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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.


class_name class_name ( class_name )	(1)

class_name class_name ( const class_name )	(2)

class_name class_name ( const class_name ) = default;	(3)	(since C++11)

class_name class_name ( const class_name ) = delete;	(4)	(since C++11)

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.

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.

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.

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;

has no non-static data members of -qualified type.

(since C++14)

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.

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.

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.

Defect reports

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

DR	Applied to	Behavior as published	Correct behavior
	C++14	operator=(X&) = default was non-trivial	made trivial

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Copy constructors, assignment operators,

Copy constructors, assignment operators, and exception safe assignment

MyClass& other ); MyClass( MyClass& other ); MyClass( MyClass& other ); MyClass( MyClass& other );

MyClass* other );

MyClass { x; c; std::string s; };

MyClass& other ) : x( other.x ), c( other.c ), s( other.s ) {}

);

print_me_bad( std::string& s ) { std::cout << s << std::endl; } print_me_good( std::string& s ) { std::cout << s << std::endl; } std::string hello( ); print_me_bad( hello ); print_me_bad( std::string( ) ); print_me_bad( ); print_me_good( hello ); print_me_good( std::string( ) ); print_me_good( );

, );

=( MyClass& other ) { x = other.x; c = other.c; s = other.s; * ; }

< T > MyArray { size_t numElements; T* pElements; : size_t count() { numElements; } MyArray& =( MyArray& rhs ); };

<> MyArray<T>:: =( MyArray& rhs ) { ( != &rhs ) { [] pElements; pElements = T[ rhs.numElements ]; ( size_t i = 0; i < rhs.numElements; ++i ) pElements[ i ] = rhs.pElements[ i ]; numElements = rhs.numElements; } * ; }

<> MyArray<T>:: =( MyArray& rhs ) { MyArray tmp( rhs ); std::swap( numElements, tmp.numElements ); std::swap( pElements, tmp.pElements ); * ; }

< T > swap( T& one, T& two ) { T tmp( one ); one = two; two = tmp; }

<> MyArray<T>:: =( MyArray tmp ) { std::swap( numElements, tmp.numElements ); std::swap( pElements, tmp.pElements ); * ; }

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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 .

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When should we write our own assignment operator in C++?

The answer is same as Copy Constructor. If a class doesn’t contain pointers, then there is no need to write assignment operator and copy constructor. The compiler creates a default copy constructor and assignment operators for every class. The compiler created copy constructor and assignment operator may not be sufficient when we have pointers or any run time allocation of resource like file handle, a network connection..etc. For example, consider the following program.

Output of above program is “10”. If we take a look at main(), we modified ‘t1’ using setValue() function, but the changes are also reflected in object ‘t2’. This type of unexpected changes cause problems. Since there is no user defined assignment operator in the above program, compiler creates a default assignment operator, which copies ‘ptr’ of right hand side to left hand side. So both ‘ptr’s start pointing to the same location.

We can handle the above problem in two ways.

1) Do not allow assignment of one object to other object. We can create our own dummy assignment operator and make it private.

2) Write your own assignment operator that does deep copy.

Same is true for Copy Constructor.

Following is an example of overloading assignment operator for the above class.

We should also add a copy constructor to the above class, so that the statements like “Test t3 = t4;” also don’t cause any problem.

Note the if condition in assignment operator. While overloading assignment operator, we must check for self assignment. Otherwise assigning an object to itself may lead to unexpected results (See this ). Self assignment check is not necessary for the above ‘Test’ class, because ‘ptr’ always points to one integer and we may reuse the same memory. But in general, it is a recommended practice to do self-assignment check.

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Syntax Explanation Implicitly-declared copy assignment operator Deleted implicitly-declared copy assignment operator Trivial copy assignment operator Eligible copy assignment operator Implicitly-defined copy assignment operator Notes Example Defect reports See also

[ edit ] Syntax


class-name class-name class-name	(1)

class-name class-name const class-name	(2)

class-name class-name const class-name	(3)	(since C++11)

class-name class-name const class-name	(4)	(since C++11)

[ edit ] Explanation

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

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 & .

