cppreference assignment

[ edit ] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[ edit ] See also

Operator precedence

Operator overloading

• Todo no example
• 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 November 2022, at 04:25.
• This page has been accessed 357,612 times.
• Privacy policy
• About cppreference.com
• Disclaimers

cppreference.com

Copy assignment operator.

A copy assignment operator of class T is a non-template non-static member function with the name operator = that takes exactly one parameter of type T , T & , const T & , volatile T & , or const volatile T & . For a type to be CopyAssignable , it must have a public copy assignment operator.

[ edit ] Syntax

[ edit ] Explanation

• Typical declaration of a copy assignment operator when copy-and-swap idiom can be used.
• Typical declaration of a copy assignment operator when copy-and-swap idiom cannot be used (non-swappable type or degraded performance).
• Forcing a copy assignment operator to be generated by the compiler.
• Avoiding implicit copy assignment.

The copy assignment operator is called whenever selected by overload resolution , e.g. when an object appears on the left side of an assignment expression.

[ edit ] Implicitly-declared copy assignment operator

If no user-defined copy assignment operators are provided for a class type ( struct , class , or union ), the compiler will always declare one as an inline public member of the class. This implicitly-declared copy assignment operator has the form T & T :: operator = ( const T & ) if all of the following is true:

• each direct base B of T has a copy assignment operator whose parameters are B or const B & or const volatile B & ;
• each non-static data member M of T of class type or array of class type has a copy assignment operator whose parameters are M or const M & or const volatile M & .

Otherwise the implicitly-declared copy assignment operator is declared as T & T :: operator = ( T & ) . (Note that due to these rules, the implicitly-declared copy assignment operator cannot bind to a volatile lvalue argument.)

A class can have multiple copy assignment operators, e.g. both T & T :: operator = ( const T & ) and T & T :: operator = ( T ) . If some user-defined copy assignment operators are present, the user may still force the generation of the implicitly declared copy assignment operator with the keyword default . (since C++11)

The implicitly-declared (or defaulted on its first declaration) copy assignment operator has an exception specification as described in dynamic exception specification (until C++17) exception specification (since C++17)

Because the copy assignment operator is always declared for any class, the base class assignment operator is always hidden. If a using-declaration is used to bring in the assignment operator from the base class, and its argument type could be the same as the argument type of the implicit assignment operator of the derived class, the using-declaration is also hidden by the implicit declaration.

[ edit ] Deleted implicitly-declared copy assignment operator

A implicitly-declared copy assignment operator for class T is defined as deleted if any of the following is true:

• T has a user-declared move constructor;
• T has a user-declared move assignment operator.

Otherwise, it is defined as defaulted.

A defaulted copy assignment operator for class T is defined as deleted if any of the following is true:

• T has a non-static data member of non-class type (or array thereof) that is const ;
• T has a non-static data member of a reference type;
• T has a non-static data member or a direct or virtual base class that cannot be copy-assigned (overload resolution for the copy assignment fails, or selects a deleted or inaccessible function);
• T is a union-like class , and has a variant member whose corresponding assignment operator is non-trivial.

[ edit ] Trivial copy assignment operator

The copy assignment operator for class T is trivial if all of the following is true:

• it is not user-provided (meaning, it is implicitly-defined or defaulted) , , and if it is defaulted, its signature is the same as implicitly-defined (until C++14) ;
• T has no virtual member functions;
• T has no virtual base classes;
• the copy assignment operator selected for every direct base of T is trivial;
• the copy assignment operator selected for every non-static class type (or array of class type) member of T is trivial;

A trivial copy assignment operator makes a copy of the object representation as if by std::memmove . All data types compatible with the C language (POD types) are trivially copy-assignable.

[ edit ] Implicitly-defined copy assignment operator

If the implicitly-declared copy assignment operator is neither deleted nor trivial, it is defined (that is, a function body is generated and compiled) by the compiler if odr-used . For union types, the implicitly-defined copy assignment copies the object representation (as by std::memmove ). For non-union class types ( class and struct ), the operator performs member-wise copy assignment of the object's bases and non-static members, in their initialization order, using built-in assignment for the scalars and copy assignment operator for class types.

