 C＃快餐－8
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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