发信人: nice (春天), 信区: DotNET        
标  题: C＃快餐－8
发信站: BBS 水木清华站 (Thu Jul 26 02:09:18 2001)

Lesson 8.  Exceptions


    There are no exceptions in C and in C++ one can get away from using  
them with error handling functions such as exit() and terminate(). In C#  
these functions are absent and we introduce exceptions which take their place.
When a program has a bug we can intercept it in the flow of execution by  
inserting an error handling statement. For example let's say we have a program
which does not accesses the first element of an array. Then, during some array
handling operations, if an access to array[0] is attempted, the OutOfRange
exception is thrown. class OutOfRange  is an exception class. All exception  
classes inherit from class. Compiler will give an error if the inheritance  
from the Exception class is not made. In the code that follows we throw an  
exception OutOfRange if i == 0 is true. The try statement is enclosing the  
part of the code where the exception is expected. If the exception occurs it  
is handled by the code inside the catch statement. The catch statement  takes  
as an argument an instance of class System.Exception.

//first exception handling program
using System;
class OutOfRange: Exception{
}
class Demo
{
    int n;
    public int []array;
    public Demo ( int n)
    {
        this.array = new int[n];
        this.n = n;
    }
    public void show_element (int i)
    {
        try
        {
            if (i == 0) throw ( new OutOfRange());
        }
        catch (Exception e)
        {
            Console.WriteLine("Exception : {0}", e);
        }
        Console.WriteLine (array [i]);
    }
}
class Test
{
    public static void Main()
    {
        Demo test = new  Demo (3);
        test.array [1] = 2;
        test.array [2] = 3;
        test.show_element (0);
    }
}

The output is :
Exception : OutOfRange: An exception of type OutOfRange was thrown. at Demo.
show_element(Int32 i) in G:\CSharpEd\excep.cs:line 19
0

The previous program can be simplified if you use a built in Exception class
provided by the C# runtime. The full list of built in Exception classes  
hasn't been published yet by Microsoft at the time of this writing.
OutOfMemoryException  Thrown when an allocation of  memory  fails.
StackOverflowException  Infinite recursion.
IndexOutOfRangeException  Out of bounds access to an array
ArithmeticException  A base class for exceptions DivideByZeroException and O
verflowException
OverflowException  Overlflow
DivideByZeroException  Division by zero
In the following program I use built in ArgumentException instead of  
OutOfRange exception.

//a better way to handle an Argument exception
using System;
class Demo
{
    int n;
    public int []array;
    public Demo (int n)
    {
        this .array = new int [n];
        this .n = n;
    }
    public void show_element (int i)
    {
        try
        {
            if (i == 0) throw new ArgumentException ("Out of rannge");
        }
        catch (ArgumentException e)
        {
            Console.WriteLine("Exception : {0}", e);
            return ;
        }
        Console.WriteLine (array [i]);
    }
}
class Test
{
    public static void Main()
    {
        Demo test = new Demo(3);
        test.array [1] = 2;
        test.array [2] = 3;
        test.show_element (0);
    }
}

Write a simple program which divides two integers and try using DivideByZero
Exception exception. Good Luck!

--

※ 修改:·walts 於 Jul 26 10:10:41 修改本文·[FROM: 166.111.142.118]
※ 来源:·BBS 水木清华站 smth.org·[FROM: 166.111.176.234]
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