std::unique_ptr::reset - cppreference.com

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# std::unique_ptr::reset

From cppreference.com
< cpp‎ | memory‎ | unique ptr

void reset( pointer ptr = pointer() ); | (1) | (since C++11)
template< class U > void reset( U ) = delete; | (2) | (since C++11) (member of specialization unique_ptr<T[]> only)
void reset( std::nullptr_t p ); | (3) | (since C++11) (member of specialization unique_ptr<T[]> only)

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) 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).
3) In the specialization for dynamic arrays, std::unique_ptr<T[]>, the third overload is necessary to allow reset to nullptr (which would otherwise be prohibited by the template overload). Equivalent to reset(pointer())

### [edit] Parameters

ptr | - | pointer to a new object to manage

### [edit] Return value

(none)

### [edit] Exceptions

`noexcept` specification:
noexcept

### [edit] 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.

Visual Studio's implementation of reset is currently (in VC10 and VC11) broken and non-conforming to the C++11 standard. It deletes the managed object before resetting the pointer to the owned object.

### [edit] 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...

### [edit] See also

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

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Category:

- unconditionally noexcept