c assignment operator vector

• <cassert> (assert.h)
• <cctype> (ctype.h)
• <cerrno> (errno.h)
• C++11 <cfenv> (fenv.h)
• <cfloat> (float.h)
• C++11 <cinttypes> (inttypes.h)
• <ciso646> (iso646.h)
• <climits> (limits.h)
• <clocale> (locale.h)
• <cmath> (math.h)
• <csetjmp> (setjmp.h)
• <csignal> (signal.h)
• <cstdarg> (stdarg.h)
• C++11 <cstdbool> (stdbool.h)
• <cstddef> (stddef.h)
• C++11 <cstdint> (stdint.h)
• <cstdio> (stdio.h)
• <cstdlib> (stdlib.h)
• <cstring> (string.h)
• C++11 <ctgmath> (tgmath.h)
• <ctime> (time.h)
• C++11 <cuchar> (uchar.h)
• <cwchar> (wchar.h)
• <cwctype> (wctype.h)

Containers:

• C++11 <array>
• <deque>
• C++11 <forward_list>
• <list>
• <map>
• <queue>
• <set>
• <stack>
• C++11 <unordered_map>
• C++11 <unordered_set>
• <vector>

Input/Output:

• <fstream>
• <iomanip>
• <ios>
• <iosfwd>
• <iostream>
• <istream>
• <ostream>
• <sstream>
• <streambuf>

Multi-threading:

• C++11 <atomic>
• C++11 <condition_variable>
• C++11 <future>
• C++11 <mutex>
• C++11 <thread>
• <algorithm>
• <bitset>
• C++11 <chrono>
• C++11 <codecvt>
• <complex>
• <exception>
• <functional>
• C++11 <initializer_list>
• <iterator>
• <limits>
• <locale>
• <memory>
• <new>
• <numeric>
• C++11 <random>
• C++11 <ratio>
• C++11 <regex>
• <stdexcept>
• <string>
• C++11 <system_error>
• C++11 <tuple>
• C++11 <type_traits>
• C++11 <typeindex>
• <typeinfo>
• <utility>
• <valarray>
• vector<bool>
• vector::~vector
• vector::vector

member functions

• vector::assign
• vector::back
• vector::begin
• vector::capacity
• C++11 vector::cbegin
• C++11 vector::cend
• vector::clear
• C++11 vector::crbegin
• C++11 vector::crend
• C++11 vector::data
• C++11 vector::emplace
• C++11 vector::emplace_back
• vector::empty
• vector::end
• vector::erase
• vector::front
• vector::get_allocator
• vector::insert
• vector::max_size
• vector::operator[]
• vector::operator=
• vector::pop_back
• vector::push_back
• vector::rbegin
• vector::rend
• vector::reserve
• vector::resize
• C++11 vector::shrink_to_fit
• vector::size
• vector::swap

non-member overloads

• relational operators (vector)
• swap (vector)

std:: vector ::operator=

Return value

Iterator validity

Exception safety.

21.12 — Overloading the assignment operator

This browser is no longer supported.

Upgrade to Microsoft Edge to take advantage of the latest features, security updates, and technical support.

Move Constructors and Move Assignment Operators (C++)

• 9 contributors

This topic describes how to write a move constructor and a move assignment operator for a C++ class. A move constructor enables the resources owned by an rvalue object to be moved into an lvalue without copying. For more information about move semantics, see Rvalue Reference Declarator: && .

This topic builds upon the following C++ class, MemoryBlock , which manages a memory buffer.

The following procedures describe how to write a move constructor and a move assignment operator for the example C++ class.

To create a move constructor for a C++ class

Define an empty constructor method that takes an rvalue reference to the class type as its parameter, as demonstrated in the following example:

In the move constructor, assign the class data members from the source object to the object that is being constructed:

Assign the data members of the source object to default values. This prevents the destructor from freeing resources (such as memory) multiple times:

To create a move assignment operator for a C++ class

Define an empty assignment operator that takes an rvalue reference to the class type as its parameter and returns a reference to the class type, as demonstrated in the following example:

In the move assignment operator, add a conditional statement that performs no operation if you try to assign the object to itself.

