Is the following code guaranteed to work? I have a hashed set of pointers,
which I would like to selectively delete from. Can I iterate through the
set, deleting certain ones, without invalidating the iterator? This
ominous statement in the STL "set" documentation makes me worried. I saw
no similar statement on the "hash_multi set" docs.
"Erasing an element from a set also does not invalidate any iterators,
except, of course, for iterators that actually point to the element that is
being erased."
hash_multiset<m ytype*> myset;
// insert a bunch of mytype pointers into myset
for (hash_multiset< mytype*>::itera tor i=myset.begin() ; i!=myset.end(); i++)
if (mytype->someproperty () == 1) {
mytype* p = *i;
myset.erase(i);
delete p;
}
Thanks.
3  3083 
"Kenneth Massey" <ke******@vt.ed u> wrote in message
news:2gwLc.4988 $_K2.2563@laker ead02... Is the following code guaranteed to work? I have a hashed set of
pointers, which I would like to selectively delete from. Can I iterate through the
set, deleting certain ones, without invalidating the iterator? This
ominous statement in the STL "set" documentation makes me worried. I saw
no similar statement on the "hash_multi set" docs.
"Erasing an element from a set also does not invalidate any iterators,
except, of course, for iterators that actually point to the element that
is being erased."
hash_multiset<m ytype*> myset;
// insert a bunch of mytype pointers into myset
for (hash_multiset< mytype*>::itera tor i=myset.begin() ; i!=myset.end();
i++) if (mytype->someproperty () == 1) {
mytype* p = *i;
myset.erase(i);
delete p;
}
Well you ARE invalidating the iterator, because it does point to the element
being erased. You erase i and then you do i++, that is using an invalidated
iterator.
Here's how to do it
hash_multiset<m ytype*>::iterat or i=myset.begin() ;
while (i!=myset.end() )
{
if (mytype->someproperty () == 1)
{
mytype* p = *i;
myset.erase(i++ );
delete p;
}
else
{
++i;
}
}
By saying 'myset.erase(i+ +);' you make sure that the iterator is incremented
before you erase not afterwards.
john
> mytype* p = *i; myset.erase(i++ );
delete p;
Incidentally there is no need for the variable p.
delete *i;
myset.erase(i++ );
john
John Harrison wrote: mytype* p = *i;
myset.erase(i++ );
delete p;
Incidentally there is no need for the variable p.
delete *i;
myset.erase(i++ );
john
Thanks for the help.
Actually I want to make sure the pointer is deleted *after* the set entry
has been erased. My hash and equal functions reference the pointer through
->, and I don't want to risk them being called on a deleted pointer. This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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