16.1. Introduction

In this chapter, we introduce exception handling. An exception is an indication of a problem that occurs during a program's execution. The name "exception" implies that the problem occurs infrequently—if the "rule" is that a statement normally executes correctly, then the "exception to the rule" is that a problem occurs. Exception handling enables programmers to create applications that can resolve (or handle) exceptions. In many cases, handling an exception allows a program to continue executing as if no problem had been encountered. A more severe problem could prevent a program from continuing normal execution, instead requiring the program to notify the user of the problem before terminating in a controlled manner. The features presented in this chapter enable programmers to write robust and fault-tolerant programs that are able to deal with problems that may arise and continue executing or terminate gracefully. The style and details of C++ exception handling are based in part on the work of Andrew Koenig and Bjarne Stroustrup, as presented in their paper, "Exception Handling for C++ (revised)."^[1]

^[1] Koenig, A., and B. Stroustrup, "Exception Handling for C++ (revised)," Proceedings of the Usenix C++ Conference, pp. 149–176, San Francisco, April 1990.

The chapter begins with an overview of exception-handling concepts, then demonstrates basic exception-handling techniques. We show these techniques via an example that demonstrates handling an exception that occurs when a function attempts to divide by zero. We then discuss additional exception-handling issues, such as how to handle exceptions that occur in a constructor or destructor and how to handle exceptions that occur if operator new fails to allocate memory for an object. We conclude the chapter by introducing several classes that the C++ Standard Library provides for handling exceptions.