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What this C++ language-knowledge question tests

This is a hard C++ question that probes deep familiarity with the evolution of the language standard. It requires you to reason about how a specific code snippet behaves under pre-C++17 semantics, and implicitly to understand what changed in C++17 that would alter that behaviour.

Questions like this appear in interviews at firms where C++ expertise is non-negotiable—particularly in low-latency trading and systems work. They test whether you understand not just how to write code that works, but the underlying rules that govern language behaviour across versions. Success depends on tracing through the code mentally under the older standard's rules, which often differ subtly from modern C++.

• C++ standard evolution and breaking changes
• Semantic differences between language versions
• Reading and predicting code behaviour without running it