You did not provide the whole code, so I cannot tell what's wrong. I'll guess though: You're making a copy of the "dag" object. When you make a copy, the iterator continues to point to the original vector's element, not the copy. If the original vector is deallocated after copying, you will have an iterator pointing nowhere.
E.g.
dag GetDag()
{
dag gruu;
return gruu;
}
void meow()
{
dag tmp = GetDag(); // this does copying, original gets destructed
tmp.triangulate(); // works on an obsolete iterator
}
To fix, follow either one of these solutions:
1) Instead of a storing an iterator possessing a pointer, store an index
2) Implement the copy constructor and the assign operator.
