From:

"Greg Herlihy" <greghe@pacbell.net>

Newsgroups:

comp.lang.c++.moderated

Date:

8 Jun 2006 18:54:35 -0400

Message-ID:

<1149749505.895273.78480@h76g2000cwa.googlegroups.com>

Neither of the two methods, lower_bound and upper_bound, for std::set

does return the iterator less than the key specified. Is there a

better way to approach this?

template <typename Set>

typename Set::const_reverse_iterator less_lower_bound(Set const & set,

typename Set::const_reference key) {

Set::key_compare key_comp = set.key_comp();

Set::const_reverse_iterator i = set.rbegin();

for (; i != set.rend(); ++i) {

if (!key_comp(key, *i)) {

break;

}

}

return i;

}

does return the iterator less than the key specified. Is there a

better way to approach this?

template <typename Set>

typename Set::const_reverse_iterator less_lower_bound(Set const & set,

typename Set::const_reference key) {

Set::key_compare key_comp = set.key_comp();

Set::const_reverse_iterator i = set.rbegin();

for (; i != set.rend(); ++i) {

if (!key_comp(key, *i)) {

break;

}

}

return i;

}

There is certainly a less complicated solution: obtain the lower bound

iterator for the key from the set, then compare it against the set's

begin() iterator. If they compare unequal then decrement the

lower_bound iterator to find the iterator in question. If instead the

two iterators compare equal, then it is certain that no value lower

than the specified key is present in the set.

Greg

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