If the error condition is something that caller of your library could have prevented by changing logic of their code then derive your exception from logic_error. Generally, caller won't be able to do simple retry if logic_error is thrown. For example, someone is calling your code such that it would cause divide by 0 then you may create custom exception,
class divide_by_zero : public logic_error {
public:
divide_by_zero(const string& message)
: logic_error(message) {
}
}
If the error condition was something that could not have been prevented by the caller then derive from runtime_error. Some of these errors might be recoverable (i.e. caller can catch exception, re-try or ignore).
class network_down : public runtime_error {
public:
network_down(const string& message)
: runtime_error(message) {
}
}
This is also the general philosophy to design exceptions in standard library. You can view the exception code for GCC here.
