Hands-On Design Patterns with C++

Swap and exception safety

The most important application of swap in C++ has to do with writing exception-safe code, or, more generally, error-safe code. Here is the problem, in a nutshell—in an exception-safe program, throwing an exception should never leave the program in an undefined state. More generally, an error condition should never leave the program in an undefined state. Note that the error does not need to be handled by means of an exception—for example, returning an error code from a function should also be handled without creating undefined behavior. In particular, if an operation causes an error, the resources already consumed by the operation in progress should be released. Often, an even stronger guarantee is desired—every ...