In the conditional statement, free any resources (such as memory) from the object that is being assigned to.

The following example frees the _data member from the object that is being assigned to:

Follow steps 2 and 3 in the first procedure to transfer the data members from the source object to the object that is being constructed:

Return a reference to the current object, as shown in the following example:

Example: Complete move constructor and assignment operator

The following example shows the complete move constructor and move assignment operator for the MemoryBlock class:

Example Use move semantics to improve performance

The following example shows how move semantics can improve the performance of your applications. The example adds two elements to a vector object and then inserts a new element between the two existing elements. The vector class uses move semantics to perform the insertion operation efficiently by moving the elements of the vector instead of copying them.

This example produces the following output:

Before Visual Studio 2010, this example produced the following output:

The version of this example that uses move semantics is more efficient than the version that does not use move semantics because it performs fewer copy, memory allocation, and memory deallocation operations.

Robust Programming

To prevent resource leaks, always free resources (such as memory, file handles, and sockets) in the move assignment operator.

To prevent the unrecoverable destruction of resources, properly handle self-assignment in the move assignment operator.

If you provide both a move constructor and a move assignment operator for your class, you can eliminate redundant code by writing the move constructor to call the move assignment operator. The following example shows a revised version of the move constructor that calls the move assignment operator:

The std::move function converts the lvalue other to an rvalue.

Rvalue Reference Declarator: && std::move

Was this page helpful?

Additional resources

Stack Exchange Network

Stack Exchange network consists of 183 Q&A communities including Stack Overflow , the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Q&A for work

Connect and share knowledge within a single location that is structured and easy to search.

Vector with move constructor and move assignment operator [closed]

Please verify whether the code for a move constructor and a move assignment operator is correct.

• memory-management

• \$\begingroup\$ This isn't that kind of code review; take the tour , see How to Ask . If you aren't certain it works, test it. \$\endgroup\$ –  jonrsharpe Commented Apr 2, 2017 at 8:54

Default constructor

Stop trying to save space like that. THe point of good coding is to make it readable by humans. The computer can read any style so try and make it more maintainable by making it readable.

I would write it like this:

Sure you can use nullptr for the zero sized array. But this seems like a premature optimization. You can make the rest of your code less complicated by never having a null m_pInt . If there is never a null then your code does not need to check for it.

Also currently you have different behavior for:

Constructor

Sure this works. But std::cout is not the only stream you way want to print too

So I would pass a stream to print() . It can default to std::cout . Then you should add an operator<< . As the normal way of printing something is via << .

Note: prefer "\n" to std::endl . The difference is a stream flush. The stream will already flush itself when required. So you adding extra flushes is only going to cause the flushes to be less optimal.

Copy Constructor

Move constructor.

Yes that works. But you should also mark the move constructor as noexcept . The standard containers have optimizations that can be applied if they know tour class will not throw when being moved. Otherwise they have to fallback to copying to provide the strong exception guarantee.

The standard technique is to use swap though. It makes it look and behave just like move assignment. See below.

Copy Assignment

Yes the test for self assignment looks like a good optimization.

BUT its not. Self assignment happens so rarely (in fact basically never in real code) that what you are doing is pesimizing the normal flow and as a result will make your code slower. You do need to cope with self assignment but because it is so rare you don't need to worry that it is not the optimal path.

The second issue I have here is that you destroy the local data before you have a copy of the new data ready.

If something goes wrong in the rest of your code then you will be unable to roll back the state and thus can not provide the strong exception guarantee. When copying an object it should happen in three distict phases.

So your Copy assignment should look like this:

If you look carefully at those three stages. Stage 1 looks like the constructor and stage 3 looks like the destructor and stage 2 looks like a standard swap function so we can simplify the above to exactly that:

This is called the copy and swap idiom.

