Allocating from a small arena buffer

What this C++ memory-allocation question tests

This is a medium-difficulty C++ question that probes your understanding of stack-based memory management and how arena allocators work in practice. It asks you to trace through code that uses a small fixed buffer and predict the program's output—a common pattern in low-latency systems where heap allocation is avoided.

To answer correctly, you need to understand how memory is carved out of a pre-allocated region, how pointers and offsets behave, and what happens when allocations are made sequentially from a fixed arena. The question rewards careful attention to initialization, pointer arithmetic, and the actual bytes being written and read.

• Stack vs. heap allocation trade-offs
• Pointer arithmetic and address calculation
• Memory layout and alignment
• Arena allocator semantics