Harvard Business School of Echec

I have discovered a nice bug in my code. I had some stuff about iterating a std::list<> and removing some elements at the same time. Like the following :

std::list<> l;

iterator it(l.begin());

while (it != l.end()) {
	if (...)
		it = l.erase(it);
	else
		++it;
}

Then i moved from std::list<> to std::set<> (ordered set). The code didn't compile as is because std::set<>::erase returns void. The STL documentation says Erasing an element from a set also does not invalidate any iterators.... OK then, no return value.

std::set<> s;

iterator it(s.begin());

while (it != s.end()) {
	if (...)
		s.erase(it);
	++it;
}

It worked nicely for a long time. But once i got a double free crash. In order to debug it, i added many print. For example {1 2 3 5 6 7} - {3} shoud have printed {1 2 5 6 7} but instead i got {1 2 2 5 6 7} or {1 5 6 7 2} !

So i read again the documentation : 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.. Bon sang !

The correct way to do it :

std::set<> s;

iterator it(s.begin())

while (it != s.end()) {
	iterator next(it);
	++next;
	if (...)
		s.erase(it);
	it = next;
}