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");
}
}
Language Basics
Derived exceptions must appear before base class exceptions
/*
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);
}
}
}
}
[/csharp]
Use a custom Exception for RangeArray errors
/*
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("
");
// 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("
");
} 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);
}
}
}
[/csharp]
Use the NullReferenceException
/*
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...
");
// now, fix it
q = new X(9);
val = p.add(q);
}
Console.WriteLine("val is {0}", val);
}
}
Using Exception members
/*
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.");
}
}
[/csharp]
illustrates the use of a System.Exception object
/*
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);
}
}
}
Demonstrates defining and using a custom exception class
/*
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;
}
}