Csharp/C Sharp/Language Basics/Exception Try Catch

An exception can be generated by one method and caught by another

/*
C#: The Complete Reference 
by Herbert Schildt 
Publisher: Osborne/McGraw-Hill (March 8, 2002)
ISBN: 0072134852
*/
/* An exception can be generated by one 
   method and caught by another. */ 
 
using System; 
 
class ExcTest { 
  // Generate an exception. 
  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 ExcDemo2 {  
  public static void Main() {  
  
    try {  
      ExcTest.genException(); 
    }  
    catch (IndexOutOfRangeException) {  
      // catch the exception  
      Console.WriteLine("Index out-of-bounds!");  
    }  
    Console.WriteLine("After catch statement.");  
  }  
}

Catch different exceptions

/*
C# Programming Tips & Techniques
by Charles Wright, Kris Jamsa
Publisher: Osborne/McGraw-Hill (December 28, 2001)
ISBN: 0072193794
*/
namespace nsCompare
{
    using System;
    public class Compare
    {
        static public void Main (string [] args)
        {
            int TestArg;
            try
            {
                TestArg = int.Parse (args[0]);
            }
            catch (FormatException)
            {
                Console.WriteLine ("Please enter a number value.");
                return;
            }
            catch (IndexOutOfRangeException)
            {
                Console.WriteLine ("Please enter an argument");
                return;
            }
            string str;
            str = TestArg > 10 ? "The test is true" : "The test is false";
            Console.WriteLine (str);
        }
    }
}

Catch Divide By Zero Exception

/*
C# Programming Tips & Techniques
by Charles Wright, Kris Jamsa
Publisher: Osborne/McGraw-Hill (December 28, 2001)
ISBN: 0072193794
*/
namespace nsDivZero
{
    using System;
    public class DivZero
    {
        static public void Main ()
        {
            // Set an integer equal to 0
            int IntVal1 = 0;
            // and another not equal to zero
            int IntVal2 = 57;
            try
            {
                Console.WriteLine ("{0} / {1} = {2}", IntVal2, IntVal1, IntResult (IntVal2, IntVal1) / IntResult (IntVal2, IntVal1));
            }
            catch (DivideByZeroException e)
            {
                Console.WriteLine (e.Message);
            }
            // Set a double equal to 0
            double dVal1 = 0.0;
            double dVal2 = 57.3;
            try
            {
                Console.WriteLine ("{0} / {1} = {2}", dVal2, dVal1, DoubleResult (dVal2, dVal1));
            }
            catch (DivideByZeroException e)
            {
                Console.WriteLine (e.Message);
            }
        }
        static public int IntResult (int num, int denom)
        {
            return (num / denom);
        }
        static public double DoubleResult (double num, double denom)
        {
            return (num / denom);
        }
    }
}

Catch Error

using System;
public class CatchError
{
    public static void Main()
    {
        int var1 = 1000, var2 = 0, var3;
        try
        {
            var3 = var1 / var2;
        }
        catch (ArithmeticException e)
        {
            Console.WriteLine("Exception: {0}", e.ToString());
            var3 = -1;
        }
        catch (Exception e)
        {
            Console.WriteLine("Exception: {0}", e.ToString());
            var3 = -2;
        }
        Console.WriteLine("The result is: {0}", var3);
    }
}

Catches an exception that was thrown in a component

/*
C# Programming Tips & Techniques
by Charles Wright, Kris Jamsa
Publisher: Osborne/McGraw-Hill (December 28, 2001)
ISBN: 0072193794
*/
// FileOpen.cs -- Catches an exception that was thrown in a component
//
//                Compile this program with the following command line:
//                    C:>csc /r:fopen.dll FileOpen.cs
//
namespace nsFileOpen
{
    using System;
    using System.IO;
    class clsMain
    {
        static public void Main ()
        {
            clsFile file;
            try
            {
                file = new clsFile ("");
            }
            catch (Exception e)
            {
                Console.WriteLine (e.Message);
                Console.WriteLine ("Exception handled in client");
            }
        }
    }
}

// Fopen.cs -- program to show exception handling in a component
//
//             Compile this program with the following command line:
//                 C:>csc /t:library Fopen.cs
//
namespace nsFileOpen
{
    using System;
    using System.IO;
    public class clsFile
    {
        FileStream strm;
        public clsFile (string FileName)
        {
            strm = new FileStream (FileName, FileMode.Open,
                                             FileAccess.Read);
        }
    }
}

