Re: std::set<> and predicates
On 5 Okt, 15:18, Michael Doubez <michael.dou...@free.fr> wrote:
On 5 oct, 12:35, Rune Allnor <all...@tele.ntnu.no> wrote:
On 5 Okt, 09:46, James Kanze <james.ka...@gmail.com> wrote:
On Oct 5, 4:55 am, Rune Allnor <all...@tele.ntnu.no> wrote:
I am a bit confused about std::set<> and associated
predicates. I have a std::set in my application where the
predicate works as expected when tested in isolation, but
where the items inserted in the set don't match the predicate,
that is, the test
class predicate : public std::less {/*...*/};
predicate p;
std::set<size_t> s(p);
// Insert elements
std::set<size_t>::iterator i = s.begin();
std::set<size_t>::iterator j = i; j++;
bool b = p(*i,*j); // Should be true
Knowing nothing about p, it's impossible to say much. But two
things are obvious: as declared above, your set doesn't use
predicate as an ordering function, it uses std::less<size_t>;
Why is that?
According to Josuttis' table 6.20, the constructor std::set<>::set()
with the predicate as argument should use the predicate as ordering
criterion.
set<> constructor keeps a copy of the Comparator. In your case, you
have slicing at the less<size_t> base of predicate.
I could not find the related section in the standard. I will post it
if/when I find it.
No need to. I have already solved the problem with the help of
Victor's code. There were some other issues about the ctor of the
predicate, as my implementation required a copy-constructor of the
predicate which I had initially disabled. It took a little time to
sort that one out, but now everything works as desired.
Rune
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