std::queue::emplace(3)

💅 std::queue::emplace(3) 💅

okay bestie, this page is from the C++ Standard Libary manual — yes, that spelling, keep it 💖 — and it’s all about making a queue element appear in place like magic ✨

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💖 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.

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

🌸 Parameters 🌸

• args — arguments to forward to the constructor of the element

🎀 Return value 🎀

• until C++17: (none)
• since C++17: The value or reference, if any, returned by the above call to 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> 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 LWG 2783 — applied to C++17. Behavior as published: emplace returned reference, breaking compatibility with pre-C++17 containers. Correct behavior: returns decltype(auto).

🫶 See also 🫶

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

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mwah 💋 — source: http://cppreference.com, version/date: 2024.06.10, page: std::queue::emplace(3) 🎀