std::pmr::set_default_resource
From cppreference.com
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_resourcesynchronizes with (see std::memory_order) the subsequent std::pmr::set_default_resource and std::pmr::get_default_resource calls.
[edit]Return value
Returns the previous value of the default memory resource pointer.
[edit]Example
Run this code
#include <array>#include <cstddef>#include <cstdint>#include <iostream>#include <iterator>#include <memory_resource>#include <vector> class noisy_allocator :publicstd::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';returnstd::pmr::new_delete_resource()->deallocate(p, bytes, alignment);} bool do_is_equal(conststd::pmr::memory_resource& other)constnoexcept override {returnstd::pmr::new_delete_resource()->is_equal(other);}}; int main(){constexprint push_back_limit{16}; noisy_allocator mem; std::pmr::set_default_resource(&mem); {std::cout<<"Entering scope #1 (without buffer on stack)...\n";std::cout<<"Creating vector v...\n";std::pmr::vector<std::uint16_t> v{1, 2, 3, 4};std::cout<<"v.data() @ "<< v.data()<<'\n'; std::cout<<"Requesting more...\n";for(int i{0}; i != push_back_limit;++i){ v.push_back(i);std::cout<<"v.size(): "<< v.size()<<'\n';}std::cout<<"Exiting scope #1...\n";} std::cout<<'\n'; {std::cout<<"Entering scope #2 (with buffer on stack)...\n"; std::uint8_t buffer[16];std::cout<<"Allocating buffer on stack: "<< sizeof buffer <<" bytes @ "<<static_cast<void*>(buffer)<<'\n';std::pmr::monotonic_buffer_resource mem_res{std::data(buffer), std::size(buffer)}; std::cout<<"Creating vector v...\n";std::pmr::vector<std::uint16_t> v{{1, 2, 3, 4}, &mem_res};std::cout<<"v.data() @ "<< v.data()<<'\n';// equals to `buffer` address std::cout<<"Requesting more...\n";for(int i{0}; i != push_back_limit;++i){ v.push_back(i);std::cout<<"v.size(): "<< v.size()<<'\n';}std::cout<<"Exiting scope #2...\n";}}
Possible output:
Entering scope #1 (without buffer on stack)... Creating vector v... + Allocating 8 bytes @ 0x1f75c30 v.data() @ 0x1f75c30 Requesting more... + Allocating 16 bytes @ 0x1f75c50 - Deallocating 8 bytes @ 0x1f75c30 v.size(): 5 v.size(): 6 v.size(): 7 v.size(): 8 + Allocating 32 bytes @ 0x1f75c70 - Deallocating 16 bytes @ 0x1f75c50 v.size(): 9 v.size(): 10 v.size(): 11 v.size(): 12 v.size(): 13 v.size(): 14 v.size(): 15 v.size(): 16 + Allocating 64 bytes @ 0x1f75ca0 - Deallocating 32 bytes @ 0x1f75c70 v.size(): 17 v.size(): 18 v.size(): 19 v.size(): 20 Exiting scope #1... - Deallocating 64 bytes @ 0x1f75ca0 Entering scope #2 (with buffer on stack)... Allocating buffer on stack: 16 bytes @ 0x7fffbe9f8240 Creating vector v... v.data() @ 0x7fffbe9f8240 Requesting more... + Allocating 64 bytes @ 0x1f75ca0 v.size(): 5 v.size(): 6 v.size(): 7 v.size(): 8 v.size(): 9 v.size(): 10 v.size(): 11 v.size(): 12 v.size(): 13 v.size(): 14 v.size(): 15 v.size(): 16 + Allocating 128 bytes @ 0x1f75cf0 v.size(): 17 v.size(): 18 v.size(): 19 v.size(): 20 Exiting scope #2... - Deallocating 128 bytes @ 0x1f75cf0 - Deallocating 64 bytes @ 0x1f75ca0
[edit]See also
(C++17) | gets the default std::pmr::memory_resource (function) |
(C++17) | returns a static program-wide std::pmr::memory_resource that uses the global operator new and operator delete to allocate and deallocate memory (function) |
