# std::unique_ptr::reset

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< cpp‎ | memory‎ | unique ptr

members of the primary template, unique_ptr<T> |  |
void reset( pointer ptr = pointer() ); | (1) |
members of the specialization unique_ptr<T[]> |  |
void reset( pointer ptr = pointer() ); | (2) | (until C++17)
| (3) |
template< class U > void reset( U ) = delete; |  | (until C++17)
template< class U > void reset( U ); |  | (since C++17)
| (4) |
void reset( std::nullptr_t p ); |  | (until C++17)
void reset( std::nullptr_t p = nullptr ); |  | (since C++17)

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 != nullptr) get_deleter()(old_ptr).

2) Behaves the same as the reset member of the primary template.
3) In the specialization for dynamic arrays, std::unique_ptr<T[]>, this template member is provided to prevent using reset() with a pointer to derived (which would result in undefined behavior with arrays).
4) In the specialization for dynamic arrays, std::unique_ptr<T[]>, this overload is necessary to allow reset to nullptr (which would otherwise be prohibited by the template overload). Equivalent to reset(pointer())

(until C++17)

3) 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(*)[]`.

4) Equivalent to reset(pointer())

(since C++17)

### Parameters

ptr | - | pointer to a new object to manage

### Return value

(none)

### Exceptions

`noexcept` specification:
noexcept

### 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 {
        Foo() { std::cout << "Foo...\n"; }
        ~Foo() { std::cout << "~Foo...\n"; }
    };

    struct D {
        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...

### See also

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

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