Exception handling is a special processing that may required after detection of an exception. Exception handling code unit is called an exception handler. There are many program that allow program to trap input/output errors(including EOF). An exception is any usual event, either erroneous or not, detectable by either hardware or software, that may require special processing.

In a language without exception handling, when an exception occurs, control goes to the operating system, where a message is displayed and the program is terminated.

In a language with exception handling, program are allowed to trap some exceptions, thereby providing the possibility of fixing the problem and continuing.

Advantages of built-in exception handling :

  • Error detection code is tedious to write and it clutters the program
  • Exception handling encourages programmers to consider many different possible errors
  • Exception propagation allows a high level of reuse of exception handling code

Exception handling control flow

C++ exception handlers,

  • Exception Handlers Form:

               try {

— code that is expected to raise an exception


catch (formal parameter) {

handler code


catch (formal parameter) {

handler code



Catch function,

  • catch is the name of all handlers–it is an overloaded name, so the formal parameter of each must be unique
  • The formal parameter need not have a variable,

It can be simply a type name to distinguish the handler it is in from others

  • The formal parameter can be used to transfer information to the handler
  • The formal parameter can be an ellipsis, in which case it handles all exceptions not yet handled


Throwing exceptions,

  • Exceptions are all raised explicitly by the statement:

               throw [expression];

  • The brackets are metasymbols
  • A throw without an operand can only appear in a handler; when it appears, it simply re-raises the exception, which is then handled elsewhere
  • The type of the expression disambiguates the intended handler


Unhandled exception,

  • An unhandled exception is propagated to the caller of the function in which it is raised
  • This propagation continues to the main function
  • If no handler is found, the default handler is called


Event handling, an event is a notification that something specific has occurred, such as a mouse click on a graphical button. Event handler is a segment of code that is executed in response to an event.

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