NAME

std::unique_ptr::reset - std::unique_ptr::reset

Synopsis

members of the primary template, unique_ptr<T>
void reset( pointer ptr = pointer() ) noexcept; (1) (constexpr since C++23)
members of the specialization unique_ptr<T[]>
template< class U > (2) (constexpr since C++23)
void reset( U ptr ) noexcept;
void reset( std::nullptr_t = nullptr ) noexcept; (3) (constexpr since C++23)

Replaces the managed object.

1) Given current_ptr, the pointer that was managed by *this, performs the following
actions, in this order:

1. Saves a copy of the current pointer old_ptr = current_ptr
2. Overwrites the current pointer with the argument current_ptr = ptr
3. If the old pointer was non-empty, deletes the previously managed object
if(old_ptr) get_deleter()(old_ptr).

2) Behaves the same as the reset member of the primary template, except that it will
only participate in overload resolution if either

1. U is the same type as pointer, or
2. pointer is the same type as element_type* and U is a pointer type V* such that
V(*)[] is convertible to element_type(*)[].

3) Equivalent to reset(pointer())

Parameters

ptr - pointer to a new object to manage

Return value

(none)

Notes

To replace the managed object while supplying a new deleter as well, move assignment
operator may be used.

A test for self-reset, i.e. whether ptr points to an object already managed by
*this, is not performed, except where provided as a compiler extension or as a
debugging assert. Note that code such as p.reset(p.release()) does not involve
self-reset, only code like p.reset(p.get()) does.

Example

// Run this code

#include <iostream>
#include <memory>

struct Foo { // object to manage
Foo() { std::cout << "Foo...\n"; }
~Foo() { std::cout << "~Foo...\n"; }
};

struct D { // deleter
void operator() (Foo* p) {
std::cout << "Calling delete for Foo object... \n";
delete p;
}
};

int main()
{
std::cout << "Creating new Foo...\n";
std::unique_ptr<Foo, D> up(new Foo(), D()); // up owns the Foo pointer (deleter D)

std::cout << "Replace owned Foo with a new Foo...\n";
up.reset(new Foo()); // calls deleter for the old one

std::cout << "Release and delete the owned Foo...\n";
up.reset(nullptr);
}

Output:

Creating new Foo...
Foo...
Replace owned Foo with a new Foo...
Foo...
Calling delete for Foo object...
~Foo...
Release and delete the owned Foo...
Calling delete for Foo object...
~Foo...

Defect reports

The following behavior-changing defect reports were applied retroactively to
previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 2118 C++11 unique_ptr<T[]>::reset rejected qualification accepts
conversions