Move Assignment

Again the pesimizing test for self assignment.

The standard move assignment is to swap the source and the destination. This has a couple of benefits.

• You don't call delete (and thus don't invoke the destructor). Thus it is potentially faster.
• Because you did not delete the data there is an opportunity for it to be reused.
• If the source is going out of scope it will invoke its destructor and destroy your data but it will be done after the completion of your object thus giving you strong exception guarantee. Thus allowing you to make your assignment operator noexcept.

Standard Move Assignment

I wrote a series of posts about all this.

Vector - Resource Management Allocation Vector - Resource Management Copy Swap Vector - Resize Vector - Simple Optimizations Vector - the Other Stuff

• \$\begingroup\$ Hi. What do you mean by "Stop trying to save space like that." regarding the code MyVector():m_Size(0), m_pInt(nullptr) { } ? What would you write instead if this was the only constructor? \$\endgroup\$ –  krismath Commented May 1, 2017 at 21:20
• 2 \$\begingroup\$ @krismath: One initialization per line. The point is to write readable code not try and squeeze as many operations onto a single line as you can. Updating answer with how I would write it. \$\endgroup\$ –  Loki Astari Commented May 1, 2017 at 23:03
• \$\begingroup\$ MyVector() could be noexcept if you allow for m_pInt being nullptr . That's worth the hassle easily. \$\endgroup\$ –  Deduplicator Commented May 1, 2017 at 23:16
• 1 \$\begingroup\$ @Deduplicator Not sure a noexcept default constructor buys you anything. Are there any optimizations in the STL this will enable? If it does not gain you anything then why add the extra complexity to the rest of your code. Especially when it adds two different meanings for basically the same declaration MyVector x; /* nullptr but size 0*/ and MyVector y(0); /* Not nullptr but size 0*/ \$\endgroup\$ –  Loki Astari Commented May 1, 2017 at 23:31
• \$\begingroup\$ Fantastic answer. 1. I wonder why didn't you add m_pInt = nullptr in the destructor after deleting it. Omission? 2. In the ctor: MyVector(int x = 0) : m_size(0) . I believe you wanted to say m_size(x) here right? 3. I always tend to use {} instead of () for initialization of objects because it prevents widening and is more readable (doesn't look like a function call). \$\endgroup\$ –  KeyC0de Commented Oct 19, 2018 at 3:47

Not the answer you're looking for? Browse other questions tagged c++ c++11 memory-management vectors or ask your own question .

• The Overflow Blog
• From PHP to JavaScript to Kubernetes: how one backend engineer evolved over time
• Featured on Meta
• We've made changes to our Terms of Service & Privacy Policy - July 2024
• Bringing clarity to status tag usage on meta sites

Hot Network Questions

• Group automorphism fixing finite-index subgroup
• Help Identify SMD IC Component Marking 9HH or D9HH
• Are there any rockets that leave extra fuel as a backup?
• What are the limits of Terms of Service as a legal shield for a company?
• How do you hide an investigation of alien ruins on the moon during Apollo 11?
• Why are volumes of revolution typically taught in Calculus 2 and not Calculus 3?
• Dual-555 servo controller: how to "stabilize" without two separate voltage regulators?
• If physics can be reduced to mathematics (and thus to logic), does this mean that (physical) causation is ultimately reducible to implication?
• Is the error in translation of Genesis 19:5 deliberate?
• Unexpected behavior of SetDelayed and Derivative
• Uppercase “God” in translations of Greek plays
• Time dilation with variable time scale
• Is there anything that stops the majority shareholder(s) from destroying company value?
• Seth and Cain take turns picking numbers from 1 to 50. Who wins?
• Reduce String Length With Thread Safety & Concurrency
• In theory, could an object like 'Oumuamua have been captured by a three-body interaction with the sun and planets?
• R Squared Causal Inference
• Is it possible to create a board position where White must make the move that leads to stalemating Black to avoid Black stalemating White?
• Why is not it generally accepted that tyranids are the strongest most adaptable race in w40k?
• Which class is the language MAX-CLIQUE in?
• Picture inside the proof environment
• A simplified Blackjack C++ OOP console game
• Op Amp Feedback Resistors
• Do cities usually form at the mouth of rivers or closer to the headwaters?