A class can have multiple copy assignment operators, e.g. both T & T :: operator = ( 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)

[ edit ] Deleted implicitly-declared copy assignment operator

An 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 a const-qualified non-class type (or array thereof);
T has a non-static data member of a reference type;
T has a non-static data member or a direct 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);
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 ] Eligible copy assignment operator

A copy assignment operator is eligible if it is either user-declared or both implicitly-declared and definable.	(until C++11)
A copy assignment operator is eligible if it is not deleted.	(since C++11) (until C++20)
A copy assignment operator is eligible if , if any, are satisfied, and than it.	(since C++20)

Triviality of eligible copy assignment operators determines whether the class is a trivially copyable type .

[ 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 or needed for constant evaluation (since C++14) . 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 implicitly-defined copy assignment operator for a class is if is a , and that is of class type (or array thereof), the assignment operator selected to copy that member is a constexpr function.	(since C++14) (until C++23)
The implicitly-defined copy assignment operator for a class is .	(since C++23)

The generation of the implicitly-defined copy assignment operator is deprecated if has a user-declared destructor or user-declared copy constructor.

(since C++11)

[ edit ] Notes

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.

Applied to	Behavior as published	Correct behavior
C++11	a volatile subobject made defaulted copy assignment operators non-trivial ( )	triviality not affected
C++11	operator=(X&) = default was non-trivial	made trivial
C++11	a defaulted copy assignment operator for class was not defined as deleted if is abstract and has non-copy-assignable direct virtual base classes	the operator is defined as deleted in this case

[ edit ] See also

converting constructor
copy constructor
copy elision
default constructor
aggregate initialization
constant initialization
copy initialization
default initialization
direct initialization
initializer list
list initialization
reference initialization
value initialization
zero initialization
move assignment
move constructor
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Customizes the C++ operators for operands of user-defined types.

Overloaded operators are functions with special function names:


op	(1)

type	(2)

	(3)

	(4)

suffix-identifier	(5)	(since C++11)

any of the following 38 (until C++20)40 (since C++20) operators:+ - * / % ^ & | ~ ! = < > += -= *= /= %= ^= &= |= << >> >>= <<= == != <= >= <=> (since C++20) && || ++ -- , ->* -> ( ) [ ] co_await (since C++20)

Overloaded operators

When an operator appears in an expression , and at least one of its operands has a class type or an enumeration type , then overload resolution is used to determine the user-defined function to be called among all the functions whose signatures match the following:

Expression	As member function	As non-member function	Example
@a	(a).operator@ ( )	operator@ (a)	! calls .operator!()
a@b	(a).operator@ (b)	operator@ (a, b)	<< 42 calls .operator<<(42)
a=b	(a).operator= (b)	cannot be non-member	s; s = "abc"; calls s.operator=("abc")
a(b...)	(a).operator()(b...)	cannot be non-member	r; auto n = r(); calls r.operator()()
a[b]	(a).operator[](b)	cannot be non-member	<int, int> m; m[1] = 2; calls m.operator[](1)
a->	(a).operator-> ( )	cannot be non-member	auto p = <S>(); p->bar() calls p.operator->()
a@	(a).operator@ (0)	operator@ (a, 0)	<int>::iterator i = v.begin(); i++ calls i.operator++(0)
in this table, is a placeholder representing all matching operators: all prefix operators in @a, all postfix operators other than -> in a@, all infix operators other than = in a@b

Note: for overloading user-defined conversion functions , user-defined literals , allocation and deallocation see their respective articles.

Overloaded operators (but not the built-in operators) can be called using function notation:

Restrictions

The operators :: (scope resolution), . (member access), .* (member access through pointer to member), and ?: (ternary conditional) cannot be overloaded.
New operators such as ** , <> , or &| cannot be created.
The overloads of operators && and || lose short-circuit evaluation.
The overload of operator -> must either return a raw pointer, or return an object (by reference or by value) for which operator -> is in turn overloaded.
It is not possible to change the precedence, grouping, or number of operands of operators.

, , and (comma) lose their special when overloaded and behave like regular function calls even when they are used without function-call notation.

(until C++17)

Canonical implementations

Other than the restrictions above, the language puts no other constraints on what the overloaded operators do, or on the return type (it does not participate in overload resolution), but in general, overloaded operators are expected to behave as similar as possible to the built-in operators: operator + is expected to add, rather than multiply its arguments, operator = is expected to assign, etc. The related operators are expected to behave similarly ( operator + and operator + = do the same addition-like operation). The return types are limited by the expressions in which the operator is expected to be used: for example, assignment operators return by reference to make it possible to write a = b = c = d , because the built-in operators allow that.