The generation of the implicitly-defined copy assignment operator is deprecated (since C++11) if T has a user-declared destructor or user-declared copy constructor.

[ edit ] Notes

If both copy and move assignment operators are provided, overload resolution selects the move assignment if the argument is an rvalue (either a prvalue such as a nameless temporary or an xvalue such as the result of std::move ), and selects the copy assignment if the argument is an lvalue (named object or a function/operator returning lvalue reference). If only the copy assignment is provided, all argument categories select it (as long as it takes its argument by value or as reference to const, since rvalues can bind to const references), which makes copy assignment the fallback for move assignment, when move is unavailable.

It is unspecified whether virtual base class subobjects that are accessible through more than one path in the inheritance lattice, are assigned more than once by the implicitly-defined copy assignment operator (same applies to move assignment ).

See assignment operator overloading for additional detail on the expected behavior of a user-defined copy-assignment operator.

[ edit ] Example

[ edit ] defect reports.

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

• Pages with unreviewed CWG DR marker
• 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 9 January 2019, at 07:16.
• This page has been accessed 570,566 times.
• Privacy policy
• About cppreference.com
• Disclaimers

cppreference.com

Assignment operators

Assignment operators modify the value of the object.

[ edit ] Explanation

basic assignment operator replaces the contents of the object a with those of b

move assignment operator replaces the contents of the object a with those of b while minimizing copying overhead (no deep copy is performed). It complements the basic assignment operator. (since C++11)

Other assignment operators modify the contents of the object. Usually they are overloaded in classes performing mathematical operations.

[ edit ] See also

Operator precedence

• Recent changes
• Offline version
• What links here
• Related changes
• Upload file
• Special pages
• Printable version
• Permanent link
• This page was last modified on 15 June 2012, at 14:14.
• This page has been accessed 1,039 times.
• Privacy policy
• About cppreference.com
• Disclaimers

Copy assignment operator

A copy assignment operator of class T is a non-template non-static member function with the name operator = that takes exactly one parameter of type T , T & , const T & , volatile T & , or const volatile T & . A type with a public copy assignment operator is CopyAssignable .

[ edit ] Syntax

[ edit ] Explanation

• Typical declaration of a copy assignment operator when copy-and-swap idiom can be used
• Typical declaration of a copy assignment operator when copy-and-swap idiom cannot be used
• Forcing a copy assignment operator to be generated by the compiler
• Avoiding implicit copy assignment

The copy assignment operator is called whenever selected by overload resolution , e.g. when an object appears on the left side of an assignment expression.

[ edit ] Implicitly-declared copy assignment operator

If no user-defined copy assignment operators are provided for a class type ( struct , class , or union ), the compiler will always declare one as an inline public member of the class. This implicitly-declared copy assignment operator has the form T & T :: operator = ( const T & ) if all of the following is true:

• each direct base B of T has a copy assignment operator whose parameters are B or const B& or const volatile B &
• each non-static data member M of T of class type or array of class type has a copy assignment operator whose parameters are M or const M& or const volatile M &

Otherwise the implicitly-declared copy assignment operator is declared as T & T :: operator = ( T & ) . (Note that due to these rules, the implicitly-declared copy assignment operator cannot bind to a volatile lvalue argument)

A class can have multiple copy assignment operators, e.g. both T & T :: operator = ( const T & ) and T & T :: operator = ( T ) . If some user-defined copy assignment operators are present, the user may still force the generation of the implicitly declared copy assignment operator with the keyword default .

Because the copy assignment operator is always declared for any class, the base class assignment operator is always hidden. If a using-declaration is used to bring in the assignment operator from the base class, and its argument type could be the same as the argument type of the implicit assignment operator of the derived class, the using-declaration is also hidden by the implicit declaration.

