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# std::shared_ptr::reset

From cppreference.com
< cpp‎ | memory‎ | shared ptr

void reset(); | (1) | (since C++11)
template< class Y > void reset( Y* ptr ); | (2) | (since C++11)
template< class Y, class Deleter > void reset( Y* ptr, Deleter d ); | (3) | (since C++11)
template< class Y, class Deleter, class Alloc > void reset( Y* ptr, Deleter d, Alloc alloc ); | (4) | (since C++11)

Replaces the managed object with an object pointed to by `ptr`. Optional deleter `d` can be supplied, which is later used to destroy the new object when no `shared_ptr` objects own it. By default, `delete` expression is used as deleter. Proper `delete` expression corresponding to the supplied type is always selected, this is the reason why the function is implemented as template using a separate parameter `Y`.

If `*this` already owns an object and it is the last `shared_ptr` owning it, the object is destroyed through the owned deleter.

If the object pointed to by `ptr` is already owned, the function results in undefined behavior.

1) Releases the ownership of the managed object, if any. After the call, *this manages no object. Equivalent to shared_ptr().swap(*this);
2-4) Replaces the managed object with an object pointed to by `ptr`. `Y` must be a complete type and implicitly convertible to `T`. Additionally:
2) Uses the delete expression as the deleter. A valid delete expression must be available, i.e. delete ptr must be well formed, have well-defined behavior and not throw any exceptions. Equivalent to shared_ptr<T>(ptr).swap(*this);.
3) Uses the specified deleter `d` as the deleter. `Deleter` must be callable for the type `T`, i.e. d(ptr) must be well formed, have well-defined behavior and not throw any exceptions. `Deleter` must be `CopyConstructible`, and its copy constructor and destructor must not throw exceptions. Equivalent to shared_ptr<T>(ptr, d).swap(*this);.
4) Same as (3), but additionally uses a copy of `alloc` for allocation of data for internal use. `Alloc` must be a `Allocator`. The copy constructor and destructor must not throw exceptions. Equivalent to shared_ptr<T>(ptr, d, alloc).swap(*this);.

### [edit] Parameters

ptr | - | pointer to an object to acquire ownership of
d | - | deleter to store for deletion of the object
alloc | - | allocator to use for internal allocations

### [edit] Return value

(none)

### [edit] Exceptions

1)
`noexcept` specification:
noexcept
2) std::bad_alloc if required additional memory could not be obtained. May throw implementation-defined exception for other errors. delete ptr is called if an exception occurs.
3-4) std::bad_alloc if required additional memory could not be obtained. May throw implementation-defined exception for other errors. d(ptr) is called if an exception occurs.

### [edit] Example

Run this code

    #include <memory>
    #include <iostream>

    struct Foo {
        Foo(int n = 0) noexcept : bar(n) {
            std::cout << "Foo: constructor, bar = " << bar << '\n';
        }
        ~Foo() {
             std::cout << "Foo: destructor, bar = " << bar << '\n';
        }
        int getBar() const noexcept { return bar; }
    private:
        int bar;
    };

    int main()
    {
        std::shared_ptr<Foo> sptr = std::make_shared<Foo>(1);
        std::cout << "The first Foo's bar is " << sptr->getBar() << "\n";

        // reset the shared_ptr, hand it a fresh instance of Foo
        // (the old instance will be destroyed after this call)
        sptr.reset(new Foo);
        std::cout << "The second Foo's bar is " << sptr->getBar() << "\n";
    }

Output:

    Foo: constructor, bar = 1
    The first Foo's bar is 1
    Foo: constructor, bar = 0
    Foo: destructor, bar = 1
    The second Foo's bar is 0
    Foo: destructor, bar = 0

### [edit] See also

(constructor) | constructs new `shared_ptr` (public member function) [edit]

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Category:

- unconditionally noexcept