Ошибка	Последствие
`std::move` от `const`-объекта	Тихо выбирается copy-ctor, перемещения не происходит, без warnings
Использование объекта после `std::move`	Чтение valid-but-unspecified-состояния → непредсказуемые значения
Move-конструктор без `noexcept`	`std::vector` при realloc копирует вместо move — выигрыш от move потерян
`return std::move(v)` для локальной переменной	Блокирует NRVO: гарантированный move вместо «вообще ничего»
Использование `b` как rvalue после `void f(T&& b)`	`b` — lvalue-выражение; нужен `std::move(b)` или `std::forward<T>(b)`
`std::forward<T>` вне шаблонной функции	Всегда даёт rvalue — лучше написать `std::move` напрямую
Объявить только move-ctor, ожидая работающий copy	Copy неявно удалён — компилятор выдаст ошибку только в месте использования
Объявить пользовательский деструктор, ожидать сгенерированный move	Move подавлен; принудительный move молча превращается в copy

intermediate

Move Semantics

Rvalue references, move constructors, move assignment, std::move, and std::forward — transferring ownership without unnecessary copies.

MoveSemanticsintroduced c++11move-semantics

Practice: 26 questions →

Sections

Contents

Detailed explanation

Move Semantics — transferring ownership instead of copying

Before C++11, passing or returning a large object meant copying it: returning std::vector from a function — copy; inserting a string into a container — copy. Each copy allocates memory, walks the bytes, and frees the source. Move semantics fixes this: if the source is a temporary or has explicitly released its resource, the receiver transfers ownership instead of duplicating. For std::vector that means stealing the internal pointer — O(1) instead of O(n).

In C++, move sits across several mechanisms: a new value category (xvalue), a new reference kind (T&&), std::move as a cast, move constructors and assignment, the noexcept contract, copy elision, and forwarding references in templates. Traps: std::move on const, a named T&& being an lvalue, return std::move(v) blocking NRVO, missing noexcept disabling moves in std::vector.

Topic map

Value categories — lvalue, rvalue, prvalue, xvalue, glvalue — what can be moved and why.
Rvalue references — T&&, the named-parameter rule, reference collapsing.
std::move and moved-from state — std::move as a cast; valid-but-unspecified; the const trap.
Move constructor and Rule of Five — T(T&&) noexcept, the suppression rule, Rule of Zero/Five.
Perfect forwarding — std::forward, forwarding references, std::move vs std::forward.
Copy elision (RVO/NRVO) — when no move is needed; why return std::move(v) is worse than return v.
Move-only types — unique ownership via = delete on copy: std::unique_ptr, std::thread.

Common traps

Mistake	Consequence
`std::move` on a `const` object	Silently picks copy-ctor; no move, no warning
Using an object after `std::move`	Reading the valid-but-unspecified state → unpredictable values
Move constructor without `noexcept`	`std::vector` realloc falls back to copying — move benefit lost
`return std::move(v)` for a local	Blocks NRVO: guaranteed move instead of "nothing at all"
Treating `b` as rvalue after `void f(T&& b)`	`b` is an lvalue expression; needs `std::move(b)` or `std::forward<T>(b)`
`std::forward<T>` outside a template	Always yields rvalue — just write `std::move`
Declaring only move-ctor, expecting copy to work	Copy is implicitly deleted; the compiler errors at the call site
Declaring a user destructor, expecting generated move	Move suppressed; a forced move silently falls back to copy

Interview relevance

Move semantics is one of the most reliable middle/senior C++ interview topics. Interviewers check whether you understand why each piece works the way it does, not syntax.

The most common wrong answer: "std::move moves the object". It does not. It is a cast. The move constructor moves.

What the interviewer is actually checking:

Understanding of value categories — lvalue/prvalue/xvalue/glvalue.
Why a named T&& parameter in the body is an lvalue expression.
std::move vs std::forward — when and why.
Moved-from state: valid but unspecified.
The functional role of noexcept on move (std::vector realloc).
RVO/NRVO and why return std::move(v) is worse than return v.
std::move on const — silent copy.

Common questions:

What does std::move do? Move or cast?
What state is the source in after std::move?
Why mark the move constructor noexcept?
How does std::move differ from std::forward?
What is a forwarding reference, and how is it different from a plain T&&?
Explain RVO/NRVO and guaranteed copy elision.
Why does std::move on a const not move?

