Re: pure virtual functions and runtime id
On Feb 20, 5:16 pm, Juha Nieminen <nos...@thanks.invalid> wrote:
James Kanze wrote:
class Derived: public Base
{
public:
~Derived() { cleanup(); }
virtual void cleanup() { std::cout << "Derived cleanup\n"; }
};
A bit less automatic, but that's just a side-effect of OOP.
Or just have the derived classes put the cleanup code in the
destructor, where it belongs.
There may be cases where you want to clean up the object before it's
destroyed, for whatever reason. That's why it's sometimes handy to have
a separate cleanup (or whatever) function which can be called directly,
but will ultimately be called by the destructor.
It's not like this technique isn't used quite a lot. For instance, why
do you think there exists an explicit std::ifstream::close() function,
even though the stream is always closed automatically when the object is
destroyed?
Because close() can change the state of the stream, and you have
to verify after having close(). The close() in the destructor
is just a safeguard, to prevent resource leaks in case of an
exception, and shouldn't really be used in normal programming,
unless you're abandoning all processing with the file (and in
the case of an output file, deleting it as part of the error
handling).
There are times when some sort of pre-destructor would be
useful, but I don't think they're very frequent.
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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