Demonstrate exception handling

/*
C#: The Complete Reference 
by Herbert Schildt 
Publisher: Osborne/McGraw-Hill (March 8, 2002)
ISBN: 0072134852
*/
// Demonstrate exception handling. 
 
using System; 
 
public class ExcDemo1 { 
  public static void Main() { 
    int[] nums = new int[4]; 
 
    try { 
      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"); 
    } 
    catch (IndexOutOfRangeException) { 
      // catch the exception 
      Console.WriteLine("Index out-of-bounds!"); 
    } 
    Console.WriteLine("After catch statement."); 
  } 
}

Demonstrates stacking catch blocks to provide alternate code for more than one exception type

/*
C# Programming Tips & Techniques
by Charles Wright, Kris Jamsa
Publisher: Osborne/McGraw-Hill (December 28, 2001)
ISBN: 0072193794
*/
// Except.cs -- Demonstrates stacking catch blocks to provide alternate code for
// more than one exception type.
//
// Compile this program with the following command line:
//    C:>csc Except.cs
//
namespace nsExcept
{
    using System;
    using System.IO;
    
    public class Except
    {
        static public void Main (string [] args)
        {
            if (args.Length == 0)
            {
                Console.WriteLine ("Please enter a file name");
                return;
            }
            try
            {
                ReadFile (args[0]);
            }
            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)
        {
            FileStream strm = new FileStream (FileName, FileMode.Open,
                                                        FileAccess.Read);
            StreamReader reader = new StreamReader (strm);
            string str = reader.ReadToEnd ();
            Console.WriteLine (str);
        }
    }
}

Demonstrates using if statements to sort out an IOException

/*
C# Programming Tips & Techniques
by Charles Wright, Kris Jamsa
Publisher: Osborne/McGraw-Hill (December 28, 2001)
ISBN: 0072193794
*/
// IOExcept.cs -- Demonstrates using if statements to sort out an IOException
//
//                Compile this program with the following command line:
//                    C:>csc IOExcept.cs
//
namespace nsExcept
{
    using System;
    using System.IO;
    public class IOExcept
    {
        static public void Main (string [] args)
        {
            if (args.Length == 0)
            {
                Console.WriteLine ("Please enter a file name");
                return;
            }
            ReadFile (args[0]);
        }
        static public void ReadFile (string FileName)
        {
            FileStream strm = null;
            StreamReader reader = null;
            try
            {
                strm = new FileStream (FileName, FileMode.Open,
                                                   FileAccess.Read);
                reader = new StreamReader (strm);
                while (reader.Peek() > 0)
                {
                    string str = reader.ReadLine();
                    Console.WriteLine (str);
                }
            }
            catch (IOException e)
            {
                if (e is EndOfStreamException)
                {
                    Console.WriteLine ("Attempted to read beyond end of file");
                }
                else if (e is FileNotFoundException)
                {
                    Console.WriteLine ("The file name " + FileName +
                                       " cannot be found");
                    return;
                }
                else if (e is DirectoryNotFoundException)
                {
                    Console.WriteLine ("The path for name " + FileName +
                                       " cannot be found");
                    return;
                }
                else if (e is FileLoadException)
                {
                    Console.WriteLine ("Cannot read from " + FileName);
                }
                reader.Close();
                strm.Close ();
            }
            catch (Exception e)
            {
                Console.WriteLine (e.Message);
            }
        }
    }
}

Exception Handling:Trying and Catching

using System;
public class TryingCatching
{
    static int Zero = 0;
    public static void Main()
    {
        // watch for exceptions here
        try
        {
            int j = 22 / Zero;
        }
        // exceptions that occur in try are transferred here
        catch (Exception e)
        {
            Console.WriteLine("Exception " + e.Message);
        }
        Console.WriteLine("After catch");
    }
}

Exception Type Mismatch

/*
C#: The Complete Reference 
by Herbert Schildt 
Publisher: Osborne/McGraw-Hill (March 8, 2002)
ISBN: 0072134852
*/
// This won"t work! 
 
using System; 
 
public class ExcTypeMismatch {  
  public static void Main() {  
    int[] nums = new int[4];  
  
    try {  
      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");  
    }  
 
    /* Can"t catch an array boundary error with a 
       DivideByZeroException. */ 
    catch (DivideByZeroException) {  
      // catch the exception  
      Console.WriteLine("Index out-of-bounds!");  
    }  
    Console.WriteLine("After catch statement.");  
  }  
}

