std::allocator<T>::deallocate
constexpr void deallocate( T* p, std::size_t n );
void deallocate( T* p, std::size_t n );
Deallocates the storage referenced by the pointer p
, which must be a pointer obtained by an earlier call to
allocate() or allocate_at_least() (od 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}
(od C++23)
otherwise, the behavior is undefined.
Calls ::operator delete(void*)
or ::operator delete(void*, std::align_val_t)
(od 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. (od C++20)
Parameters
p
- pointer obtained from allocate() or allocate_at_least() (od 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) (od C++23)
Return value
(none)
Example
#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'; }
}
#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();