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[Page 812 (continued)]

16.2. Exception-Handling Overview

Program logic frequently tests conditions that determine how program execution proceeds. Consider the following pseudocode:


Perform a task
If the preceding task did not execute correctly
     Perform error processing
Perform next task
If the preceding task did not execute correctly
     Perform error processing
...

In this pseudocode, we begin by performing a task. We then test whether that task executed correctly. If not, we perform error processing. Otherwise, we continue with the next task. Although this form of error handling works, intermixing program logic with error-handling logic can make the program difficult to read, modify, maintain and debugespecially in large applications.

Performance Tip 16.1

If the potential problems occur infrequently, intermixing program logic and error-handling logic can degrade a program's performance, because the program must (potentially frequently) perform tests to determine whether the task executed correctly and the next task can be performed.


Exception handling enables the programmer to remove error-handling code from the "main line" of the program's execution, which improves program clarity and enhances modifiability. Programmers can decide to handle any exceptions they chooseall exceptions, all exceptions of a certain type or all exceptions of a group of related types (e.g., exception types that belong to an inheritance hierarchy). Such flexibility reduces the likelihood that errors will be overlooked and thereby makes a program more robust.

With programming languages that do not support exception handling, programmers often delay writing error-processing code or sometimes forget to include it. This results in less robust software products. C++ enables the programmer to deal with exception handling easily from the inception of a project.


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