• C++ Data Types
• C++ Input/Output
• C++ Pointers
• C++ Interview Questions
• C++ Programs
• C++ Cheatsheet
• C++ Projects
• C++ Exception Handling
• C++ Memory Management

Move Assignment Operator in C++ 11

In C++ programming, we have a feature called the move assignment operator, which was introduced in C++11. It helps us handle objects more efficiently, especially when it comes to managing resources like memory. In this article, we will discuss move assignment operators, when they are useful and called, and how to create user-defined move assignment operators.

Move Assignment Operator

The move assignment operator was added in C++ 11 to further strengthen the move semantics in C++. It is like a copy assignment operator but instead of copying the data, this moves the ownership of the given data to the destination object without making any additional copies. The source object is left in a valid but unspecified state.

User-Defined Move Assignment Operator

The programmer can define the move assignment operator using the syntax given below:

As you may have noticed, the move assignment operator function uses a special && reference qualifier. It represents the r-value references (generally literals or temporary values).

Usually, it returns a reference to the object (in this case, *this) so you can chain assignments together.

The move constructor is called by the compiler when the argument is an rvalue reference which can be done by std::move() function. 

Example of Move Assignment Operator

In this program, we will create a dynamic array class and create a user-defined move assignment operator.

Explanation

The move assignment operator (operator=) is used to transfer resources from one DynamicArray object to another. It releases the current resources of the destination object, takes the resources from the source object, and leaves the source object in a valid but unspecified state.

In the main function:

• We create two DynamicArray objects, arr1 with 5 elements and arr2 with 10 elements. We print their initial states.
• We use the move assignment operator to transfer the resources from arr1 to arr2 by calling arr2 = std::move(arr1).
• After the move, we print the states of both arr1 and arr2. arr1 is now in a valid but unspecified state, and arr2 contains the resources of arr1.

Note: We can also define a move constructor with a move assignment operator and reduce the code redundancy by calling the move assignment operator from the move constructor. To know about move constructor, refer to the article – Move Constructors in C++

Implicit Definition of Move Assignment Operator

The compiler also defines a default move assignment operator implicitly when the following conditions are satisfied:

• No user-defined copy constructor is present.
• No user-defined destructor is present.
• No user-defined move constructor is present.

Need of Move Assignment Operator

In C++, objects can manage resources like memory. When we copy an object, it can be quite slow, especially if the object holds a lot of resources. Traditional copy operations create new copies, which can lead to unnecessary memory usage and slow down your program.

This is where move assignment operators come to the rescue. They let one object take over the resources of another, without making extra copies. This can significantly boost performance in scenarios like resizing arrays or returning objects from functions.

In contrast to the copy assignment operator, the end result of the move assignment operator will be a single copy of the source object.

Please Login to comment...

Similar reads.

• Geeks Premier League
• Geeks Premier League 2023
• How to Get a Free SSL Certificate
• Best SSL Certificates Provider in India
• Elon Musk's xAI releases Grok-2 AI assistant
• What is OpenAI SearchGPT? How it works and How to Get it?
• Content Improvement League 2024: From Good To A Great Article

Improve your Coding Skills with Practice

What kind of Experience do you want to share?

• Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers
• Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand
• OverflowAI GenAI features for Teams
• OverflowAPI Train & fine-tune LLMs
• Labs The future of collective knowledge sharing
• About the company Visit the blog

Collectives™ on Stack Overflow

Find centralized, trusted content and collaborate around the technologies you use most.

Q&A for work

Connect and share knowledge within a single location that is structured and easy to search.

Get early access and see previews of new features.

