Ivor Horton's Beginning Visual C++ 2012

EXCEPTIONS

If you’ve had a go at the exercises that appear at the end of the previous chapters, you’ve more than likely come across compiler errors and warnings, as well as errors that occur while the program is running. Exceptions are a way of flagging errors or unexpected conditions that occur in your programs, and you already know that the new operator throws an exception if the memory you request cannot be allocated.

So far, you have typically handled error conditions by using an if statement to test some expression, and then executing some specific code to deal with the error. C++ provides another, more general mechanism for handling errors that allows you to separate the code that deals with these conditions from the code that executes when such conditions do not arise. It is important to realize that exceptions are not intended to be used as an alternative to the normal data checking and validating that you might do in a program. The code that is generated when you use exceptions carries quite a bit of overhead with it, so exceptions are really intended to be applied in the context of exceptional, near-catastrophic conditions that might arise, but are not normally expected to occur in the normal course of events. An error reading from a disk might be something that you use exceptions for. An invalid data item being entered is not a good candidate for using exceptions.

The exception mechanism uses three new keywords:

• try–Identifies a code block in which an exception can ...