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

std::unique_ptr<T,Deleter>::reset - cppreference.com

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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.

1,2) Equivalent to auto old_ptr = get();
/* assigns “ptr” to the stored pointer */
if (old_ptr)
get_deleter()(old_ptr);.

If get_deleter()(old_ptr) throws an exception, the behavior is undefined.

2) This overload participates in overload resolution only if U is the same type as pointer, or all following conditions are satisfied:

pointer is the same type as element_type*.
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

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

#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
LWG 2169	C++11	the overload `unique_ptr<T[]>::reset(pointer)` existed	removed the overload

Parameters

Notes

Example

Defect reports

See also