C++ Interview Questions and Answers

Answer: General-purpose programming language with low-level access

C++ is a general-purpose programming language created by Bjarne Stroustrup. It provides low-level memory access with high-level abstractions and object-oriented features.

Answer: Transfers resources instead of copying

Move semantics transfers resources instead of copying. Uses rvalue references (&&). Move constructor and move assignment operator. Improves performance for temporary objects.

Answer: Standard Template Library with containers, algorithms, iterators

STL (Standard Template Library) provides containers (vector, map, set), algorithms (sort, find), and iterators. Built on templates for type safety and efficiency.

Answer: Blueprint for generic programming

Templates enable generic programming. Define functions/classes that work with any type. Compiler generates type-specific code. Two types: function templates and class templates.

Answer: Reference to temporary object (&&)

Rvalue reference (&&) binds to temporary objects (rvalues). Enables move semantics and perfect forwarding. Distinguishes from lvalue references (&). C++11 feature.

Answer: C++ adds OOP, templates, STL to C

C++ extends C with object-oriented programming, templates, STL, better type checking, function overloading, references, and many modern features.

Answer: Dynamic array that grows/shrinks automatically

vector is a dynamic array that automatically grows/shrinks. Contiguous memory. Random access. Use push_back(), pop_back(), size(). Include <vector>.

Answer: main()

The main() function is the entry point of every C++ program. Execution starts from main(). Returns int, typically 0 for success.

Answer: Casts lvalue to rvalue reference

std::move casts lvalue to rvalue reference, enabling move semantics. Doesn't actually move anything. Indicates object can be moved from. Use with caution.

Answer: Forwards arguments preserving value category

Perfect forwarding preserves argument value category (lvalue/rvalue). Uses forwarding references (T&&) and std::forward. Essential for generic code, wrappers.

Answer: Associative container of key-value pairs

map is an associative container storing sorted key-value pairs. Implemented as red-black tree. Keys unique. O(log n) operations. Include <map>.

Answer: Includes input/output stream library for cin/cout

#include <iostream> includes the input/output stream library, providing cin (input), cout (output), cerr (error), and clog (logging).

Answer: RAII wrapper managing pointer lifetime automatically

Smart pointers are RAII wrappers managing pointer lifetime automatically. Types: unique_ptr (exclusive ownership), shared_ptr (shared ownership), weak_ptr (non-owning). Prevent leaks.

Answer: Declarative region preventing name conflicts

Namespace is a declarative region providing scope for identifiers. Prevents name conflicts. std is the standard library namespace. Use using namespace std; or std::.

Answer: map sorted (tree), unordered_map unsorted (hash)

map is sorted (red-black tree, O(log n)). unordered_map is hash table (O(1) average). Use map for ordered iteration, unordered_map for faster lookup.

Answer: Output stream object for printing to console

cout is the standard output stream object. Use with << operator for output: cout << "Hello". Part of iostream library in std namespace.

Answer: Smart pointer with exclusive ownership

unique_ptr has exclusive ownership. Cannot be copied, only moved. Lightweight, no overhead. Use make_unique. Default choice for smart pointers.

Answer: Object for traversing containers

Iterator is an object for traversing containers. Acts like pointer. Types: begin(), end(), rbegin(), rend(). Use with ++, --, *, ->. Generic way to access elements.

Answer: Smart pointer with shared ownership via reference counting

shared_ptr shares ownership via reference counting. Object deleted when last shared_ptr destroyed. Overhead from ref count. Use make_shared. Watch for cycles.

Answer: Mechanism for creating class from existing class

Inheritance creates new class (derived/child) from existing class (base/parent). Promotes code reuse. Supports is-a relationship. Types: single, multiple, multilevel, hierarchical.

Answer: Input stream object for reading from console

cin is the standard input stream object. Use with >> operator for input: cin >> variable. Reads from standard input (keyboard).

Answer: Non-owning reference breaking shared_ptr cycles

weak_ptr is non-owning reference to shared_ptr. Doesn't increase ref count. Prevents cycles. Convert to shared_ptr with lock(). Check validity with expired().

Answer: Objects of different types accessed through common interface

Polymorphism allows objects of different types to be accessed through common interface. Achieved via virtual functions. Enables runtime polymorphism (dynamic binding).

Answer: Named storage location with specific type

A variable is a named storage location with a specific data type. Must be declared before use: int x = 5; Type determines size and operations.