std::shared_ptr - Man Page

A smart pointer with reference-counted copy semantics.

Synopsis

#include <memory>

Inherits std::__shared_ptr< _Tp, _Lp >.

Public Types

using element_type = typename __shared_ptr< _Tp >::element_type
The type pointed to by the stored pointer, remove_extent_t<_Tp>
using weak_type = weak_ptr< _Tp >
The corresponding weak_ptr type for this shared_ptr.

Public Member Functions

constexpr shared_ptr () noexcept
Construct an empty shared_ptr.
template<typename _Yp , typename  = _Constructible<_Yp*>> shared_ptr (_Yp *__p)
Construct a shared_ptr that owns the pointer __p.
template<typename _Yp , typename _Deleter , typename  = _Constructible<_Yp*, _Deleter>> shared_ptr (_Yp *__p, _Deleter __d)
Construct a shared_ptr that owns the pointer __p and the deleter __d.
template<typename _Yp , typename _Deleter , typename _Alloc , typename  = _Constructible<_Yp*, _Deleter, _Alloc>> shared_ptr (_Yp *__p, _Deleter __d, _Alloc __a)
Construct a shared_ptr that owns the pointer __p and the deleter __d.
template<typename _Yp , typename  = _Constructible<auto_ptr<_Yp>>> shared_ptr (auto_ptr< _Yp > &&__r)
shared_ptr (const shared_ptr &) noexcept=default
Copy constructor.
template<typename _Yp , typename  = _Constructible<const shared_ptr<_Yp>&>> shared_ptr (const shared_ptr< _Yp > &__r) noexcept
If __r is empty, constructs an empty shared_ptr; otherwise construct a shared_ptr that shares ownership with __r.
template<typename _Yp > shared_ptr (const shared_ptr< _Yp > &__r, element_type *__p) noexcept
Constructs a shared_ptr instance that stores __p and shares ownership with __r.
template<typename _Yp , typename  = _Constructible<const weak_ptr<_Yp>&>> shared_ptr (const weak_ptr< _Yp > &__r)
Constructs a shared_ptr that shares ownership with __r and stores a copy of the pointer stored in __r.
template<typename _Deleter > shared_ptr (nullptr_t __p, _Deleter __d)
Construct a shared_ptr that owns a null pointer and the deleter __d.
template<typename _Deleter , typename _Alloc > shared_ptr (nullptr_t __p, _Deleter __d, _Alloc __a)
Construct a shared_ptr that owns a null pointer and the deleter __d.
constexpr shared_ptr (nullptr_t) noexcept
Construct an empty shared_ptr.
shared_ptr (shared_ptr &&__r) noexcept
Move-constructs a shared_ptr instance from __r.
template<typename _Yp , typename  = _Constructible<shared_ptr<_Yp>>> shared_ptr (shared_ptr< _Yp > &&__r) noexcept
Move-constructs a shared_ptr instance from __r.
template<typename _Yp > shared_ptr (shared_ptr< _Yp > &&__r, element_type *__p) noexcept
Constructs a shared_ptr instance that stores __p and shares ownership with __r.
template<typename _Tp1 , typename > shared_ptr (std::auto_ptr< _Tp1 > &&__r)
template<typename _Yp , typename _Del , typename  = _Constructible<unique_ptr<_Yp, _Del>>> shared_ptr (unique_ptr< _Yp, _Del > &&__r)
element_type * get () const noexcept
Return the stored pointer.
operator bool () const noexcept
Return true if the stored pointer is not null.
element_type & operator* () const noexcept
element_type * operator-> () const noexcept
template<typename _Yp > _Assignable< auto_ptr< _Yp > > operator= (auto_ptr< _Yp > &&__r)
shared_ptr & operator= (const shared_ptr &) noexcept=default
template<typename _Yp > _Assignable< const shared_ptr< _Yp > & > operator= (const shared_ptr< _Yp > &__r) noexcept
shared_ptr & operator= (shared_ptr &&__r) noexcept
template<class _Yp > _Assignable< shared_ptr< _Yp > > operator= (shared_ptr< _Yp > &&__r) noexcept
template<typename _Yp , typename _Del > _Assignable< unique_ptr< _Yp, _Del > > operator= (unique_ptr< _Yp, _Del > &&__r)
void reset () noexcept
template<typename _Yp > _SafeConv< _Yp > reset (_Yp *__p)
template<typename _Yp , typename _Deleter > _SafeConv< _Yp > reset (_Yp *__p, _Deleter __d)
template<typename _Yp , typename _Deleter , typename _Alloc > _SafeConv< _Yp > reset (_Yp *__p, _Deleter __d, _Alloc __a)
void swap (__shared_ptr< _Tp, _Lp > &__other) noexcept
Exchange both the owned pointer and the stored pointer.
bool unique () const noexcept
Return true if use_count() == 1.
long use_count () const noexcept
If *this owns a pointer, return the number of owners, otherwise zero.

template<typename _Tp1 > bool owner_before (__shared_ptr< _Tp1, _Lp > const &__rhs) const noexcept
Define an ordering based on ownership.
template<typename _Tp1 > bool owner_before (__weak_ptr< _Tp1, _Lp > const &__rhs) const noexcept
Define an ordering based on ownership.

