  
   byte a, b; 
   byte result; 

   a = 127; 
   b = 127; 
 
   try {  
     result = unchecked((byte)(a * b)); 
     Console.WriteLine("Unchecked result: " + result); 

     result = checked((byte)(a * b)); // this causes exception 
     Console.WriteLine("Checked result: " + result); // won"t execute 
   }  
   catch (OverflowException exc) {  
     // catch the exception  
     Console.WriteLine(exc); 
   }  
 }  

}

      </source>

Using checked and unchecked with statement blocks

<source lang="csharp"> /* C#: The Complete Reference by Herbert Schildt Publisher: Osborne/McGraw-Hill (March 8, 2002) ISBN: 0072134852

• /

// Using checked and unchecked with statement blocks.

using System;

public class CheckedBlocks {

 public static void Main() {  
   byte a, b; 
   byte result; 

   a = 127; 
   b = 127; 
 
   try {  
     unchecked { 
       a = 127; 
       b = 127; 
       result = unchecked((byte)(a * b)); 
       Console.WriteLine("Unchecked result: " + result); 

       a = 125; 
       b = 5; 
       result = unchecked((byte)(a * b)); 
       Console.WriteLine("Unchecked result: " + result); 
     } 

     checked { 
       a = 2; 
       b = 7; 
       result = checked((byte)(a * b)); // this is OK 
       Console.WriteLine("Checked result: " + result); 

       a = 127; 
       b = 127; 
       result = checked((byte)(a * b)); // this causes exception 
       Console.WriteLine("Checked result: " + result); // won"t execute 
     } 
   }  
   catch (OverflowException exc) {  
     // catch the exception  
     Console.WriteLine(exc); 
   }  
 }  

}

      </source>

Using Exception members

<source lang="csharp"> /* C#: The Complete Reference by Herbert Schildt Publisher: Osborne/McGraw-Hill (March 8, 2002) ISBN: 0072134852

• /

// Using Exception members.

using System;

class ExcTest {

 public static void genException() { 
   int[] nums = new int[4];  

   Console.WriteLine("Before exception is generated."); 

   // Generate an index out-of-bounds exception. 
     for(int i=0; i < 10; i++) { 
       nums[i] = i; 
       Console.WriteLine("nums[{0}]: {1}", i, nums[i]); 
     } 

   Console.WriteLine("this won"t be displayed");  
 } 

}

public class UseExcept {

 public static void Main() {  
 
   try {  
     ExcTest.genException(); 
   }  
   catch (IndexOutOfRangeException exc) {  
     // catch the exception  
     Console.WriteLine("Standard message is: "); 
     Console.WriteLine(exc); // calls ToString() 
     Console.WriteLine("Stack trace: " + exc.StackTrace); 
     Console.WriteLine("Message: " + exc.Message); 
     Console.WriteLine("TargetSite: " + exc.TargetSite); 
   }  
   Console.WriteLine("After catch statement.");  
 }  

}

      </source>