Handling Exceptions (WHEN … DO)

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Instead of terminating when an exception occurs, a procedure can respond to and perhaps correct the error condition by handling the exception. When an exception is raised, it:

  • Terminates execution of the BEGIN END block containing the exception and undoes any actions performed in the block.
  • Backs out one level to the next BEGIN END block and seeks an exception-handling (WHEN) statement, and continues backing out levels until one is found. If no WHEN statement is found, the procedure is terminated and all its actions are undone.
  • Performs the ensuing statement or block of statements specified after WHEN, if found.
  • Returns program control to the block or statement in the procedure following the WHEN statement.
Note: An exception that is handled with WHEN does not return an error message.

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