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

 

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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> queue;const S& s = queue.emplace(42, 3.14, "C++");// for return value C++17 requiredstd::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)