std::vector of std::vectors contiguity

Question

I know that std::vector internally stores it\'s data contiguously (unless it is std::vector) both in the old C++03

Answer 1

To answer your final question: No. The elements of a vector of vectors are not stored contiguously.

Consider the following code:

std::vector > vv;
.... fill in v[0], v[1], v[2], etc
std::vector  & v = vv[1];
v.push_back (23);

If they were all stored contiguously, then this would cause each element in vv[2], vv[3], etc to move. How would that possibly work, since you're just affecting a single vector 'v'?