vector assignment operator c

std::vector operator=

• since C++20
• since C++17
• since C++11
• until C++11

Replaces the contents of the container with the contents of another.

(1) Copy assignment operator. Replaces the contents with a copy of the contents of other .

If std::allocator_traits<Alloc>::propagate_on_container_copy_assignment::value is true , the allocator of *this is replaced by a copy of that of other.

If the allocator of *this after assignment would compare unequal to its old value, the old allocator is used to deallocate the memory, then the new allocator is used to allocate it before copying the elements.

Otherwise, the memory owned by *this may be reused when possible.

In any case, the elements originally belong to *this may be either destroyed or replaced by element-wise copy-assignment.

(2) Move assignment operator. Replaces the contents with those of other using move semantics (i.e. the data in other is moved from other into this container).

other is in a valid but unspecified state afterwards.

If std::allocator_traits<Alloc>::propagate_on_container_move_assignment::value is true , the allocator of *this is replaced by a copy of that of other.

If it is false and the allocators of *this and other do not compare equal, *this cannot take ownership of the memory owned by other and must move-assign each element individually, allocating additional memory using its own allocator as needed.

In any case, all elements originally belong to *this are either destroyed or replaced by element-wise move-assignment.

(3) Replaces the contents with those identified by initializer list ilist .

Parameters ​

• other - another container to use as data source
• ilist - initializer list to use as data source

Return value ​

Complexity ​.

(1) Linear in the size of *this and other - O(size() + other.size(()) .

(2) Linear in the size of *this - O(size()) . If allocators do not compare equal and do not propagate, linear in the size of *this and other - O(size() + other.size()) .

(3) Linear in the size of *this and ilist - O(size() + ilist.size()) .

Exceptions ​

• until C++17
• (1, 2) May throw implementation-defined exceptions.
• (3) Noexcept specification:

After container move assignment (overload (2) ), unless element-wise move assignment is forced by incompatible allocators, references, pointers, and iterators (other than the end iterator) to other remain valid, but refer to elements that are now in *this . The current standard makes this guarantee via the blanket statement in [container.requirements.general]/12 , and a more direct guarantee is under consideration via LWG 2321 .

• Return value

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Assignment Operators in C

In C language, the assignment operator stores a certain value in an already declared variable. A variable in C can be assigned the value in the form of a literal, another variable, or an expression.

The value to be assigned forms the right-hand operand, whereas the variable to be assigned should be the operand to the left of the " = " symbol, which is defined as a simple assignment operator in C.

In addition, C has several augmented assignment operators.

The following table lists the assignment operators supported by the C language −

Simple Assignment Operator (=)

The = operator is one of the most frequently used operators in C. As per the ANSI C standard, all the variables must be declared in the beginning. Variable declaration after the first processing statement is not allowed.

You can declare a variable to be assigned a value later in the code, or you can initialize it at the time of declaration.

You can use a literal, another variable, or an expression in the assignment statement.

Once a variable of a certain type is declared, it cannot be assigned a value of any other type. In such a case the C compiler reports a type mismatch error.

In C, the expressions that refer to a memory location are called "lvalue" expressions. A lvalue may appear as either the left-hand or right-hand side of an assignment.

On the other hand, the term rvalue refers to a data value that is stored at some address in memory. A rvalue is an expression that cannot have a value assigned to it which means an rvalue may appear on the right-hand side but not on the left-hand side of an assignment.

Variables are lvalues and so they may appear on the left-hand side of an assignment. Numeric literals are rvalues and so they may not be assigned and cannot appear on the left-hand side. Take a look at the following valid and invalid statements −

Augmented Assignment Operators

In addition to the = operator, C allows you to combine arithmetic and bitwise operators with the = symbol to form augmented or compound assignment operator. The augmented operators offer a convenient shortcut for combining arithmetic or bitwise operation with assignment.

For example, the expression "a += b" has the same effect of performing "a + b" first and then assigning the result back to the variable "a".

Run the code and check its output −

Similarly, the expression "a <<= b" has the same effect of performing "a << b" first and then assigning the result back to the variable "a".

Here is a C program that demonstrates the use of assignment operators in C −

When you compile and execute the above program, it will produce the following result −

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Commonly Used Methods

• vector::begin() and vector::end() in C++ STL
• vector::empty() and vector::size() in C++ STL
• vector::operator= and vector::operator[ ] in C++ STL
• vector::front() and vector::back() in C++ STL
• vector::push_back() and vector::pop_back() in C++ STL
• vector insert() Function in C++ STL
• vector emplace() function in C++ STL

vector :: assign() in C++ STL

• vector erase() and clear() in C++

Other Member Methods

• vector max_size() function in C++ STL
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• vector :: cbegin() and vector :: cend() in C++ STL
• vector::crend() & vector::crbegin() with example
• vector : : resize() in C++ STL
• vector shrink_to_fit() function in C++ STL
• Using std::vector::reserve whenever possible
• vector data() function in C++ STL
• 2D Vector In C++ With User Defined Size
• Passing Vector to a Function in C++
• How does a vector work in C++?
• How to implement our own Vector Class in C++?
• Advantages of vector over array in C++

Common Vector Programs

• Sorting a vector in C++
• How to reverse a Vector using STL in C++?
• How to find the minimum and maximum element of a Vector using STL in C++?
• How to find index of a given element in a Vector in C++

vector:: assign() is an STL in C++ which assigns new values to the vector elements by replacing old ones. It can also modify the size of the vector if necessary.

The syntax for assigning constant values: 

Program 1: The program below shows how to assign constant values to a vector 

The syntax for assigning values from an array or list: 

Program 2: The program below shows how to assign values from an array or list 

The syntax for modifying values from a vector  

Program 3: The program below shows how to modify the vector 

Time Complexity – Linear O(N)

Syntax for assigning values with initializer list:

Program 4:The program below shows how to assign a vector with an initializer list.

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cppreference.com

Assignment operators.

Assignment operators modify the value of the object.

[ edit ] Definitions

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

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

Compound assignment 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 ] Assignment operator syntax

The assignment expressions have the form

• ↑ target-expr must have higher precedence than an assignment expression.
• ↑ new-value cannot be a comma expression, because its precedence is lower.

[ edit ] Built-in simple assignment operator

For the built-in simple assignment, the object referred to by target-expr is modified by replacing its value with the result of new-value . target-expr must be a modifiable lvalue.

The result of a built-in simple assignment is an lvalue of the type of target-expr , referring to target-expr . If target-expr is a bit-field , the result is also a bit-field.

[ edit ] Assignment from an expression

If new-value is an expression, it is implicitly converted to the cv-unqualified type of target-expr . When target-expr is a bit-field that cannot represent the value of the expression, the resulting value of the bit-field is implementation-defined.

If target-expr and new-value identify overlapping objects, the behavior is undefined (unless the overlap is exact and the type is the same).

In overload resolution against user-defined operators , 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:

[ edit ] Built-in compound assignment operator

The behavior of every built-in compound-assignment expression target-expr   op   =   new-value is exactly the same as the behavior of the expression target-expr   =   target-expr   op   new-value , except that target-expr is evaluated only once.

The requirements on target-expr and new-value of built-in simple assignment operators also apply. Furthermore:

• For + = and - = , the type of target-expr must be an arithmetic type or a pointer to a (possibly cv-qualified) completely-defined object type .
• For all other compound assignment operators, the type of target-expr must be an arithmetic type.

In overload resolution against user-defined operators , 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:

[ edit ] Example

Possible output:

[ edit ] Defect reports

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

[ edit ] See also

Operator precedence

Operator overloading

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