Commonly overloaded operators have the following typical, canonical forms: [1]

Assignment operator

The assignment operator ( operator = ) has special properties: see copy assignment and move assignment for details.

The canonical copy-assignment operator is expected to perform no action on self-assignment , and to return the lhs by reference:

The canonical move assignment is expected to leave the moved-from object in valid state (that is, a state with class invariants intact), and either do nothing or at least leave the object in a valid state on self-assignment, and return the lhs by reference to non-const, and be noexcept:

In those situations where copy assignment cannot benefit from resource reuse (it does not manage a heap-allocated array and does not have a (possibly transitive) member that does, such as a member std::vector or std::string ), there is a popular convenient shorthand: the copy-and-swap assignment operator, which takes its parameter by value (thus working as both copy- and move-assignment depending on the value category of the argument), swaps with the parameter, and lets the destructor clean it up.

This form automatically provides strong exception guarantee , but prohibits resource reuse.

Stream extraction and insertion

The overloads of operator>> and operator<< that take a std:: istream & or std:: ostream & as the left hand argument are known as insertion and extraction operators. Since they take the user-defined type as the right argument ( b in a@b ), they must be implemented as non-members.

These operators are sometimes implemented as friend functions .

Function call operator

When a user-defined class overloads the function call operator, operator ( ) , it becomes a FunctionObject type. Many standard algorithms, from std:: sort to std:: accumulate accept objects of such types to customize behavior. There are no particularly notable canonical forms of operator ( ) , but to illustrate the usage

Increment and decrement

When the postfix increment and decrement appear in an expression, the corresponding user-defined function ( operator ++ or operator -- ) is called with an integer argument 0 . Typically, it is implemented as T operator ++ ( int ) , where the argument is ignored. The postfix increment and decrement operator is usually implemented in terms of the prefix version:

Although canonical form of pre-increment/pre-decrement returns a reference, as with any operator overload, the return type is user-defined; for example the overloads of these operators for std::atomic return by value.

Binary arithmetic operators

Binary operators are typically implemented as non-members to maintain symmetry (for example, when adding a complex number and an integer, if operator+ is a member function of the complex type, then only complex + integer would compile, and not integer + complex ). Since for every binary arithmetic operator there exists a corresponding compound assignment operator, canonical forms of binary operators are implemented in terms of their compound assignments:

Relational operators

Standard algorithms such as std:: sort and containers such as std:: set expect operator < to be defined, by default, for the user-provided types, and expect it to implement strict weak ordering (thus satisfying the Compare requirements). An idiomatic way to implement strict weak ordering for a structure is to use lexicographical comparison provided by std::tie :

Typically, once operator < is provided, the other relational operators are implemented in terms of operator < .

Likewise, the inequality operator is typically implemented in terms of operator == :

When three-way comparison (such as std::memcmp or std::string::compare ) is provided, all six relational operators may be expressed through that:

All six relational operators are automatically generated by the compiler if the three-way comparison operator operator<=> is defined, and that operator, in turn, is generated by the compiler if it is defined as defaulted:

Record { name; unsigned int floor; double weight; auto operator<=>(const Record&) = default; }; // records can now be compared with ==, !=, <, <=, >, and >=

See for details.

(since C++20)

Array subscript operator

User-defined classes that provide array-like access that allows both reading and writing typically define two overloads for operator [ ] : const and non-const variants:

If the value type is known to be a built-in type, the const variant should return by value.

Where direct access to the elements of the container is not wanted or not possible or distinguishing between lvalue c [ i ] = v ; and rvalue v = c [ i ] ; usage, operator[] may return a proxy. see for example std::bitset::operator[] .

To provide multidimensional array access semantics, e.g. to implement a 3D array access a [ i ] [ j ] [ k ] = x ; , operator[] has to return a reference to a 2D plane, which has to have its own operator[] which returns a reference to a 1D row, which has to have operator[] which returns a reference to the element. To avoid this complexity, some libraries opt for overloading operator ( ) instead, so that 3D access expressions have the Fortran-like syntax a ( i, j, k ) = x ;

Bitwise arithmetic operators

User-defined classes and enumerations that implement the requirements of BitmaskType are required to overload the bitwise arithmetic operators operator & , operator | , operator ^ , operator~ , operator & = , operator | = , and operator ^ = , and may optionally overload the shift operators operator << operator >> , operator >>= , and operator <<= . The canonical implementations usually follow the pattern for binary arithmetic operators described above.

