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

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< cpp‎ | memory‎ | unique ptr

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

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

### See also

release | returns a pointer to the managed object and releases the ownership (public member function)

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