std::out_ptr
<memory>
auto out_ptr( Smart& s, Args&&... args );
Returns an std::out_ptr_t with deduced template arguments that captures arguments for resetting by reference.
The program is ill-formed if construction of the return value (see below) is ill-formed.
Contents
[edit] Parameters
[edit] Return value
std::out_ptr_t <Smart, P, Args&&>(s, std::forward <Args>(args)...), where P is
-
Pointer, ifPointeris not a void type. Otherwise, - Smart::pointer, if it is valid and denotes a type. Otherwise,
- Smart::element_type*, if Smart::element_type is valid and denotes a type. Otherwise,
- std::pointer_traits <Smart>::element_type*.
[edit] 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 returned out_ptr_t should be a temporary object destroyed at the end of the full-expression containing the call to the foreign function, in order to avoid dangling references.
| 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
|
[edit] Example
Use std::out_ptr to adapt a smart pointer for sqlite3_open, which expects a sqlite3** as an out parameter.
#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 ... } }
[edit] See also
inout_ptr_t with an associated smart pointer and resetting arguments (function template) [edit]