Boolean negation operator

The operator operator ! is commonly overloaded by the user-defined classes that are intended to be used in boolean contexts. Such classes also provide a user-defined conversion function explicit operator bool ( ) (see std::basic_ios for the standard library example), and the expected behavior of operator ! is to return the value opposite of operator bool .

Rarely overloaded operators

The following operators are rarely overloaded:

The address-of operator, operator & . If the unary & is applied to an lvalue of incomplete type and the complete type declares an overloaded operator & , the behavior is undefined (until C++11) it is unspecified whether the operator has the built-in meaning or the operator function is called (since C++11) . Because this operator may be overloaded, generic libraries use std::addressof to obtain addresses of objects of user-defined types. The best known example of a canonical overloaded operator& is the Microsoft class CComPtr . An example of its use in EDSL can be found in boost.spirit .
The boolean logic operators, operator && and operator || . Unlike the built-in versions, the overloads cannot implement short-circuit evaluation. Also unlike the built-in versions, they do not sequence their left operand before the right one. (until C++17) In the standard library, these operators are only overloaded for std::valarray .
The comma operator, operator, . Unlike the built-in version, the overloads do not sequence their left operand before the right one. (until C++17) Because this operator may be overloaded, generic libraries use expressions such as a, void ( ) ,b instead of a,b to sequence execution of expressions of user-defined types. The boost library uses operator, in boost.assign , boost.spirit , and other libraries. The database access library SOCI also overloads operator, .
The member access through pointer to member operator - > * . There are no specific downsides to overloading this operator, but it is rarely used in practice. It was suggested that it could be part of smart pointer interface , and in fact is used in that capacity by actors in boost.phoenix . It is more common in EDSLs such as cpp.react .

Defect reports

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

DR	Applied to	Behavior as published	Correct behavior
	C++11	taking address of incomplete type that overloads address-of was undefined behavior	the behavior is only unspecified

Operator precedence
Alternative operator syntax

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[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 creates objects with dynamic storage duration destructs objects previously created by the new expression and releases obtained memory area 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)

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How to overload copy assignment operator for const data members?

error: passing 'const string {aka const std::__cxx11::basic_string<char>}' as 'this' argument discards qualifiers [-fpermissive]

I have a class like this and need to build a copy assignment operator where the name_ must be const .

How to overcome the error?

operator-overloading

2 maybe remove the const from the name declaration const string name_ . It may be that when you try to assign station.name to it you violate your own rule of this member to be constant. – ManyQuestions Commented Mar 7, 2021 at 13:05
4 " I have a class like this and need to build a copy assignment operator where the name_ must be const " - One of those requirements has to be dropped - unless you make a copy constructor/assignment operator that copies everything but name_ . – Ted Lyngmo Commented Mar 7, 2021 at 13:08
3 From a design perspective, you don't. Having a const member means that it is not possible to assign that member after it is initialised. But the purpose of an assignment operator is generally to assign all members of the class after they have been initialised. If you must supply an operator=() for a class with a const member you must (1) justify such a broken design (2) implement the operator=() so it assigns other members, but not the const ones. – Peter Commented Mar 7, 2021 at 13:57
@TedLyngmo Presumably the copy constructor should copy name_ , since its only other choice would be to make it empty. But if the class does that, it will violate the Principle of Least Surprise. – aschepler Commented Mar 7, 2021 at 14:03
Thanks @Peter ! for the clarification. Yes I can understand I was wrong from design perspective. – suman Commented Mar 7, 2021 at 16:31

