Where did the arena go?

Understanding scope and lifetime in C++ memory management

This hard C++ question tests your grasp of object lifetime and scope rules — specifically, what happens when a memory arena or custom allocator falls out of scope while pointers to its allocations remain in use. It is the kind of subtle semantics issue that separates candidates who memorize syntax from those who truly understand the language's memory model.

To answer correctly, you must trace the execution flow, identify when objects are constructed and destroyed, and reason about the validity of pointers after their backing storage has been deallocated. The question rewards careful attention to order of destruction, scope boundaries, and the difference between dangling pointers and use-after-free.

• Stack vs. heap allocation and automatic cleanup
• Destructor ordering and scope exit
• Undefined behaviour from invalid memory access
• RAII principles and resource ownership