Handle error gracefully and continue

/*
C#: The Complete Reference 
by Herbert Schildt 
Publisher: Osborne/McGraw-Hill (March 8, 2002)
ISBN: 0072134852
*/
// Handle error gracefully and continue. 
 
using System; 
 
public class ExcDemo3 { 
  public static void Main() { 
    int[] numer = { 4, 8, 16, 32, 64, 128 }; 
    int[] denom = { 2, 0, 4, 4, 0, 8 }; 
 
    for(int i=0; i < numer.Length; i++) { 
      try { 
        Console.WriteLine(numer[i] + " / " + 
                          denom[i] + " is " + 
                          numer[i]/denom[i]); 
      } 
      catch (DivideByZeroException) { 
        // catch the exception 
        Console.WriteLine("Can"t divide by Zero!"); 
      } 
    } 
  } 
}

illustrates a nested try/catch block

/*
Mastering Visual C# .NET
by Jason Price, Mike Gunderloy
Publisher: Sybex;
ISBN: 0782129110
*/
/*
  Example13_5.cs illustrates a nested try/catch block;
  the nested if throws an exception that is propagated to the
  outer exception
*/
using System;
public class Example13_5
{
  public static void Main()
  {
    try
    {
      // a nested try and catch block
      try
      {
        int[] myArray = new int[2];
        Console.WriteLine("Attempting to access an invalid array element");
        myArray[2] = 1;  // throws the exception
      }
      catch (DivideByZeroException e)
      {
        // code that handles a DivideByZeroException
        Console.WriteLine("Handling a DivideByZeroException");
        Console.WriteLine("Message = " + e.Message);
        Console.WriteLine("StackTrace = " + e.StackTrace);
      }
    }
    catch (IndexOutOfRangeException e)
    {
      // code that handles an IndexOutOfRangeException
      Console.WriteLine("Handling an IndexOutOfRangeException");
      Console.WriteLine("Message = " + e.Message);
      Console.WriteLine("StackTrace = " + e.StackTrace);
    }
  }
}

illustrates an unhandled exception

/*
Mastering Visual C# .NET
by Jason Price, Mike Gunderloy
Publisher: Sybex;
ISBN: 0782129110
*/
/*
  Example13_7.cs illustrates an unhandled exception
*/
using System;
public class Example13_7
{
  public static void Main()
  {
    int[] myArray = new int[2];
    Console.WriteLine("Attempting to access an invalid array element");
    myArray[2] = 1;
  }
}

illustrates exception propagation with methods

/*
Mastering Visual C# .NET
by Jason Price, Mike Gunderloy
Publisher: Sybex;
ISBN: 0782129110
*/
/*
  Example13_6.cs illustrates exception propagation
  with methods
*/
using System;

// declare the ExceptionsTest class
class ExceptionsTest
{
  public void AccessInvalidArrayElement()
  {
    int[] myArray = new int[2];
    try
    {
      Console.WriteLine("Attempting to access an invalid array element");
      myArray[2] = 1;
    }
    catch (IndexOutOfRangeException e)
    {
      Console.WriteLine("Handling an IndexOutOfRangeException");
      Console.WriteLine("Message = " + e.Message);
      Console.WriteLine("StackTrace = " + e.StackTrace);
    }
  }
  public void DivideByZero()
  {
    int zero = 0;
    Console.WriteLine("Attempting division by zero");
    int myInt = 1 / zero;
  }
}

public class Example13_6
{
  public static void Main()
  {
    ExceptionsTest myExceptionsTest = new ExceptionsTest();
    // call the AccessInvalidArrayElement() method,
    // this method handles the exception locally
    Console.WriteLine("Calling AccessInvalidArrayElement()");
    myExceptionsTest.AccessInvalidArrayElement();
    try
    {
      // call the DivideByZero() method,
      // this method doesn"t handle the exception locally and
      // so it must be handled here
      Console.WriteLine("Calling DivideByZero()");
      myExceptionsTest.DivideByZero();
    }
    catch (DivideByZeroException e)
    {
      Console.WriteLine("Handling an IndexOutOfRangeException");
      Console.WriteLine("Message = " + e.Message);
      Console.WriteLine("StackTrace = " + e.StackTrace);
    }
  }
}