you can use the const casting like so

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COMMENTS

Copy assignment operator
Triviality of eligible copy assignment operators determines whether the class is a trivially copyable type. [] NoteIf 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 ...
21.12
21.12 — Overloading the assignment operator. Alex July 22, 2024. The copy assignment operator (operator=) is used to copy values from one object to another already existing object. As of C++11, C++ also supports "Move assignment". We discuss move assignment in lesson 22.3 -- Move constructors and move assignment .
assignment operator overloading in c++
One thing to note is that if you aren't needing a deep copy it's sometimes considered best to use the implicit copy constructor and assignment operator generated by the compiler than roll your own. ... // Operator overloading in C++ //assignment operator overloading #include<iostream> using namespace std; class Employee { private: int idNum ...
Copy Constructor vs Assignment Operator in C++
C++ compiler implicitly provides a copy constructor, if no copy constructor is defined in the class. A bitwise copy gets created, if the Assignment operator is not overloaded. Consider the following C++ program. Explanation: Here, t2 = t1; calls the assignment operator, same as t2.operator= (t1); and Test t3 = t1; calls the copy constructor ...
C++ Assignment Operator Overloading
The assignment operator,"=", is the operator used for Assignment. It copies the right value into the left value. Assignment Operators are predefined to operate only on built-in Data types. Assignment operator overloading is binary operator overloading. Overloading assignment operator in C++ copies all values of one object to another object.
operator overloading
Commonly overloaded operators have the following typical, canonical forms: Assignment operator. The assignment operator (operator =) has special properties: see copy assignment and move assignment for details. The canonical copy-assignment operator is expected to be safe on self-assignment, and to return the lhs by reference:
Copy assignment operator
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. 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 ...
Copy assignment operator
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 ...
Assignment operator (C++)
In the C++ programming language, the assignment operator, =, is the operator used for assignment. Like most other operators in C++, it can be overloaded . The copy assignment operator, often just called the "assignment operator", is a special case of assignment operator where the source (right-hand side) and destination (left-hand side) are of ...
Copy constructors, assignment operators,
remaining lines are assignment operators which can also throw. HOWEVER, if you have a type T for which the default std::swap() may result in either T's copy constructor or assignment operator throwing, you are politely required to provide a swap() overload for your type that does not throw.
Copy constructors and copy assignment operators (C++)
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.
When should we write our own assignment operator in C++?
1) Do not allow assignment of one object to other object. We can create our own dummy assignment operator and make it private. 2) Write your own assignment operator that does deep copy. Same is true for Copy Constructor. Following is an example of overloading assignment operator for the above class. #include<iostream>.
Copy assignment operator
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. [] Implicitly-declared copy assignment operatoIf 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.
21.13
Shallow copying. Because C++ does not know much about your class, the default copy constructor and default assignment operators it provides use a copying method known as a memberwise copy (also known as a shallow copy).This means that C++ copies each member of the class individually (using the assignment operator for overloaded operator=, and direct initialization for the copy constructor).
Overloading copy assignment operator in c++
walnut. 22.1k 4 28 64. If I understand your reasoning correctly, for the example that you have provided (a=b=c), it would be simplified as follows: 1) a = (b = c); // copy assignment called first time in which b is assigned with c and reference is being returned simplifying the expression to 2) a = (reference returned when operator was first ...
Overloading assignments (C++ only)
Overloading assignments (C++ only) You overload the assignment operator, operator=, with a nonstatic member function that has only one parameter. You cannot declare an overloaded assignment operator that is a nonmember function. The following example shows how you can overload the assignment operator for a particular class: struct X {. int data;
Move assignment operator
Triviality of eligible move assignment operators determines whether the class is a trivially copyable type. [] NoteIf 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 ...
operator overloading
Commonly overloaded operators have the following typical, canonical forms: Assignment operator. The assignment operator (operator =) has special properties: see copy assignment and move assignment for details. The canonical copy-assignment operator is expected to perform no action on self-assignment, and to return the lhs by reference:
c++
When a2 is initialised, a temporary copy of a1 is made and then the operator is evaluated with respect to the Base class, hence the Base overloaded copy assignment block is run, and the a1 object is returned via return *this to the reference a2.
EECS 201
layout: true <div class=bot-bar> Python </div> --- class: center, middle # Python #### `import tensorflow as tf` --- # Overview * High level scripting * What is ...
c++
4. Correct me if I'm wrong: I understand that when having a class with members that are pointers, a copy of a class object will result in that the pointers representing the same memory address. This can result in changes done to one class object to affect all copies of this object. A solution to this can be to overload the = operator.
c++
If you must supply an operator=() for a class with a const member you must (1) justify such a broken design (2) implement the operator=() so it assigns other members, but not the const ones. @TedLyngmo Presumably the copy constructor should copy name_, since its only other choice would be to make it empty. But if the class does that, it will ...