Top 10 Senior C++ Developer Interview Questions & Answers in 2024

1. Discuss the role and benefits of the Pimpl idiom in C++. Provide an example of when and how to use it.

The Pimpl idiom (Pointer to Implementation) is a design pattern in C++ where the implementation details of a class are hidden behind a pointer. This improves compilation times, encapsulation, and reduces dependencies. It's particularly useful when dealing with large and frequently changing codebases.

2. Explain the purpose and usage of the 'override' and 'final' keywords in C++.

The 'override' keyword in C++ is used to indicate that a member function in a derived class is intended to override a virtual function in the base class. It enhances code readability and catches errors during compilation. The 'final' keyword is used to prevent further overriding of a virtual function in derived classes, adding an extra layer of control in class hierarchies.

3. Describe the benefits and drawbacks of multiple inheritance in C++. Provide an example of a scenario where multiple inheritance is appropriate.

Multiple inheritance in C++ allows a class to inherit from more than one base class. It offers flexibility but can lead to the diamond problem and increased complexity. Use multiple inheritance when there is a clear "is-a" relationship between the derived class and multiple base classes, such as a class representing a FlyingCar inheriting from both Car and Airplane classes.

4. Discuss the purpose and usage of the 'constexpr' keyword in C++.

The 'constexpr' keyword in C++ is used to indicate that a variable or function can be evaluated at compile time. It enables performance improvements by moving computations from runtime to compile time. 'constexpr' is commonly used for constant expressions and is a crucial feature for template metaprogramming.

5. Explain the principles of the Rule of Three (Three Rule) in C++ and why it's important for resource management.

The Rule of Three states that if a class defines one of the following three functions (copy constructor, copy assignment operator, or destructor), it should define all three. This ensures proper resource management, especially when dealing with dynamically allocated memory. With the advent of C++11, this rule has evolved into the Rule of Five to include move constructor and move assignment operator.

6. Discuss the concept of SFINAE (Substitution Failure Is Not An Error) in C++ template metaprogramming. Provide an example of its application.

SFINAE is a principle in C++ where the compiler doesn't consider a substitution failure in a template specialization as an error. This allows templates to gracefully degrade when certain conditions are not met. An example is using SFINAE to enable or disable template specializations based on the presence or absence of a specific member function in a type.

7. Explain the differences between 'auto' and 'decltype' in C++, and when you would prefer one over the other.

'auto' is used for automatic type inference during variable initialization, while 'decltype' is used to deduce the type of an expression at compile time. Use 'auto' when the type is evident or when dealing with iterators, and 'decltype' when you want the type of an expression without creating an instance.

8. Describe the Observer design pattern in C++. Provide an example of its implementation.

The Observer pattern is a behavioral design pattern where an object, known as the subject, maintains a list of dependents, known as observers, that are notified of any state changes. An example is implementing a GUI button with multiple subscribers (observers) that react to the button's click event.

9. Discuss the benefits of using smart pointers over raw pointers in modern C++. Provide examples of smart pointer types and their use cases.

Smart pointers, such as std::unique_ptr and std::shared_ptr, manage memory automatically, preventing memory leaks and improving code safety. Use std::unique_ptr for exclusive ownership and std::shared_ptr for shared ownership. Smart pointers simplify memory management, enhance code readability, and reduce the risk of memory-related bugs.

10. Explore the use of the 'consteval' keyword in C++20. How does it differ from 'constexpr'?

The 'consteval' keyword in C++20 extends the capabilities of 'constexpr' by ensuring that a function or a part of a function must be evaluated at compile time. It provides stronger guarantees for compile-time evaluation compared to 'constexpr'. 'consteval' is used to enforce compile-time evaluations for specific functions, offering more control over constant expressions.