[ edit ] Deleted implicitly-declared copy assignment operator

The implicitly-declared or defaulted copy assignment operator for class T is defined as deleted in any of the following is true:

• T has a non-static data member that is const
• T has a non-static data member of a reference type.
• T has a non-static data member that cannot be copy-assigned (has deleted, inaccessible, or ambiguous copy assignment operator)
• T has direct or virtual base class that cannot be copy-assigned (has deleted, inaccessible, or ambiguous move assignment operator)
• T has a user-declared move constructor
• T has a user-declared move assignment operator

[ edit ] Trivial copy assignment operator

The implicitly-declared copy assignment operator for class T is trivial if all of the following is true:

• T has no virtual member functions
• T has no virtual base classes
• The copy assignment operator selected for every direct base of T is trivial
• The copy assignment operator selected for every non-static class type (or array of class type) memeber of T is trivial

A trivial copy assignment operator makes a copy of the object representation as if by std:: memmove . All data types compatible with the C language (POD types) are trivially copy-assignable.

[ edit ] Implicitly-defined copy assignment operator

If the implicitly-declared copy assignment operator is not deleted or trivial, it is defined (that is, a function body is generated and compiled) by the compiler. For union types, the implicitly-defined copy assignment copies the object representation (as by std:: memmove ). For non-union class types ( class and struct ), the operator performs member-wise copy assignment of the object's bases and non-static members, in their initialization order, using, using built-in assignment for the scalars and copy assignment operator for class types.

The generation of the implicitly-defined copy assignment operator is deprecated (since C++11) if T has a user-declared destructor or user-declared copy constructor.

[ edit ] Notes

If both copy and move assignment operators are provided, overload resolution selects the move assignment if the argument is an rvalue (either prvalue such as a nameless temporary or xvalue such as the result of std:: move ), and selects the copy assignment if the argument is lvalue (named object or a function/operator returning lvalue reference). If only the copy assignment is provided, all argument categories select it (as long as it takes its argument by value or as reference to const, since rvalues can bind to const references), which makes copy assignment the fallback for move assignment, when move is unavailable.

[ edit ] Copy and swap

Copy assignment operator can be expressed in terms of copy constructor, destructor, and the swap() member function, if one is provided:

T & T :: operator = ( T arg ) { // copy/move constructor is called to construct arg     swap ( arg ) ;     // resources exchanged between *this and arg     return * this ; }   // destructor is called to release the resources formerly held by *this

For non-throwing swap(), this form provides strong exception guarantee . For rvalue arguments, this form automatically invokes the move constructor, and is sometimes referred to as "unifying assignment operator" (as in, both copy and move).

[ edit ] Example

cppreference.com

Assignment operators

Assignment operators modify the value of the object.

[ edit ] Explanation

copy assignment operator replaces the contents of the object a with a copy of the contents of b ( b is not modified). For class types, this is a special member function, described in copy assignment operator .

move assignment operator replaces the contents of the object a with the contents of b , avoiding copying if possible ( b may be modified). For class types, this is a special member function, described in move assignment operator . (since C++11)

For non-class types, copy and move assignment are indistinguishable and are referred to as direct assignment .

compound assignment operators replace the contents of the object a with the result of a binary operation between the previous value of a and the value of b .

[ edit ] Builtin direct assignment

For every type T , the following function signatures participate in overload resolution:

For every enumeration or pointer to member type T , optionally volatile-qualified, the following function signature participates in overload resolution:

For every pair A1 and A2, where A1 is an arithmetic type (optionally volatile-qualified) and A2 is a promoted arithmetic type, the following function signature participates in overload resolution:

For expressions E1 of any scalar type T , the following additional forms of the builtin assignment expression are allowed:

Note: the above includes all non-class types except reference types, array types, function types, and the type void , which are not directly assignable.

The direct assignment operator expects a modifiable lvalue as its left operand and an rvalue expression or a braced-init-list (since C++11) as its right operand, and returns an lvalue identifying the left operand after modification.

For non-class types, the right operand is first implicitly converted to the cv-unqualified type of the left operand, and then its value is copied into the object identified by left operand.

When the left operand has reference type, the assignment operator modifies the referred-to object.

