Exceptions and pre-conditions

Exceptions

An exception is an anomalous or exceptional condition requiring special processing – often changing the normal flow of program execution.

Be careful not to confuse an exception with an error.

An error "indicates serious problems that a reasonable application should not try to catch." An Exception "indicates conditions that a reasonable application might want to catch.".

We use the term "catch an exception" to catch exceptions and plan how the program should respond.

Identifying exceptions

The exceptions below are common. There are many other types of exceptions.

1. consider different data types (are you passing an int to a function which is expecting a string?)
2. consider inaccurate user input (accidental or deliberate)
3. consider writing or reading a to file - there could be a failure opening, writing, or closing to file
4. consider memory limitations - this is especially important when you are working with large datasets
5. consider the possibility a user might attempt to interrupt the program (usually by pressing control-C).

For a list of common exceptions, please click here

Example

Standards

These standards are used from the IB Computer Science Subject Guide

• Identify exceptions that need to be considered in a specified problem solution.

anomalous or exceptional conditions requiring special processing – often changing the normal flow of program execution

anomalous or exceptional conditions requiring special processing – often changing the normal flow of program execution

anomalous or exceptional conditions requiring special processing – often changing the normal flow of program execution

anomalous or exceptional conditions requiring special processing – often changing the normal flow of program execution

Give a sequence of brief answers with no explanation.

Provide an answer from a number of possibilities. Recognize and state briefly a distinguishing fact or feature.