void deallocate( T* p, std::size_t n ); | (until C++20) | |
constexpr void deallocate( T* p, std::size_t n ); | (since C++20) |
Deallocates the storage referenced by the pointer p, which must be a pointer obtained by an earlier call to allocate() or allocate_at_least() (since C++23).
The argument n must be equal to the first argument of the call to allocate() that originally produced p, or in the range [m, count] if p is obtained from a call to allocate_at_least(m) which returned {p, count} (since C++23); otherwise, the behavior is undefined.
Calls ::operator delete(void*) or ::operator delete(void*, std::align_val_t) (since C++17), but it is unspecified when and how it is called.
| In evaluation of a constant expression, this function must deallocate storage allocated within the evaluation of the same expression. | (since C++20) |
| p | - | pointer obtained from allocate() or allocate_at_least() (since C++23) |
| n | - | number of objects earlier passed to allocate(), or a number between requested and actually allocated number of objects via allocate_at_least() (may be equal to either bound) (since C++23) |
(none).
#include <algorithm>
#include <cstddef>
#include <iostream>
#include <memory>
#include <string>
class S
{
inline static int n{1};
int m{};
void pre() const { std::cout << "#" << m << std::string(m, ' '); }
public:
S(int x) : m{n++} { pre(); std::cout << "S::S(" << x << ");\n"; }
~S() { pre(); std::cout << "S::~S();\n"; }
void id() const { pre(); std::cout << "S::id();\n"; }
};
int main()
{
constexpr std::size_t n{4};
std::allocator<S> allocator;
try
{
S* s = allocator.allocate(n); // may throw
for (std::size_t i{}; i != n; ++i)
{
// allocator.construct(&s[i], i + 42); // removed in C++20
std::construct_at(&s[i], i + 42); // since C++20
}
std::for_each_n(s, n, [](const auto& e) { e.id(); });
std::destroy_n(s, n);
allocator.deallocate(s, n);
}
catch (std::bad_array_new_length const& ex) { std::cout << ex.what() << '\n'; }
catch (std::bad_alloc const& ex) { std::cout << ex.what() << '\n'; }
}Output:
#1 S::S(42); #2 S::S(43); #3 S::S(44); #4 S::S(45); #1 S::id(); #2 S::id(); #3 S::id(); #4 S::id(); #1 S::~S(); #2 S::~S(); #3 S::~S(); #4 S::~S();
| allocates uninitialized storage (public member function) |
|
|
(C++23) | allocates uninitialized storage at least as large as requested size (public member function) |
|
[static] | deallocates storage using the allocator (public static member function of std::allocator_traits<Alloc>) |
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