If the left and the right operands identify overlapping objects, the behavior is undefined (unless the overlap is exact and the type is the same)

[ edit ] Example

[ edit ] builtin compound assignment.

For every pair A1 and A2, where A1 is an arithmetic type (optionally volatile-qualified) and A2 is a promoted arithmetic type, the following function signatures participate in overload resolution:

For every pair I1 and I2, where I1 is an integral type (optionally volatile-qualified) and I2 is a promoted integral type, the following function signatures participate in overload resolution:

For every optionally cv-qualified object type T , the following function signatures participate in overload resolution:

The behavior of every builtin compound-assignment expression E1 op = E2 (where E1 is a modifiable lvalue expression and E2 is an rvalue expression or a braced-init-list (since C++11) ) is exactly the same as the behavior of the expression E1 = E1 op E2 , except that the expression E1 is evaluated only once and that it behaves as a single operation with respect to indeterminately-sequenced function calls (e.g. in f ( a + = b, g ( ) ) , the += is either not started at all or is completed as seen from inside g ( ) ).

This section is incomplete
Reason: no example

[ edit ] See also

Operator precedence

Operator overloading

Common operators
a = b a += b a -= b a *= b a /= b a %= b a &= b a |= b a ^= b a <<= b a >>= b	++a --a a++ a--	+a -a a + b a - b a * b a / b a % b ~a a & b a | b a ^ b a << b a >> b	!a a && b a || b	a == b a != b a < b a > b a <= b a >= b	a[b] *a &a a->b a.b a->*b a.*b	a(...) a, b ? :
Special operators
converts one type to another related type converts within inheritance hierarchies adds or removes qualifiers converts type to unrelated type converts one type to another by a mix of , , and allocates memory deallocates memory queries the size of a type queries the size of a (since C++11) queries the type information of a type checks if an expression can throw an exception (since C++11) queries alignment requirements of a type (since C++11)

• Todo no example
• 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 11 March 2015, at 23:51.
• This page has been accessed 32,825 times.
• Privacy policy
• About cppreference.com
• Disclaimers

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.

Copy constructors and copy assignment operators (C++)

• 8 contributors

Starting in C++11, two kinds of assignment are supported in the language: copy assignment and move assignment . In this article "assignment" means copy assignment unless explicitly stated otherwise. For information about move assignment, see Move Constructors and Move Assignment Operators (C++) .

Both the assignment operation and the initialization operation cause objects to be copied.

Assignment : When one object's value is assigned to another object, the first object is copied to the second object. So, this code copies the value of b into a :

Initialization : Initialization occurs when you declare a new object, when you pass function arguments by value, or when you return by value from a function.

You can define the semantics of "copy" for objects of class type. For example, consider this code:

The preceding code could mean "copy the contents of FILE1.DAT to FILE2.DAT" or it could mean "ignore FILE2.DAT and make b a second handle to FILE1.DAT." You must attach appropriate copying semantics to each class, as follows:

Use an assignment operator operator= that returns a reference to the class type and takes one parameter that's passed by const reference—for example ClassName& operator=(const ClassName& x); .

Use the copy constructor.

If you don't declare a copy constructor, the compiler generates a member-wise copy constructor for you. Similarly, if you don't declare a copy assignment operator, the compiler generates a member-wise copy assignment operator for you. Declaring a copy constructor doesn't suppress the compiler-generated copy assignment operator, and vice-versa. If you implement either one, we recommend that you implement the other one, too. When you implement both, the meaning of the code is clear.

The copy constructor takes an argument of type ClassName& , where ClassName is the name of the class. For example:

Make the type of the copy constructor's argument const ClassName& whenever possible. This prevents the copy constructor from accidentally changing the copied object. It also lets you copy from const objects.

Compiler generated copy constructors

Compiler-generated copy constructors, like user-defined copy constructors, have a single argument of type "reference to class-name ." An exception is when all base classes and member classes have copy constructors declared as taking a single argument of type const class-name & . In such a case, the compiler-generated copy constructor's argument is also const .

When the argument type to the copy constructor isn't const , initialization by copying a const object generates an error. The reverse isn't true: If the argument is const , you can initialize by copying an object that's not const .

