Rearranging members of two structures

Understanding struct memory layout and alignment in C++

This is a medium-difficulty question that tests your knowledge of how C++ arranges data members in memory, a topic quant firms care about because it directly affects cache efficiency, serialization, and low-latency code. The question requires you to reason about struct padding and alignment rules on a 64-bit platform.

To answer correctly, you need to understand that the compiler does not simply pack members sequentially. Instead, it respects alignment requirements: each member must be positioned so its address is a multiple of its own size (or the alignment requirement set by the platform). This often introduces invisible padding bytes between members, and the total struct size may exceed the sum of its parts. The order in which you declare members directly affects how much padding is inserted.

• Alignment requirements for primitive types (int, double, etc.)
• Padding insertion between and after struct members
• How member declaration order affects total struct size
• Platform-specific sizeof() behavior