Exception handling

Abstract

Thus far we have concentrated on writing programs as correctly as possible. However, each program is embedded in a larger context and must communicate with its environment. We make a number of assumptions about the environment (indeed, we incorporate these assumptions into our programs) that must apply in order for our program to work at all: input data must be present, there must be space on the hard disk for writing results, numeric values must be in certain valid ranges, etc. However, certainly some exception situations arise where these assumptions do not apply. The program must handle these situations also, without crashing or producing erroneous results. In addition, we could design the program so that it tests all possible errors in every Situation. However, this strategy would prove quite involved and unnatural.