C++ Interview Questions

Question 1

What is C++ and how differs from C?

Accepted Answer

C++ is an object-oriented extension of C adding classes, templates, STL, RAII, exceptions, and strong type safety. C++ adds: classes/objects, inheritance, polymorphism, templates (generics), STL containers/algorithms, RAII for resource management, exceptions, namespaces, references, operator overloading. Backward compatible with most C code. Modern C++ (11/14/17/20/23) has smart pointers, lambdas, ranges, concepts, modules.

Question 2

What is RAII (Resource Acquisition Is Initialization)?

Accepted Answer

RAII ties resource lifetime to object lifetime — resources acquired in constructor, released in destructor automatically. Example: std::unique_ptr automatically frees memory when scope ends. File handles in std::fstream close on destruction. Benefits: exception-safe, no resource leaks, deterministic cleanup. Foundation of modern C++ — prefer RAII over manual new/delete.

Question 3

What are smart pointers?

Accepted Answer

Smart pointers (unique_ptr, shared_ptr, weak_ptr) manage dynamic memory automatically, preventing leaks. unique_ptr: exclusive ownership, non-copyable, zero overhead. shared_ptr: reference-counted shared ownership. weak_ptr: non-owning observer of shared_ptr (breaks cycles). Use make_unique/make_shared. Prefer unique_ptr by default. Never use raw new/delete in modern C++.

Question 4

What are templates in C++?

Accepted Answer

Templates enable generic programming — write code once that works with any type, resolved at compile time. Function templates: template T max(T a, T b). Class templates: template class Stack. Template specialization for specific types. Variadic templates for variable arguments. SFINAE and concepts (C++20) for constraints. STL is built entirely on templates. Compile-time polymorphism.

Question 5

What is the STL?

Accepted Answer

Standard Template Library provides containers (vector, map), algorithms (sort, find), and iterators for generic programming. Containers: sequential (vector, deque, list, array), associative (map, set, multimap), unordered (unordered_map, unordered_set). Algorithms: sort, find, transform, accumulate, for_each. Iterators: connect containers and algorithms. C++20 ranges: lazy, composable alternative to iterator pairs.

Question 6

What is move semantics?

Accepted Answer

Move semantics transfer resources from temporary objects instead of copying, using rvalue references (&&) for performance. std::move casts to rvalue reference, enabling move constructor/assignment. Move constructor: steals resources, leaves source in valid but empty state. Rule of Five: if you define destructor/copy constructor/copy assignment, also define move constructor/move assignment. Eliminates expensive deep copies for temporaries.

Question 7

What are C++20 concepts?

Accepted Answer

Concepts constrain template parameters with readable requirements, replacing SFINAE with clear, expressive constraints. template concept Sortable = requires(T t) { std::sort(t.begin(), t.end()); }. Usage: template void mysort(T& container). Benefits: better error messages, readable constraints, documentation. Standard concepts: std::integral, std::floating_point, std::same_as, std::ranges::range.

Question 8

Your C++ application has performance issues. How to profile and optimize?

Accepted Answer

Profile with perf/Valgrind/VTune, identify hotspots, optimize algorithms, reduce copies, use move semantics and caching. Steps: (1) Profile: perf record/report, Valgrind --tool=callgrind, Intel VTune. (2) Optimize algorithms first (O(n²) → O(n log n)). (3) Reduce copies: pass by reference, use move semantics. (4) Cache-friendly data (SoA vs AoS). (5) Avoid virtual function calls in hot paths. (6) Use constexpr for compile-time computation. (7) Parallel algorithms (std::execution::par).

Question 9

Microsoft: What is the Rule of Five in C++?

Accepted Answer

If you define any of: destructor, copy constructor, copy assignment, move constructor, or move assignment — define all five. Managing resources (raw pointers, file handles) requires all five for correct behavior. Rule of Zero: prefer no custom resource management — use smart pointers and RAII containers. If a class owns a resource, implement all five. = default and = delete help express intent clearly.

Question 10

Free C++ Course - Learn OOP, STL & Modern C++ Programming

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Course Completion Certificate

Course Modules Overview

Introduction to C

Variables, Data Types & I/O

Control Flow & Functions

Object-Oriented Programming

Inheritance & Polymorphism

Templates & Generic Programming

Standard Template Library (STL)

Smart Pointers & Memory Management

Exception Handling & File I/O

C++ Project: Game Engine Basics

Modern CPP

CPP Career and Advanced Topics

Course Curriculum

Introduction to C

Variables, Data Types & I/O

Control Flow & Functions

Object-Oriented Programming

Inheritance & Polymorphism

Templates & Generic Programming

Standard Template Library (STL)

Smart Pointers & Memory Management

Exception Handling & File I/O

C++ Project: Game Engine Basics

Modern CPP

CPP Career and Advanced Topics

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Beginner

Intermediate

Advanced

Tools & Technologies

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