std::unique_ptr

 

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std::unique_ptr

Member functions

unique_ptr::unique_ptr

unique_ptr::~unique_ptr

unique_ptr::operator=

Modifiers

unique_ptr::release

unique_ptr::reset

unique_ptr::swap

Observers

unique_ptr::get

unique_ptr::get_deleter

unique_ptr::operator bool

unique_ptr::operator* unique_ptr::operator->

unique_ptr::operator[]

Non-member functions

operator== operator!= operator< operator> operator<= operator> operator>=

std::swap

std::hash

 

Defined in header <memory>
template<     class T,     class Deleter = std::default_delete<T> > class unique_ptr;	(1)	(since C++11)
template <     class T,     class Deleter > class unique_ptr<T[],Deleter>;	(2)	(since C++11)

std::unique_ptr is a smart pointer that:

• retains sole ownership of an object through a pointer, and
• destroys the pointed-to object when the unique_ptr goes out of scope.

unique_ptr is not copyable or copy-assignable, two instances of unique_ptr cannot manage the same object. A non-const unique_ptr can transfer the ownership of the managed object to another unique_ptr. A const std::unique_ptr cannot be transferred, limiting the lifetime of the managed object to the scope in which the pointer was created. When the unique_ptr is destroyed, it disposes of the object through Deleter.

There are two versions of std::unique_ptr:

1) manages the lifetime of a single object, e.g. allocated with new

2) manages the lifetime of an array with a runtime length, e.g. allocated with new[]

Typical uses of std::unique_ptr include

• providing exception safety to classes and functions that handle objects with dynamic lifetime, by guaranteeing deletion on both normal exit and exit through exception.

• passing ownership of uniquely-owned objects with dynamic lifetime into functions

• acquiring ownership of uniquely-owned objects with dynamic lifetime from functions

• as the element type in move-aware containers, such as std::vector, which hold pointers to dynamically-allocated objects, e.g. if polymorphic behavior is desired

Member types

Member type	Definition
pointer	std::remove_reference<D>::type::pointer if that type exists, otherwise T*
element_type	T, the type of the object managed by this unique_ptr
deleter_type	Deleter, the function object or lvalue reference to function or to function object, to be called from the destructor

Member functions

(constructor)	constructs a new unique_ptr (public member function)
(destructor)	destructs the managed object if such is present (public member function)
operator=	assigns the unique_ptr (public member function)
Modifiers
release	returns a pointer to the managed object and releases the ownership (public member function)
reset	replaces the managed object (public member function)
swap	swaps the managed objects (public member function)
Observers
get	returns a pointer to the managed object (public member function)
get_deleter	returns the deleter that is used for destruction of the managed object (public member function)
operator bool	checks if there is associated managed object (public member function)
Single-object version, unique_ptr<T>
operator* operator->	dereferences pointer to the managed object (public member function)
Array version, unique_ptr<T[]>
operator[]	provides indexed access to the managed array (public member function)

Non-member functions

operator== operator!= operator< operator<= operator> operator>=	compares to another unique_ptr or with nullptr (function template)
std::swap(std::unique_ptr) (C++11)	specializes the std::swap algorithm (function template)

Helper classes

std::hash<std::unique_ptr> (C++11)	hash support for std::unique_ptr (class template specialization)

Example

#include <iostream>
#include <memory>
 
struct Foo {
    Foo() { std::cout << "Foo::Foo\n"; }
    ~Foo() { std::cout << "Foo::~Foo\n"; }
    void bar() { std::cout << "Foo::bar\n"; }
};
 
void f(const Foo &foo)
{
    std::cout << "f(const Foo&)\n";
}
 
int main()
{
    std::unique_ptr<Foo> p1(new Foo);  // p1 owns Foo
    if (p1) p1->bar();
 
    {
        std::unique_ptr<Foo> p2(std::move(p1));  // now p2 owns Foo
        f(*p2);
 
        p1 = std::move(p2);  // ownership returns to p1
        std::cout << "destroying p2...\n";
    }
 
    if (p1) p1->bar();
 
    // Foo instance is destroyed when p1 goes out of scope
}

Output:

Foo::Foo
Foo::bar
f(const Foo&)
destroying p2...
Foo::bar
Foo::~Foo