Filling a large vector with a small buffer

Understanding vector memory management in C++

This is a medium-difficulty C++ language-knowledge question that tests your grasp of how standard library containers manage memory behind the scenes. It asks you to trace through code involving vector operations and predict the output, which requires understanding the interaction between buffer allocation, capacity, and size.

To solve this kind of problem, you need to reason carefully about when vectors reallocate their underlying storage, how copy constructors and move semantics interact with that storage, and what values are actually accessible after each operation. Getting these details right matters in performance-critical code, where unnecessary reallocations or copies can silently tank throughput.

• Vector capacity vs. size semantics
• Memory reallocation and iterator invalidation
• Constructor and copy/move behaviour during growth