std::queue<T,Container>::emplace
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C++
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Ranges library (C++20)
Filesystem library (C++17)
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Execution control library (C++26)
Containers library
(C++17)
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(C++26)
(C++26)
(C++11)
(C++11)
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(C++23)
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(C++20)
(C++23)
Tables
std::queue template< class... Args >
void emplace( Args&&... args );
(since C++11) void emplace( Args&&... args );
(until C++17)
template< class... Args >
decltype(auto) emplace( Args&&... 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)...);.
[edit] Parameters
args
-
arguments to forward to the constructor of the element
[edit] Return value
(none)
(until C++17)The value or reference, if any, returned by the above call to Container::emplace_back.
(since C++17)[edit] Complexity
Identical to the complexity of Container::emplace_back.
[edit] 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 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)
|