Comparing layouts of empty member pairs

What this C++ memory layout question tests

This is a hard C++ language-knowledge question that probes your understanding of struct padding, member ordering, and object layout in memory. It requires you to reason precisely about how the compiler allocates space for class members, including the handling of empty types.

To answer correctly, you need to know the rules governing alignment requirements, how the compiler packs or separates members, and what happens when a struct contains members of zero size. This skill matters in systems programming, performance-critical code, and anywhere memory layout affects correctness or efficiency. The question rewards careful attention to C++ standard behavior rather than guesswork.

• Alignment and padding rules for struct members
• Empty member optimization and the empty base optimization (EBO)
• How sizeof() reflects layout decisions
• Compiler-dependent vs. standard-mandated behavior