Chapter 20 C Namespace and Exceptions

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Chapter 20 C Namespace and Exceptions

• By C. Shing
• ITEC Dept
• Radford University

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Objectives

• Understand how to create namespace
• Understand how to throw exception
• Understand how to handle exception

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Namespace

• Contains unique names which are defined
• in the space
• The names are unique in their scope
• Can be defined more than once,
• such as define the specification once and
• define the implementation the second time

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Namespace (Cont.)

• Form
• define
• namespace yournamespace
• class specification/implementation
• Invoke the names
• using namespace yournamespace

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Example

• Namespaces for using data structures
• linked list, stack, queue and tree
• name.h

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Example (Cont.)

• Use namespaces for data structures
• linked list, stack, queue and tree
• uselist.cpp
• usestack.cpp
• usequeue.cpp
• usetree.cpp

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Exception

• An unusual situation that makes the code
• not working as normal
• Handle unusual situation so they will be
• executed normally
• If exception not handled, then system will
• execute terminate to end the execution of
• the program

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Exception (Cont.)

• Form
• try
• exeception could occur here
• catch (exception type1)
• exeception handled here
• catch (exception type2)
• exeception handled here

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Exception (Cont.)

• If exception happens in try block, the code ended
  
• at throw line. Then control moved to catch block
• and finished in the block.
• If no exception happen in try block, then control
  
• will move to the statement after the catch
  block.
• When catch exception, it will start from the
• 1st catch block down one by one until it finds
  the
• corresponding exception type

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Handle Exception

1. Use library routines
2. Use user defined exeception

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Handle Exception library exception

• Example
• bubbleclass_template.cpp
• bubbleclasstemplate_data.txt

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Handle Exception user-defined exception

• Write function that throw exception
• Can have any possible exception type
• returntype functionname ()
• if () throw exception1
• Only exception1, exception2, listed are
  possible
• returntype functionname ()
• throw exception1, exception2,
• if () throw exception1

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Handle Exception user-defined exception (Cont.)

• Write function that throw exception (Cont.)
• If not in case 1 or 2, then the system will
• terminate abnormally

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Handle Exception user-defined exception (Cont.)

• The exception can be a class and arranged
• in inheritance hierarchy
• superclass must throw all the exceptions that
• all subclasses have thrown
• If the exception is not caught in the subclass
  that
• was thrown, it must be caught from the bottom of
  
• the hierarchy up.

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References

• Deitel Deitel C How to Program, 4th ed.,
• Chapter 23, Prentice Hall