std::unique_ptr<T,Deleter>::reset

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 > void reset( U ptr ) noexcept;	(2)	(constexpr since C++23)
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:

Saves a copy of the current pointer old_ptr = current_ptr
Overwrites the current pointer with the argument current_ptr = ptr
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

U is the same type as pointer, or
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 conversions	accepts

Compiler support
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Language
Standard library headers
Named requirements
Feature test macros (C++20)
Language support library
Concepts library (C++20)
Metaprogramming library (C++11)
Diagnostics library
General utilities library
Strings library
Containers library
Iterators library
Ranges library (C++20)
Algorithms library
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Technical specifications
Symbols index
External libraries

Member functions
unique_ptr::unique_ptr
unique_ptr::~unique_ptr
unique_ptr::operator=
Modifiers
unique_ptr::release
unique_ptr::reset
unique_ptr::swap
Observers
unique_ptr::get
unique_ptr::get_deleter
unique_ptr::operator bool
unique_ptr::operator*unique_ptr::operator->
unique_ptr::operator[]
Non-member functions
make_uniquemake_unique_for_overwrite (C++14)(C++20)
operator==operator!=operator<operator>operator<=operator>=operator<=> (until C++20)(C++20)
operator<< (C++20)
std::swap
std::hash