C++ :: Deleting Iterator Inside A Double Loop

I know that if I erase a value inside an iterator, it becomes invalidated, and this is how you would normally fix it:

for(std::vector<int>::iterator it = list.begin(); it<list.end(); ) {
if((*it) == 5)
list.erase(it);
else
it++;
}

But what about a double loop? like this one:

This would delete all duplicates

for(std::vector<int>::iterator it = list.begin(); it<list.end(); it++) {
for(std::vector<int>::iterator it2 = list.begin(); it2<list.end(); it2++) {
if((*it) == (*it2))
list.erase(it2);
}
}