Compiler-generated assignment operators follow the same pattern for const . They take a single argument of type ClassName& unless the assignment operators in all base and member classes take arguments of type const ClassName& . In this case, the generated assignment operator for the class takes a const argument.

When virtual base classes are initialized by copy constructors, whether compiler-generated or user-defined, they're initialized only once: at the point when they are constructed.

The implications are similar to the copy constructor. When the argument type isn't const , assignment from a const object generates an error. The reverse isn't true: If a const value is assigned to a value that's not const , the assignment succeeds.

For more information about overloaded assignment operators, see Assignment .

Was this page helpful?

Additional resources

• 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.

Move-assignment and reference member

Copy-assignment for a class with a reference member variable is a no-no because you can't reassign the reference. But what about move-assignment? I tried simply move ing it but, of course, that destroys the source object when I just want to move the reference itself:

Should I just not be implementing move-assignment and sticking with move-construction only? That makes swap(C&, C&) hard to implement.

• move-semantics

• 3 In general if one wants to do non-trivial stuff with references, wouldn't one be using reference_wrapper<T> and be done with it? I'm sure that would make move constructor and assignment near-trivial, if not trivial (note not trivial ). –  Luis Machuca Commented Dec 10, 2013 at 1:42
• @LuisMachuca That seems to work. If you add it as an answer, I'll upvote it. Thanks. –  thehouse Commented Dec 10, 2013 at 2:06
• You're sort of missing a declaration for x_ ... –  ildjarn Commented Dec 10, 2013 at 8:49
• @ildjarn Whoops! Fixed now. Thanks. –  thehouse Commented Dec 10, 2013 at 10:28
• I was a bit confused by this question, so for reference: you talk about "move assignment", but the c2 = c1 line is not a move assignment, it is a copy assignment (and thus the reference member is a problem). It should be c2 = std::move(c1) , perhaps. You actually can make this work, but the problem is that there's no way to mark the state as being 'invalid' in the moved-from objects. See this example: godbolt.org/z/en4aP8 –  jwd Commented Mar 20, 2021 at 18:40

2 Answers 2

(Posted as an answer from comment as suggested by the OP)

In general if one wants to do non-trivial stuff with references in C++, one would be using reference_wrapper<T> , which is essentially a fancy value-semantic stand-in for a T& , then one would be done with it - it already provides (re)assignment and other operations. I'm sure that would make move constructor and assignment near-trivial, if not trivial (note not trivial as in per the is_trivially_* semantics).

"Reference wrapper" is added to C++03 as part of TR1, and is part of C++11.

Documentation: http://en.cppreference.com/w/cpp/utility/functional/reference_wrapper

• 1 It is worth promoting comments to answers just so we have more visible up/down voting buttons –  sage Commented Jun 16, 2018 at 0:31
• 3 reference_wrapper is not movable, so this does not really solve the problem. As far as I can tell, if you want your class to contain a reference and be movable, you have to use a pointer. –  Nemo Commented Nov 8, 2019 at 18:47
• 1 @Nemo A class that contains an std::reference_wrapper can also have a copy constructor by rvalue / assignment operator by rvalue, so doesn't that serve to answer the original question? In the above case it would allow you to use all the defaults, using the Rule of Zero. –  Elliott Commented Dec 6, 2019 at 16:27

A reference is, in some sense, a T *const with syntactic sugar on top to auto-derefence, auto-capture, and auto-lifetime extend temporaries. (note that this is not quite true, but often is in practice and practicality)

If you want a reseatable reference, C++ has those: they are called pointers. You can use an accessor to replace dereferencing with a function call if you like. The remaining feature (temporary lifetime extension) that is hard to emulate does not apply to struct members.

• 4 Pointers have weaker semantics than just reseatable references. For example, you can assign NULL to them. More importantly, they don't document the intent at all (write-code-to-be-read-not-executed etc.). –  thehouse Commented Dec 10, 2013 at 17:47

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++ c++11 move-semantics or ask your own question .

