C++ exceptions

As the name suggests, exceptions are for exceptional conditions. They are not normal conditions. They are not conditions that you want to occur but they are conditions that may happen. Any exceptional condition will often mean that your data will be in an inconsistent state, so using exceptions means that you need to think in transactional terms, that is, an operation either succeeds, or the state of an object should remain the same as it was before the operation was attempted. When an exception occurs in a code block, everything that happened in the code block will be invalid. If the code block is part of a wider code block (say, a function that is a series of function calls by another function) then the work in that other code block will be invalid. This means that the exception may propagate out to other code blocks further up the call stack, invalidating the objects that depend on the operation being successful. At some point, the exceptional condition will be recoverable...