C# Cookbook

5.4. Handling Derived Exceptions Individually

Problem

You have an exception hierarchy that consists of a base exception class and multiple derived exception classes. At some point in your code, you want to handle only one or two of these derived exceptions in a specific manner. All other derived exceptions should be handled in a more generic manner. You need a clean way to target specific exceptions in an exception class hierarchy to be handled differently from the rest.

Solution

The exception handlers for C# allow for multiple catch clauses to be implemented. Each of these catch clauses can take a single parameter—a type derived from the Exception class. An exception handler that uses multiple catch clauses is shown here:

try
{
    int d = 0;
    int z = 1/d;
}
catch(DivideByZeroException dbze)
{
    Console.WriteLine("A divide by zero exception occurred. Error message == "
      + dbze.Message);
}
catch(OverflowException ofe)
{
    Console.WriteLine("An Overflow occurred. Error message == " + ofe.Message);
}
catch(Exception e)
{
    Console.WriteLine("Another type of error occurred. Error message == " 
      + e.Message);
}

This code produces the following output:

A divide by zero exception occurred. Error message == Attempted to divide by zero.

Discussion

Notice the exception types that each catch clause handles in this try-catch block. These specific exception types will be handled on an individual basis within their own catch block. Suppose the try block looked as follows:

try { int z2 = 9999999; checked{z2 *= 999999999;} ...