std::allocator<T>::deallocate

 

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Technical Specifications

 

Dynamic memory management

Smart pointers unique_ptr (C++11) shared_ptr (C++11) weak_ptr (C++11) auto_ptr (until C++17) owner_less (C++11) enable_shared_from_this (C++11) bad_weak_ptr (C++11) default_delete (C++11) Allocators allocator allocator_traits (C++11) allocator_arg_t (C++11) allocator_arg (C++11) uses_allocator (C++11) uses_allocator_construction_args (C++20) make_obj_using_allocator (C++20) uninitialized_construct_using_allocator (C++20) scoped_allocator_adaptor (C++11) pmr::polymorphic_allocator (C++17) Memory resources pmr::memory_resource (C++17) pmr::get_default_resource (C++17) pmr::set_default_resource (C++17) pmr::new_delete_resource (C++17) pmr::null_memory_resource (C++17) pmr::synchronized_pool_resource (C++17) pmr::unsynchronized_pool_resource (C++17) pmr::monotonic_buffer_resource (C++17) pmr::pool_options (C++17) Uninitialized storage raw_storage_iterator (until C++20) get_temporary_buffer (until C++20) return_temporary_buffer (until C++20)

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std::allocator

Member functions

allocator::allocator

allocator::~allocator

allocator::address (until C++20)

allocator::allocate

allocator::deallocate

allocator::max_size (until C++20)

allocator::construct (until C++20)

allocator::destroy (until C++20)

Non-member functions

operator==operator!= (until C++20)

 

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().

The argument n must be equal to the first argument of the call to allocate() that originally produced p; 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)

Parameters

p	-	pointer obtained from allocate()
n	-	number of objects earlier passed to allocate()

Return value

(none)

Example

Run this code

#include <algorithm>
#include <iostream>
#include <memory>
 
class S {
    inline static int n{1};
    int m{};
    void pre() const { std::cout << "#" << 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;
    S* s = allocator.allocate(n);
 
    for (std::size_t i = 0; i != n; ++i) {
        // allocator.construct(&s[i], i+2); // removed in C++20
        std::construct_at(&s[i], i+2); // since C++20
    }
 
    std::for_each(s, s + n, [](const auto& e) { e.id(); });
 
    std::destroy_n(s, n);
 
    allocator.deallocate(s, n);
}

Output:

#1 S::S(2);
#2 S::S(3);
#3 S::S(4);
#4 S::S(5);
#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

allocate	allocates uninitialized storage (public member function)
deallocate [static]	deallocates storage using the allocator (public static member function of std::allocator_traits<Alloc>)