illustrates how to handle a specific exception

/*
Mastering Visual C# .NET
by Jason Price, Mike Gunderloy
Publisher: Sybex;
ISBN: 0782129110
*/
/*
  Example13_3.cs illustrates how to handle a specific exception
*/
using System;
public class Example13_3
{
  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 (DivideByZeroException myException)
    {
      // code that handles a DivideByZeroException
      Console.WriteLine("Message = " + myException.Message);
      Console.WriteLine("StackTrace = " + myException.StackTrace);
    }
  }
}

illustrates multiple catch blocks

/*
Mastering Visual C# .NET
by Jason Price, Mike Gunderloy
Publisher: Sybex;
ISBN: 0782129110
*/
/*
  Example13_4.cs illustrates multiple catch blocks
*/
using System;
public class Example13_4
{
  public static void Main()
  {
    try
    {
      int[] myArray = new int[2];
      Console.WriteLine("Attempting to access an invalid array element");
      myArray[2] = 1;
    }
    catch (DivideByZeroException e)
    {
      // code that handles a DivideByZeroException
      Console.WriteLine("Handling a System.DivideByZeroException object");
      Console.WriteLine("Message = " + e.Message);
      Console.WriteLine("StackTrace = " + e.StackTrace);
    }
    catch (IndexOutOfRangeException e)
    {
      // code that handles an IndexOutOfRangeException
      Console.WriteLine("Handling a System.IndexOutOfRangeException object");
      Console.WriteLine("Message = " + e.Message);
      Console.WriteLine("StackTrace = " + e.StackTrace);
    }
    catch (Exception e)
    {
      // code that handles a generic Exception: all other exceptions
      Console.WriteLine("Handling a System.Exception object");
      Console.WriteLine("Message = " + e.Message);
      Console.WriteLine("StackTrace = " + e.StackTrace);
    }
  }
}

Passing Exceptions on to the Caller: Caller Confuse

/*
A Programmer"s Introduction to C# (Second Edition)
by Eric Gunnerson
Publisher: Apress  L.P.
ISBN: 1-893115-62-3
*/
// 04 - Exception Handling\Passing Exceptions on to the Caller\Caller Confuse
// copyright 2000 Eric Gunnerson
using System;
public class CallerConfuse
{
    public static void Main()
    {
        Summer summer = new Summer();
        try
        {
            summer.DoAverage();
        }
        catch (Exception e)
        {
            Console.WriteLine("Exception {0}", e);
        }
    }
}
public class Summer
{
    int    sum = 0;
    int    count = 0;
    float    average;
    public void DoAverage()
    {
        try
        {
            average = sum / count;
        }
        catch (DivideByZeroException e)
        {
            // do some cleanup here
            throw;
        }
    }
}

Passing Exceptions on to the Caller: Caller Inform

/*
A Programmer"s Introduction to C# (Second Edition)
by Eric Gunnerson
Publisher: Apress  L.P.
ISBN: 1-893115-62-3
*/
// 04 - Exception Handling\Passing Exceptions on to the Caller\Caller Inform
// copyright 2000 Eric Gunnerson
using System;
public class CallerInform
{
    public static void Main()
    {
        Summer summer = new Summer();
        try
        {
            summer.DoAverage();
        }
        catch (Exception e)
        {
            Console.WriteLine("Exception: {0}", e);
        }
    }
}
public class Summer
{
    int    sum = 0;
    int    count = 0;
    float    average;
    public void DoAverage()
    {
        try
        {
            average = sum / count;
        }
        catch (DivideByZeroException e)
        {
            // wrap exception in another one,
            // adding additional context.
            throw (new DivideByZeroException(
            "Count is zero in DoAverage()", e));
        }
    }
}

Several catch branches

/*
Learning C# 
by Jesse Liberty
Publisher: O"Reilly 
ISBN: 0596003765
*/
 using System;
 namespace ExceptionHandling
 {
    public class TesterExceptionHandling4
    {
       public void Run()
       {
           try
           {
               double a = 5;
               double b = 0;
               Console.WriteLine("Dividing {0} by {1}...",a,b);
               Console.WriteLine ("{0} / {1} = {2}",
                   a, b, DoDivide(a,b));
           }
               // most derived exception type first
           catch (System.DivideByZeroException)
           {
               Console.WriteLine(
                   "DivideByZeroException caught!");
           }
           catch (System.ArithmeticException)
           {
               Console.WriteLine(
                   "ArithmeticException caught!");
           }
               // generic exception type last
           catch
           {
               Console.WriteLine(
                   "Unknown exception caught");
           }
       }
        // do the division if legal
        public double DoDivide(double a, double b)
        {
            if (b == 0)
                throw new System.DivideByZeroException();
            if (a == 0)
                throw new System.ArithmeticException();
            return a/b;
        }

        static void Main()
        {
            Console.WriteLine("Enter Main...");
            TesterExceptionHandling4 t = new TesterExceptionHandling4();
            t.Run();
            Console.WriteLine("Exit Main...");
        }

