NAME

std::queue::emplace - std::queue::emplace

Synopsis

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

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 (since C++17)
Container::emplace_back.

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 returns decltype(auto)
compatibility with pre-C++17 containers