std::queue<T,Container>::emplace

 

C++

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Named requirements

Feature test macros (C++20)

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Technical specifications

Symbols index

External libraries

 

Containers library

Sequence

array (C++11)

vector

deque

forward_list (C++11)

list

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set

multiset

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multimap

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unordered_set (C++11)

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unordered_map (C++11)

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stack

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span (C++20)

 

std::queue

Member functions

queue::queue

queue::~queue

queue::operator=

Element access

queue::front

queue::back

Capacity

queue::empty

queue::size

Modifiers

queue::push

queue::emplace (C++11)

queue::pop

queue::swap (C++11)

Non-member functions

operator==operator!=operator<operator>operator<=operator>=operator<=> (C++20)

std::swap

Deduction guides(C++17)

 

template< class... Args > void emplace( Args&&... args );		(since C++11) (until C++17)
template< class... Args > decltype(auto) emplace( Args&&... args );		(since C++17)

Pushes a new element to the end of the queue. The element is constructed in-place, i.e. no copy or move operations are performed. The constructor of the element is called with exactly the same arguments as supplied to the function.

Effectively calls c.emplace_back(std::forward<Args>(args)...);

Parameters

args

-

arguments to forward to the constructor of the element

Return value

(none)	(until C++17)
The value or reference, if any, returned by the above call to Container::emplace_back.	(since C++17)

Complexity

Identical to the complexity of Container::emplace_back.

Example

Run this code

#include <iostream>
#include <queue>
 
struct S
{
    int id;
 
    S(int i, double d, std::string s) : id{i}
    {
        std::cout << "S::S(" << i << ", " << d << ", \"" << s << "\");\n";
    }
};
 
int main()
{
    std::queue<S> adaptor;
 
    const S& s = adaptor.emplace(42, 3.14, "C++"); // for return value C++17 required
 
    std::cout << "id = " << s.id << '\n';
}

Output:

S::S(42, 3.14, "C++")
id = 42

Defect reports

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

DR	Applied to	Behavior as published	Correct behavior
LWG 2783	C++17	emplace returned reference, breaking compatibility with pre-C++17 containers	returns decltype(auto)

See also

push	inserts element at the end (public member function)
pop	removes the first element (public member function)