C# 0 The Complete Reference

ExceptB

 is derived from 

ExceptA

, the 

catch

 for 

ExceptB

 must be before the one 

for

ExceptA

. Similarly, the 

catch

 for 

Exception

 (which is the base class for all exceptions) 

must appear last. To prove this point for yourself, try rearranging the 

catch

clauses. Doing 

so will result in a compile-time error.

One good use of a base class 

catch

 clause is to catch an entire category of exceptions. For 

example, imagine you are creating a set of exceptions for some device. If you derive all of 

the exceptions from a common base class, then applications that don’t need to know precisely 

what problem occurred could simply catch the base class exception, avoiding the unnecessary 

duplication of code.

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