Overloading assignment operator with Classes and Vectors

I have a class defined:

and am trying to overload the assignment operator by such:

and I get the error code that buf is protected and length is protected. I'm not sure what I am missing. How can I properly overload the assignment operator with vectors and ints ?

• operator-overloading

• 1 The implicitly-generated assignment operator does the same thing, so if you don't have anything else in the function besides what you have shown here then it'd be better to not define it yourself (or define as default in C++11) –  M.M Commented Aug 5, 2014 at 5:21

2 Answers 2

You do not need to provide any special member functions for your class, because the compiler synthesized ones will do the right thing in this case. The best option is to remove the assignment operator and copy constructor from your class definition.

You need to define the implementation as part of the class. You are missing the class specifier:

As written, you are defining a free operator overload (not bound to a class), and it's actually invalid to declare a free assignment operator overload anyway.

From the perspective of a free operator overload that isn't a member of String , buf and length are indeed inaccessible because they are private.

Your Answer

Reminder: Answers generated by artificial intelligence tools are not allowed on Stack Overflow. Learn more

Sign up or log in

Post as a guest.

Required, but never shown

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy .

Not the answer you're looking for? Browse other questions tagged c++ vector operator-overloading or ask your own question .

• The Overflow Blog
• From PHP to JavaScript to Kubernetes: how one backend engineer evolved over time
• Featured on Meta
• We've made changes to our Terms of Service & Privacy Policy - July 2024
• Bringing clarity to status tag usage on meta sites
• What does a new user need in a homepage experience on Stack Overflow?
• Feedback requested: How do you use tag hover descriptions for curating and do...

Hot Network Questions

• Reduce String Length With Thread Safety & Concurrency
• Distribute realized geometry based on field values
• Why the mediating particle of gravity has different spin than that of the other forces?
• Idiomatic alternative to “going to Canossa”
• Vector of integers such that almost all dot products are positive
• CCTV control box connector
• Meaning of “ ’thwart” in a 19th century poem
• Help Identify SMD IC Component Marking 9HH or D9HH
• Are automorphisms of matrix algebras necessarily determinant preservers?
• If the Collatz conjecture is undecidable, then it is true
• Is there any reason for the ark that holds the Torah to be vertical?
• How to make a ParametricPlot3D into solid shape
• Sticker on caption phone says that using the captions can be illegal. Why?
• Group automorphism fixing finite-index subgroup
• A simplified Blackjack C++ OOP console game
• If every function is continuous if and only if its projections are continuous, can we conclude the codomain has the product topology?
• R Squared Causal Inference
• Uppercase “God” in translations of Greek plays
• How can I address my colleague communicating with us via chatGPT?
• Invalid coefficients in Quantum Process Tomography of the Hadamard gate
• Clarification on proof of the algebraic completeness of nimbers
• Difference between 頁 and ページ
• How do you hide an investigation of alien ruins on the moon during Apollo 11?
• When was this photo taken?

cppreference.com

Std::inplace_vector<t,n>:: insert_range.

Inserts, in non-reversing order, copies of elements in rg before pos .

Each iterator in the range rg is dereferenced exactly once.

rg must not overlap with the container. Otherwise, the behavior is undefined.

[ edit ] Parameters

[ edit ] Return value

An iterator that points at the copy of the first element inserted into inplace_vector or at pos if rg is empty.

• std::bad_alloc , if ranges:: distance ( rg ) + size ( ) > capacity ( ) . The elements of * this are not modified.
• Any exception thrown by insertion (i.e. by copy/move constructor, move/copy assignment operator of T ) or by any LegacyInputIterator operation. The elements of * this in the range [ ​ 0 ​ ,  pos ) are not modified.

[ edit ] Example

Possible output:

[ edit ] See also

• Recent changes
• Offline version
• What links here
• Related changes
• Upload file
• Special pages
• Printable version
• Permanent link
• Page information
• In other languages
• This page was last modified on 21 August 2024, at 07:13.
• Privacy policy
• About cppreference.com
• Disclaimers