Transferring elements between containers

Understanding C++ container transfer semantics

This is a medium-difficulty C++ language-knowledge question that tests your grasp of how standard library containers behave when elements are moved or copied between them. It rewards precise understanding of container state, iterator validity, and the mechanics of transfer operations.

To answer questions like this, you need to trace through the code carefully, keeping track of which container owns which elements at each step and how the relevant operations affect both the source and destination. Pay close attention to whether you're copying, moving, or using algorithms that reorder or clear containers. Interviewers use these questions to verify that you can reason about code behaviour without running it — a critical skill for writing reliable, high-performance systems.

• Move semantics and rvalue references
• Container state after assignment and swap operations
• Iterator invalidation rules
• Standard algorithms and their side effects on containers