std::pmr::set_default_resource

 

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Defined in header <memory_resource>
std::pmr::memory_resource* set_default_resource( std::pmr::memory_resource* r ) noexcept;		(since C++17)

If r is not null, sets the default memory resource pointer to r; otherwise, sets the default memory resource pointer to std::pmr::new_delete_resource().

The default memory resource pointer is used by certain facilities when an explicit memory resource is not supplied. The initial default memory resource pointer is the return value of std::pmr::new_delete_resource.

This function is thread-safe. Every call to std::pmr::set_default_resource synchronizes with (see std::memory_order) the subsequent std::pmr::set_default_resource and std::pmr::get_default_resource calls.

Return value

Returns the previous value of the default memory resource pointer.

Example

Run this code

#include <array>
#include <cstddef>
#include <cstdint>
#include <iostream>
#include <iterator>
#include <memory_resource>
#include <vector>

class noisy_allocator : public std::pmr::memory_resource
{
    void* do_allocate(std::size_t bytes, std::size_t alignment) override
    {
        std::cout << "+ Allocating " << bytes << " bytes @ ";
        void* p = std::pmr::new_delete_resource()->allocate(bytes, alignment);
        std::cout << p << '\n';
        return p;
    }

    void do_deallocate(void* p, std::size_t bytes, std::size_t alignment) override
    {
        std::cout << "- Deallocating " << bytes << " bytes @ " << p << '\n';
        return std::pmr::new_delete_resource()->deallocate(p, bytes, alignment);
    }

    bool do_is_equal(const std::pmr::memory_resource& other) const noexcept override
    {
        return std::pmr::new_delete_resource()->is_equal(other);
    }
};

int main()
{
    constexpr int push_back_limit