Move assignment operator: Difference between revisions

Revision as of 11:01, 18 December 2020

Latest revision as of 14:48, 10 February 2025

(4 intermediate revisions by 3 users not shown)

Line 1:

{{Short description|Operator used in C++}}

In the [[C++|C++ programming language]], the '''move assignment operator''' <code>=</code> is used for transferring a temporary object to an existing object. The move assignment operator, like most C++ operators, can be [[Operator overloading|overloaded]]. Like the [[copy assignment operator]] it is a [[special member functions|special member function]].

If the move assignment operator is not explicitly defined, the [[compiler]] generates an implicit move assignment operator ([[C++11]] and newer) provided that [[Copy constructor (C++)|copy]]/[[C++11|move constructorsconstructor]]s, [[Assignment operator (C++)|copy assignment operator]] or [[Destructor (computer programming)|destructors]] have not been declared.<ref name=":0" /> The parameter of a move assignment operator is an [[rvalue reference]] ({{Mono|T&&}}) to type ''T'', where ''T'' is the object that defines the move assignment operator. The move assignment operator is different than a [[move constructor]] because a move assignment operator is called on an existing object, while a move constructor is called on an object created by the operation. Thereafter, the other object's data is no longer valid.

== Overloading move assignment operator ==

Line 10 ⟶ 11:

* The current object's data is de-allocated.

* The object that is being moved from must have its data marked as [[nullptr]] (or something to signify the move)

* The operator must return a reference to "{{Mono|*this}}".

Consider the following move assignment operator for a simple string class:<ref>{{Cite web|title = Move Constructors and Move Assignment Operators (C++)|url = https://msdn.microsoft.com/en-us/library/dd293665.aspx|website = msdn.microsoft.com|access-date = 2016-02-23}}</ref><syntaxhighlight lang="c++">

Line 18 ⟶ 19:

// If we're not trying to move the object into itself...

if (this != &other) {

delete[] this->data_; // DeleteFree thethis string's original data.

this->data_ = other.data_; // Copy the other string's data pointer into this string.

other.data_ = nullptr; // Finally, reset the other string's data pointer.

}

Line 32 ⟶ 33:

==References==

<references />

{{C++ programming language}}

[[Category:C++]]