Transferring elements between vectors

What this C++ vector-semantics interview question tests

This is a hard question that probes deep familiarity with C++ move semantics, iterator validity, and the lifetime of temporary objects. It is the kind of question quant firms ask to distinguish candidates who have only surface-level C++ knowledge from those who understand the language's memory model and object lifecycle in detail.

To answer correctly, you need to reason carefully about what happens when elements are transferred between containers—specifically, how move operations interact with iterator invalidation, temporary object destruction, and the state of source and destination vectors. The question rewards precise knowledge of the standard library's guarantees and potential pitfalls in real-world code.

• Move semantics and rvalue references
• Iterator invalidation rules for std::vector
• Lifetime and destruction of temporary objects
• The difference between move assignment and move construction