Exception safety

Never allow an exception to escape from a destructor or from an overloaded operator delete() or operator delete[](); write every destructor and deallocation as though it had an exception specification of “throw()”

In each function, take all the code that might emit an exception and do all the work safely off to the side. Only then, when you know that the real work has succeeded, should you modifiy the program state (and clean up) using only non-throwing operations.