• The Overflow Blog
• Where developers feel AI coding tools are working—and where they’re missing...
• He sold his first company for billions. Now he’s building a better developer...
• Featured on Meta
• User activation: Learnings and opportunities
• Preventing unauthorized automated access to the network
• Announcing the new Staging Ground Reviewer Stats Widget

Hot Network Questions

• How to apply a function to specific rows of a matrix
• What is the equivalent of mechanical AND gate?
• Making sense of NAND latch circuit diagram
• Want a different order than permutation
• US Law Questions & Gray Flannel Suit Man
• I need a temporary hoist and track system to lift a dead chest freezer up through a tight stairwell
• Mustard type paste in my radiator
• Could you suffocate someone to death with a big enough standing wave?
• Expected value of a matrix = matrix of expected value?
• Graphic to fit in Cell Tabularray
• Bridge in a walled garden
• \usepackage[<language>]{babel} or \babelprovide{<language>}? Why?
• If a professor wants to hire a student themselves, how can they write a letter of recommendation for other universities?
• Why doesn't SpaceX use a normal blast trench like Saturn V?
• Is a private third party allowed to take things to court?
• Why aren't some "conditions" officially a condition? (Burning, Bloodied)
• Enhancing my RSA implement in Python
• How to align view to uneven face to get straight orientation? (without the need of rolling/rotating view afterwards)
• Object origin axes not perpendicular to its surface
• U.S Citizen married to Danish Citizen living in Sweden with active resident card application - Can we travel to Denmark together?
• Can we divide the story points across team members?
• Are there individual protons and neutrons in a nucleus?
• Folding a 70º coffee filter cone
• How can I grep to include the surrounding lines?

Learn C++ practically and Get Certified .

Popular Tutorials

Popular examples, reference materials, learn c++ interactively, introduction to c++.

• Getting Started With C++
• Your First C++ Program
• C++ Comments

C++ Fundamentals

• C++ Keywords and Identifiers
• C++ Variables, Literals and Constants
• C++ Data Types
• C++ Type Modifiers
• C++ Constants
• C++ Basic Input/Output

C++ Operators

Flow Control

C++ Relational and Logical Operators

• C++ if, if...else and Nested if...else
• C++ for Loop
• C++ while and do...while Loop
• C++ break Statement
• C++ continue Statement
• C++ goto Statement
• C++ switch..case Statement
• C++ Ternary Operator
• C++ Functions
• C++ Programming Default Arguments
• C++ Function Overloading
• C++ Inline Functions
• C++ Recursion

Arrays and Strings

• C++ Array to Function
• C++ Multidimensional Arrays
• C++ String Class

Pointers and References

• C++ Pointers
• C++ Pointers and Arrays
• C++ References: Using Pointers
• C++ Call by Reference: Using pointers
• C++ Memory Management: new and delete

Structures and Enumerations

• C++ Structures
• C++ Structure and Function

C++ Pointers to Structure

• C++ Enumeration

Object Oriented Programming

• C++ Classes and Objects
• C++ Constructors
• C++ Constructor Overloading
• C++ Destructors
• C++ Access Modifiers
• C++ Encapsulation
• C++ friend Function and friend Classes

Inheritance & Polymorphism

• C++ Inheritance
• C++ Public, Protected and Private Inheritance
• C++ Multiple, Multilevel and Hierarchical Inheritance
• C++ Function Overriding
• C++ Virtual Functions
• C++ Abstract Class and Pure Virtual Function

STL - Vector, Queue & Stack

• C++ Standard Template Library
• C++ STL Containers
• C++ std::array
• C++ Vectors
• C++ Forward List
• C++ Priority Queue

STL - Map & Set

• C++ Multimap
• C++ Multiset
• C++ Unordered Map
• C++ Unordered Set
• C++ Unordered Multiset
• C++ Unordered Multimap

STL - Iterators & Algorithms

• C++ Iterators
• C++ Algorithm
• C++ Functor

Additional Topics

• C++ Exceptions Handling
• C++ File Handling
• C++ Ranged for Loop
• C++ Nested Loop
• C++ Function Template
• C++ Class Templates
• C++ Type Conversion
• C++ Type Conversion Operators
• C++ Operator Overloading

Advanced Topics

• C++ Namespaces
• C++ Preprocessors and Macros
• C++ Storage Class

C++ Bitwise Operators

• C++ Buffers
• C++ istream
• C++ ostream

C++ Tutorials

C++ operator precedence and associativity.

