FreeBSD Manual Pages
std::pointer_traits(3) C++ Standard Libary std::pointer_traits(3) NAME std::pointer_traits - std::pointer_traits Synopsis Defined in header <memory> template< class Ptr > struct pointer_traits; (1) (since C++11) template< class T > struct pointer_traits<T*>; (2) (since C++11) The pointer_traits class template provides the standardized way to access certain properties of pointer-like types (fancy pointers, such as boost::interprocess::offset_ptr). The standard template std::alloca- tor_traits relies on pointer_traits to determine the defaults for various typedefs re- quired by Allocator. 1) The non-specialized pointer_traits declares the following types: Member types Type Definition pointer Ptr Ptr::element_type if present. Otherwise T if Ptr is a template element_type specialization Template<T, Args...>. Otherwise, the pointer_traits specialization is ill-formed difference_type Ptr::difference_type if present, otherwise std::ptrdiff_t Member alias templates Template Definition template <class U> using Ptr::rebind<U> if exists, otherwise Tem- plate<U, Args...> if rebind Ptr is a template specialization Tem- plate<T, Args...> Member functions pointer_to obtains a dereferenceable pointer to its argument [static] (public static member function) Optional member functions of program-defined specializations to_address obtains a raw pointer from a fancy pointer (inverse of [static] (C++20)(optional) pointer_to) (public static member function) 2) A specialization is provided for pointer types, T*, which de- clares the following types: Member types Type Definition pointer T* element_type T difference_type std::ptrdiff_t Member alias templates Template Definition template< class U > using rebind U* Member functions pointer_to obtains a dereferenceable pointer to its argument [static] (public static member function) Notes The rebind member template alias makes it possible, given a pointer- like type that points to T, to obtain the same pointer-like type that points to U. For example, using another_pointer = std::pointer_traits<std::shared_ptr<int>>::re- bind<double>; static_assert(std::is_same<another_pointer, std::shared_ptr<dou- ble>>::value); A specialization for user-defined fancy pointer types may provide an additional static member function to_address to customize the behav- ior (since C++20) of std::to_address. Feature-test macro: __cpp_lib_constexpr_memory Example // Run this code #include <memory> #include <iostream> template <class Ptr> struct BlockList { // Predefine a memory block struct block; // Define a pointer to a memory block from the kind of pointer Ptr s // If Ptr is any kind of T*, block_ptr_t is block* // If Ptr is smart_ptr<T>, block_ptr_t is smart_ptr<block> using block_ptr_t = typename std::pointer_traits<Ptr>::template re- bind<block>; struct block { std::size_t size{}; block_ptr_t next_block{}; }; block_ptr_t free_blocks; }; int main() { [[maybe_unused]] BlockList<int*> bl1; // The type of bl1.free_blocks is BlockList<int*>:: block* BlockList<std::shared_ptr<char>> bl2; // The type of bl2.free_blocks is // std::shared_ptr< BlockList<std::shared_ptr<char> >::block> std::cout << bl2.free_blocks.use_count() << '\n'; } Output: 0 See also allocator_traits provides information about allocator types (C++11) (class template) addressof obtains actual address of an object, even if the & operator is (C++11) overloaded (function template) http://cppreference.com 2022.07.31 std::pointer_traits(3)
NAME | Synopsis | Member types | Member alias templates | Member functions | Member types | Member alias templates | Member functions | Notes | Example | Output: | See also
Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=std::pointer_traits&sektion=3&manpath=FreeBSD+Ports+15.0>