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std::out_ptr(3) C++ Standard Libary std::out_ptr(3) NAME std::out_ptr - std::out_ptr Synopsis Defined in header <memory> template< class Pointer = void, class Smart, class... Args > (since C++23) auto out_ptr( Smart& s, Args&&... args ); Returns an std::out_ptr_t with deduced template arguments that cap- tures arguments for resetting by reference. The program is ill-formed if construction of the return value (see below) is ill-formed. Parameters s - the object (typically a smart pointer) to adapt args... - the arguments for resetting to capture Return value std::out_ptr_t<Smart, P, Args&&>(s, std::forward<Args>(args)...), where P is * Pointer, if Pointer is not same as void. Otherwise, * Smart::pointer, if it is valid and denotes a type. Otherwise, * Smart::element_type*, if Smart::element_type is valid and de- notes a type. Otherwise, * std::pointer_traits<Smart>::element_type*. Notes Users may specify the template argument for the template parameter Pointer, in order to interoperate with foreign functions that take a Pointer*. As all arguments for resetting are captured by reference, the re- turned out_ptr_t should be a temporary object destroyed at the end of the full-ex- pression containing the call to the foreign function, in order to avoid dangling refer- ences. Feature-test macro Value Std Feature __cpp_lib_out_ptr 202106L (C++23) std::out_ptr, std::inout_ptr 202311L (C++26) freestanding std::out_ptr and std::inout_ptr Example Use std::out_ptr to adapt a smart pointer for sqlite3_open, which expects a sqlite3** as an out parameter. // Run this code #include <memory> #include <sqlite3.h> int main() { auto close_db = [](sqlite3* db) { sqlite3_close(db); }; { // open an in-memory database, and manage its lifetime with std::unique_ptr std::unique_ptr<sqlite3, decltype(close_db)> up; sqlite3_open(":memory:", std::out_ptr(up)); sqlite3* db = up.get(); // do something with db ... } { // same as above, but use a std::shared_ptr std::shared_ptr<sqlite3> sp; sqlite3_open(":memory:", std::out_ptr(sp, close_db)); sqlite3* db = sp.get(); // do something with db ... } } See also inout_ptr creates an inout_ptr_t with an associated smart pointer (C++23) and resetting arguments (function template) make_unique make_unique_for_overwrite creates a unique pointer that manages a new object (C++14) (function template) (C++20) make_shared creates a shared pointer that manages a new object make_shared_for_overwrite (function template) (C++20) http://cppreference.com 2024.06.10 std::out_ptr(3)
NAME | Synopsis | Parameters | Return value | Notes | Example | See also
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