C++ Developer Interview Questions UK: 8 Real Questions and What Interviewers Want

Most C++ Developer interviews in the UK follow a pattern, and knowing it beats guessing. Below are eight questions from our bank of 16, each with a note on what the interviewer is really after.

Eight C++ Developer interview questions, and what the interviewer is thinking

1. Can you explain RAII and how smart pointers such as unique_ptr and shared_ptr support it?

Why they ask: Resource management is the heart of idiomatic modern C++.

2. What is move semantics, and what is the difference between an lvalue and an rvalue reference?

Why they ask: Move semantics are a defining feature of C++11 onwards and affect performance directly.

3. How do virtual functions work, and why should a base class destructor be virtual?

Why they ask: It tests understanding of polymorphism and a classic source of undefined behaviour.

4. Explain the differences between std::vector, std::list, std::map and std::unordered_map, and how you decide between them.

Why they ask: Container choice has a major effect on performance and clarity.

5. How do you write thread-safe C++ code? What tools does the standard library give you?

Why they ask: Concurrency bugs are expensive, so employers test for careful reasoning.

6. Your application crashes intermittently in production, and you cannot reproduce it locally. What do you do?

Why they ask: It tests structured debugging of the hardest class of C++ faults.

7. Tell me about a time you tracked down a difficult bug in C++ code.

Why they ask: They want evidence of persistence and a methodical debugging process.

8. Why do you want to work as a C++ developer, and what kind of projects interest you?

Why they ask: They want to understand your motivation and fit with the domain.

A sample answer to question 1

Can you explain RAII and how smart pointers such as unique_ptr and shared_ptr support it?

RAII means a resource's lifetime is tied to an object's lifetime: the constructor acquires it and the destructor releases it, so cleanup happens automatically when the object goes out of scope, even if an exception is thrown. Smart pointers apply that to heap memory. std::unique_ptr expresses sole ownership, is move-only and has no overhead compared with a raw pointer, so it's my default. std::shared_ptr uses reference counting for shared ownership, which costs an atomic counter and can create leaks through cycles, so I break cycles with std::weak_ptr. I create them with make_unique and make_shared, which are exception-safe, and I pass raw pointers or references to functions that merely use an object without owning it. The same principle covers lock_guard for mutexes, file handles and sockets, so I almost never write a manual delete.

Common mistake to avoid: Using new and delete in modern code; using shared_ptr everywhere by habit

Want the rest?

Full model answers, key points and common mistakes for all 16 questions are on the C++ Developer interview questions page. The first five are free, no sign-up needed.