std::allocator::construct(3)

💅 std::allocator::construct(3) 💅

okay so bestie, welcome to the std::allocator::construct(3) page from the C++ Standard Library manual. this one is a little vintage, a little deprecated, and honestly kind of iconic in a “we used to do it this way” way. let’s get into it 💖

✨ NAME ✨

std::allocator::construct — std::allocator::construct (yes, the name is literally the name, periodt 👑

🎀 Synopsis 🎀

Defined in header <memory> — noted, bestie 📌

void construct( pointer p, const_reference val ); (1) (until C++11)
template< class U, class... Args >                    (since C++11)
void construct( U* p, Args&&... args );           (2) (deprecated in C++17)
                                                          (removed in C++20)

okay so what does it do? it constructs an object of type T in allocated uninitialized storage pointed to by p, using global placement-new. the way that this is literally placement-new with extra steps is sending me 😭

1. Calls ::new((void*)p) T(val).
2. Calls ::new((void*)p) U(std::forward<Args>(args)...).

⚠️ heads up: overload (2) is deprecated in C++17 and removed in C++20 — not me being dramatic, that’s just the timeline 😭

🌸 Parameters 🌸

• p — pointer to allocated uninitialized storage
• val — the value to use as the copy constructor argument
• args... — the constructor arguments to use

that’s the whole squad, no cap 🫶

💖 Return value 💖

(none) — literally nothing comes back, bestie. it’s giving void energy 🫶

🫶 Defect reports 🫶

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

• LWG 402 — Applied to: C++98. Behavior as published: if T::operator new exists, the program might be ill-formed. Correct behavior: uses global replacement-new instead. 🔧

🔥 See also 🔥

• construct [static] — constructs an object in the allocated storage (function template)
• construct_at (C++20) — creates an object at a given address (function template)
• operator new — allocation functions
• operator new[] — (function)

mwah 💋 — source: http://cppreference.com — version/date: 2024.06.10 — std::allocator::construct(3) 🎀