std::pmr::set_default_resource
来自 cppreference.cn
| 定义于头文件 <memory_resource> |
||
| std::pmr::memory_resource* set_default_resource( std::pmr::memory_resource* r ) noexcept; |
(自 C++17 起) | |
如果 r 非空，则将默认内存资源指针设为 r；否则，将默认内存资源指针设为 std::pmr::new_delete_resource()。
默认内存资源指针 由某些设施在未显式提供内存资源时使用。初始默认内存资源指针是 std::pmr::new_delete_resource 的返回值。
此函数是线程安全的。每次调用 std::pmr::set_default_resource 都与后续的 std::pmr::set_default_resource 和 std::pmr::get_default_resource 调用同步（见 std::memory_order）。
[编辑] 返回值
返回默认内存资源指针的先前值。
[编辑] 示例
运行此代码
#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{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"; } }
可能的输出
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
[编辑] 参见
| (C++17) |
获取默认的 std::pmr::memory_resource (函数) |
| (C++17) |
返回一个静态的程序范围 std::pmr::memory_resource，它使用全局 operator new 和 operator delete 来分配和释放内存 (函数) |