Why it matters

Move semantics is one of the main reasons modern C++ can express ownership and stay efficient at the same time. It is also a frequent interview topic at the middle and senior level.

Ошибка	Последствие
`std::move` от `const`-объекта	Тихо выбирается copy-ctor, перемещения не происходит, без warnings
Использование объекта после `std::move`	Чтение valid-but-unspecified-состояния → непредсказуемые значения
Move-конструктор без `noexcept`	`std::vector` при realloc копирует вместо move — выигрыш от move потерян
`return std::move(v)` для локальной переменной	Блокирует NRVO: гарантированный move вместо «вообще ничего»
Использование `b` как rvalue после `void f(T&& b)`	`b` — lvalue-выражение; нужен `std::move(b)` или `std::forward<T>(b)`
`std::forward<T>` вне шаблонной функции	Всегда даёт rvalue — лучше написать `std::move` напрямую
Объявить только move-ctor, ожидая работающий copy	Copy неявно удалён — компилятор выдаст ошибку только в месте использования
Объявить пользовательский деструктор, ожидать сгенерированный move	Move подавлен; принудительный move молча превращается в copy

intermediate

Move Semantics

Rvalue references, move constructors, move assignment, std::move, and std::forward — transferring ownership without unnecessary copies.

MoveSemanticsintroduced c++11move-semantics

Practice: 26 questions →

Sections

Contents

Detailed explanation

Move Semantics — transferring ownership instead of copying

Topic map

Value categories — lvalue, rvalue, prvalue, xvalue, glvalue — what can be moved and why.
Rvalue references — T&&, the named-parameter rule, reference collapsing.
std::move and moved-from state — std::move as a cast; valid-but-unspecified; the const trap.
Move constructor and Rule of Five — T(T&&) noexcept, the suppression rule, Rule of Zero/Five.
Perfect forwarding — std::forward, forwarding references, std::move vs std::forward.
Copy elision (RVO/NRVO) — when no move is needed; why return std::move(v) is worse than return v.
Move-only types — unique ownership via = delete on copy: std::unique_ptr, std::thread.

Common traps

Mistake	Consequence
`std::move` on a `const` object	Silently picks copy-ctor; no move, no warning
Using an object after `std::move`	Reading the valid-but-unspecified state → unpredictable values
Move constructor without `noexcept`	`std::vector` realloc falls back to copying — move benefit lost
`return std::move(v)` for a local	Blocks NRVO: guaranteed move instead of "nothing at all"
Treating `b` as rvalue after `void f(T&& b)`	`b` is an lvalue expression; needs `std::move(b)` or `std::forward<T>(b)`
`std::forward<T>` outside a template	Always yields rvalue — just write `std::move`
Declaring only move-ctor, expecting copy to work	Copy is implicitly deleted; the compiler errors at the call site
Declaring a user destructor, expecting generated move	Move suppressed; a forced move silently falls back to copy

Interview relevance

Move semantics is one of the most reliable middle/senior C++ interview topics. Interviewers check whether you understand why each piece works the way it does, not syntax.

The most common wrong answer: "std::move moves the object". It does not. It is a cast. The move constructor moves.

What the interviewer is actually checking:

Understanding of value categories — lvalue/prvalue/xvalue/glvalue.
Why a named T&& parameter in the body is an lvalue expression.
std::move vs std::forward — when and why.
Moved-from state: valid but unspecified.
The functional role of noexcept on move (std::vector realloc).
RVO/NRVO and why return std::move(v) is worse than return v.
std::move on const — silent copy.

Common questions:

What does std::move do? Move or cast?
What state is the source in after std::move?
Why mark the move constructor noexcept?
How does std::move differ from std::forward?
What is a forwarding reference, and how is it different from a plain T&&?
Explain RVO/NRVO and guaranteed copy elision.
Why does std::move on a const not move?

Why it matters

Move semantics is one of the main reasons modern C++ can express ownership and stay efficient at the same time. It is also a frequent interview topic at the middle and senior level.

Move-семантика

Move-семантика — передача владения вместо копирования

Карта темы

Частые ошибки и ловушки

Значение для собеседований

Move Semantics

Move Semantics — transferring ownership instead of copying

Topic map

Common traps

Interview relevance

Move-семантика

Move-семантика — передача владения вместо копирования

Карта темы

Частые ошибки и ловушки

Значение для собеседований

Move Semantics

Move Semantics — transferring ownership instead of copying

Topic map

Common traps

Interview relevance