• C++ Operators Precedence

If there are multiple operators in a single expression, the operations are not evaluated simultaneously. Rather, operators with higher precedence have their operations evaluated first.

Let us consider an example:

Here, the multiplication operator * is of higher level precedence than the subtraction operator - . Hence, 17 * 6 is evaluated first.

As a result, the above expression is equivalent to

If we wish to evaluate 5 - 17 first, then we must enclose them within parentheses :

Example 1: Operators Precedence

Note: Because there are a lot of operators in C++ with multiple levels of precedence, it is highly recommended that we use parentheses to make our code more readable.

C++ Operators Precedence Table

The following table (taken from cppreference.com ) shows the precedence of C++ operators. Precedence Level 1 signifies operators of highest priority, while Precedence Level 17 signifies operators of the lowest priority.

The property of associativity will be discussed shortly.

Precedence	Operator	Description	Associativity
1	::	Scope Resolution	Left to Right
2	a++ a-- type( ) type{ } a( ) a[ ] . ->	Suffix/postfix increment Suffix/postfix decrement Function cast Function cast Function call Subscript Member access from an object Member access from object ptr	Left to Right
3	++a --a +a -a ! ~ (type) *a &a sizeof co_await new new[ ] delete delete[]	Prefix increment Prefix decrement Unary plus Unary minus Logical NOT Bitwise NOT C style cast Indirection (dereference) Address-of Size-of await-expression Dynamic memory allocation Dynamic memory deallocation	Right to Left
4	.* ->*	Member object selector Member pointer selector	Left to Right
5	a * b a / b a % b	Multiplication Division Modulus	Left to Right
6	a + b a - b	Addition Subtraction	Left to Right
7	<< >>	Bitwise left shift Bitwise right shift	Left to Right
8	<=>	Three-way comparison operator	Left to Right
9	< <= > >=	Less than Less than or equal to Greater than Greater than or equal to	Left to Right
10	== !=	Equal to Not equal to	Left to Right
11	&	Bitwise AND	Left to Right
12	^	Bitwise XOR	Left to Right
13	|	Bitwise OR	Left to Right
14	&&	Logical AND	Left to Right
15	||	Logical OR	Left to Right
16	a ? b : c throw co_yield = += -= *= /= %= <<= >>= &= ^= |=	Ternary Conditional throw operator yield expression (C++ 20) Assignment Addition Assignment Subtraction Assignment Multiplication Assignment Division Assignment Modulus Assignment Bitwise Shift Left Assignment Bitwise Shift Right Assignment Bitwise AND Assignment Bitwise XOR Assignment Bitwise OR Assignment	Right to Left
17	,	Comma operator	Left to Right

• C++ Operators Associativity

Operator associativity is the direction from which an expression is evaluated. For example,

Take a look at a = 4; statement. The associativity of the = operator is from right to left. Hence, the value of b is assigned to a , and not in the other direction.

Also, multiple operators can have the same level of precedence (as we can see from the above table). When multiple operators of the same precedence level are used in an expression, they are evaluated according to their associativity .

Both operators += and -= operators have the same precedence. Since the associativity of these operators is from right to left, here is how the last statement is evaluated.

• a -= 6 is evaluated first. Hence, a will be -5
• Then, b += -5 will be evaluated. Hence, b will be -1

Example 2: Operators Associativity

Table of contents.

• Example: Operators Precedence
• C++ Operators Precedence List
• Example: Operators Associativity

Sorry about that.

Our premium learning platform, created with over a decade of experience and thousands of feedbacks .

Learn and improve your coding skills like never before.

• Interactive Courses
• Certificates
• 2000+ Challenges

Related Tutorials

C++ Tutorial