Explain the rule of three, five and zero, plus undefined behaviour.
Assesses fundamental understanding of C++ conventions, runtime behavior, and memory/performance considerations.
Hiring managers look for precision, avoidance of ambiguous jargon, and ability to explain trade-offs under real production conditions.
The rule of three: if a class needs a custom destructor, copy constructor or copy assignment operator, it probably needs all three, because they manage the same resource. The compiler-generated copy does a shallow member-wise copy, so forgetting one causes double frees or leaks.
class Buf {
public:
~Buf(); // frees
Buf(const Buf&); // deep copy
Buf& operator=(const Buf&);
Buf(Buf&&) noexcept; // C++11 additions
Buf& operator=(Buf&&) noexcept;
};
The rule of five extends this to the move operations for efficiency. The rule of zero says the best design needs none of them: store resources in RAII members such as std::vector or unique_ptr and let the compiler generate correct operations.
Undefined behaviour means the standard imposes no requirements, so out-of-bounds access, use-after-free, signed overflow and data races let the optimiser do surprising things. Detect it with -Wall -Wextra, AddressSanitizer, UBSan and Valgrind rather than guessing.
Candidate Response Strategy & Interview Tips
- Start with a concise one-sentence summary: Deliver a direct, confident answer first before expanding into nuances.
- Demonstrate real-world trade-offs: Discuss where this approach excels and when you would avoid it in production systems.
- Discuss complexity & edge cases: Proactively explain time/space complexity or boundary conditions (null values, scale limits).
- Prepare for interviewer follow-ups: Technical hiring panels frequently probe deeper into concurrency, backward compatibility, or alternative libraries.