std::allocator<T>:: deallocate

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.

Parameters

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();

See also