Modifying a buffer between reads

What this C++ standard-library question tests

This is a medium-difficulty C++ language question that probes your familiarity with modern stream abstractions, specifically the differences between traditional string-stream classes and newer span-based alternatives introduced in C++23. It rewards understanding both practical performance implications and the design intent behind the standard library's evolution.

To answer questions like this, you need to reason about memory ownership, buffer lifetime, and allocation overhead. The question asks you to observe code behavior and articulate a concrete technical advantage—a skill that matters in environments where efficiency and clarity of intent both count.

• String stream construction and copy semantics
• Non-owning views vs. owning containers
• Zero-copy patterns in C++
• Span-based library design (C++20 onwards)