    }
 }

Throw a format exception purposely to demonstrate catching a FormatException

/*
C# Programming Tips & Techniques
by Charles Wright, Kris Jamsa
Publisher: Osborne/McGraw-Hill (December 28, 2001)
ISBN: 0072193794
*/
//
// FormExce.cs -- This program will throw a format exception purposeely
//                to demonstrate catching a FormatException.
//
//                Compile this program with the following command line:
//                    C:>csc FormExcep.cs
//
namespace nsExceptions
{
    using System;
    public class FormExce
    {
        static public void Main ()
        {
            const double pi = 3.14159;
            try
            {
                Console.WriteLine ("pi = {0,0:f5", pi);
            }
            catch (FormatException e)
            {
                Console.WriteLine (e.Message);
            }
        }
    }
}

Use a nested try block

/*
C#: The Complete Reference 
by Herbert Schildt 
Publisher: Osborne/McGraw-Hill (March 8, 2002)
ISBN: 0072134852
*/
// Use a nested try block. 
 
using System; 
 
public class NestTrys { 
  public static void Main() { 
    // Here, numer is longer than denom. 
    int[] numer = { 4, 8, 16, 32, 64, 128, 256, 512 }; 
    int[] denom = { 2, 0, 4, 4, 0, 8 }; 
 
    try { // outer try 
      for(int i=0; i < numer.Length; i++) { 
        try { // nested try 
          Console.WriteLine(numer[i] + " / " + 
                             denom[i] + " is " + 
                             numer[i]/denom[i]); 
        } 
        catch (DivideByZeroException) { 
          // catch the exception 
          Console.WriteLine("Can"t divide by Zero!"); 
        } 
      } 
    }  
    catch (IndexOutOfRangeException) { 
      // catch the exception 
      Console.WriteLine("No matching element found."); 
      Console.WriteLine("Fatal error -- program terminated."); 
    } 
  } 
}

Use multiple catch statements

/*
C#: The Complete Reference 
by Herbert Schildt 
Publisher: Osborne/McGraw-Hill (March 8, 2002)
ISBN: 0072134852
*/
// Use multiple catch statements. 
 
using System; 
 
public class ExcDemo4 { 
  public static void Main() { 
    // Here, numer is longer than denom. 
    int[] numer = { 4, 8, 16, 32, 64, 128, 256, 512 }; 
    int[] denom = { 2, 0, 4, 4, 0, 8 }; 
 
    for(int i=0; i < numer.Length; i++) { 
      try { 
        Console.WriteLine(numer[i] + " / " + 
                           denom[i] + " is " + 
                           numer[i]/denom[i]); 
      } 
      catch (DivideByZeroException) { 
        // catch the exception 
        Console.WriteLine("Can"t divide by Zero!"); 
      } 
      catch (IndexOutOfRangeException) { 
        // catch the exception 
        Console.WriteLine("No matching element found."); 
      } 
    } 
  } 
}

Use the "catch all" catch statement

/*
C#: The Complete Reference 
by Herbert Schildt 
Publisher: Osborne/McGraw-Hill (March 8, 2002)
ISBN: 0072134852
*/
// Use the "catch all" catch statement. 
 
using System; 
 
public class ExcDemo5 { 
  public static void Main() { 
    // Here, numer is longer than denom. 
    int[] numer = { 4, 8, 16, 32, 64, 128, 256, 512 }; 
    int[] denom = { 2, 0, 4, 4, 0, 8 }; 
 
    for(int i=0; i < numer.Length; i++) { 
      try { 
        Console.WriteLine(numer[i] + " / " + 
                           denom[i] + " is " + 
                           numer[i]/denom[i]); 
      } 
      catch { 
        Console.WriteLine("Some exception occurred."); 
      } 
    } 
  } 
}