The perfect union.

Understanding union initialization in C++

This medium-difficulty question tests your grasp of how unions behave under initialization in C++, a topic that appears frequently in low-latency trading systems where memory layout and bit-level control matter. The question asks you to trace through initialization semantics and predict the state of member variables.

To answer correctly, you need to understand the difference between value initialization, default initialization, and aggregate initialization for union types, as well as how the compiler handles overlapping storage. This knowledge is essential when working with packed data structures, network protocols, or hardware-level abstractions where unions are common.

• Union storage semantics and member overlap
• Initialization rules for aggregate types
• Uninitialized vs. zero-initialized state
• Compiler-dependent behavior and portability