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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) | |
Ifr is not null, sets the default memory resource pointer tor; otherwise, sets the default memory resource pointer tostd::pmr::new_delete_resource().
Thedefault 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 ofstd::pmr::new_delete_resource.
This function is thread-safe. Every call tostd::pmr::set_default_resourcesynchronizes with (seestd::memory_order) the subsequentstd::pmr::set_default_resource andstd::pmr::get_default_resource calls.
Returns the previous value of the default memory resource pointer.
#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 @ 0x1f75c30v.data() @ 0x1f75c30Requesting more...+ Allocating 16 bytes @ 0x1f75c50- Deallocating 8 bytes @ 0x1f75c30v.size(): 5v.size(): 6v.size(): 7v.size(): 8+ Allocating 32 bytes @ 0x1f75c70- Deallocating 16 bytes @ 0x1f75c50v.size(): 9v.size(): 10v.size(): 11v.size(): 12v.size(): 13v.size(): 14v.size(): 15v.size(): 16+ Allocating 64 bytes @ 0x1f75ca0- Deallocating 32 bytes @ 0x1f75c70v.size(): 17v.size(): 18v.size(): 19v.size(): 20Exiting scope #1...- Deallocating 64 bytes @ 0x1f75ca0 Entering scope #2 (with buffer on stack)...Allocating buffer on stack: 16 bytes @ 0x7fffbe9f8240Creating vector v...v.data() @ 0x7fffbe9f8240Requesting more...+ Allocating 64 bytes @ 0x1f75ca0v.size(): 5v.size(): 6v.size(): 7v.size(): 8v.size(): 9v.size(): 10v.size(): 11v.size(): 12v.size(): 13v.size(): 14v.size(): 15v.size(): 16+ Allocating 128 bytes @ 0x1f75cf0v.size(): 17v.size(): 18v.size(): 19v.size(): 20Exiting scope #2...- Deallocating 128 bytes @ 0x1f75cf0- Deallocating 64 bytes @ 0x1f75ca0
(C++17) | gets the defaultstd::pmr::memory_resource (function)[edit] |
(C++17) | returns a static program-widestd::pmr::memory_resource that uses the globaloperator new andoperator delete to allocate and deallocate memory (function)[edit] |