Friends

template<typename _Yp , typename _Alloc > shared_ptr< _BoundedArray< _Yp > > allocate_shared (const _Alloc &)
template<typename _Yp , typename _Alloc , typename... _Args> shared_ptr< _NonArray< _Yp > > allocate_shared (const _Alloc &, _Args &&...)
template<typename _Yp , typename _Alloc > shared_ptr< _BoundedArray< _Yp > > allocate_shared (const _Alloc &, const remove_extent_t< _Yp > &)
template<typename _Yp , typename _Alloc > shared_ptr< _UnboundedArray< _Yp > > allocate_shared (const _Alloc &, size_t)
template<typename _Yp , typename _Alloc > shared_ptr< _UnboundedArray< _Yp > > allocate_shared (const _Alloc &, size_t, const remove_extent_t< _Yp > &)
template<typename _Yp , typename _Alloc > shared_ptr< _NotUnboundedArray< _Yp > > allocate_shared_for_overwrite (const _Alloc &)
template<typename _Yp , typename _Alloc > shared_ptr< _UnboundedArray< _Yp > > allocate_shared_for_overwrite (const _Alloc &, size_t)
template<typename _Yp > shared_ptr< _BoundedArray< _Yp > > make_shared ()
template<typename _Yp , typename... _Args> shared_ptr< _NonArray< _Yp > > make_shared (_Args &&...)
template<typename _Yp > shared_ptr< _BoundedArray< _Yp > > make_shared (const remove_extent_t< _Yp > &)
template<typename _Yp > shared_ptr< _UnboundedArray< _Yp > > make_shared (size_t)
template<typename _Yp > shared_ptr< _UnboundedArray< _Yp > > make_shared (size_t, const remove_extent_t< _Yp > &)
template<typename _Yp > shared_ptr< _NotUnboundedArray< _Yp > > make_shared_for_overwrite ()
template<typename _Yp > shared_ptr< _UnboundedArray< _Yp > > make_shared_for_overwrite (size_t)
class weak_ptr< _Tp >

Detailed Description

template<typename _Tp>

class std::shared_ptr< _Tp >"A smart pointer with reference-counted copy semantics.

Since

C++11

A shared_ptr object is either empty or owns a pointer passed to the constructor. Copies of a shared_ptr share ownership of the same pointer. When the last shared_ptr that owns the pointer is destroyed or reset, the owned pointer is freed (either by delete or by invoking a custom deleter that was passed to the constructor).

A shared_ptr also stores another pointer, which is usually (but not always) the same pointer as it owns. The stored pointer can be retrieved by calling the get() member function.

The equality and relational operators for shared_ptr only compare the stored pointer returned by get(), not the owned pointer. To test whether two shared_ptr objects share ownership of the same pointer see std::shared_ptr::owner_before and std::owner_less.

Definition at line 175 of file bits/shared_ptr.h.

Member Typedef Documentation

template<typename _Tp > using std::shared_ptr< _Tp >::element_type =  typename __shared_ptr<_Tp>::element_type

The type pointed to by the stored pointer, remove_extent_t<_Tp>

Definition at line 190 of file bits/shared_ptr.h.

template<typename _Tp > using std::shared_ptr< _Tp >::weak_type =  weak_ptr<_Tp>

The corresponding weak_ptr type for this shared_ptr.

Since

C++17

Definition at line 196 of file bits/shared_ptr.h.

Constructor & Destructor Documentation

template<typename _Tp > constexpr std::shared_ptr< _Tp >::shared_ptr () [inline], [constexpr], [noexcept]

Construct an empty shared_ptr.

Postcondition

use_count()==0 && get()==0

Definition at line 202 of file bits/shared_ptr.h.

template<typename _Tp > std::shared_ptr< _Tp >::shared_ptr (const shared_ptr< _Tp > &) [default], [noexcept]

Copy constructor.

template<typename _Tp > template<typename _Yp , typename  = _Constructible<_Yp*>> std::shared_ptr< _Tp >::shared_ptr (_Yp * __p) [inline], [explicit]

Construct a shared_ptr that owns the pointer __p.

Parameters

__p A pointer that is convertible to element_type*.

Postcondition

use_count() == 1 && get() == __p

Exceptions

std::bad_alloc,in which case delete __p is called.

Definition at line 214 of file bits/shared_ptr.h.

template<typename _Tp > template<typename _Yp , typename _Deleter , typename  = _Constructible<_Yp*, _Deleter>> std::shared_ptr< _Tp >::shared_ptr (_Yp * __p, _Deleter __d) [inline]

Construct a shared_ptr that owns the pointer __p and the deleter __d.

Parameters

__p A pointer.
__d A deleter.

Postcondition

use_count() == 1 && get() == __p

Exceptions

std::bad_alloc,in which case __d(__p) is called.

Requirements: _Deleter's copy constructor and destructor must not throw

__shared_ptr will release __p by calling __d(__p)

Definition at line 231 of file bits/shared_ptr.h.

template<typename _Tp > template<typename _Deleter > std::shared_ptr< _Tp >::shared_ptr (nullptr_t __p, _Deleter __d) [inline]

Construct a shared_ptr that owns a null pointer and the deleter __d.

Parameters

__p A null pointer constant.
__d A deleter.

Postcondition

use_count() == 1 && get() == __p

Exceptions

std::bad_alloc,in which case __d(__p) is called.

Requirements: _Deleter's copy constructor and destructor must not throw

The last owner will call __d(__p)

Definition at line 248 of file bits/shared_ptr.h.

template<typename _Tp > template<typename _Yp , typename _Deleter , typename _Alloc , typename  = _Constructible<_Yp*, _Deleter, _Alloc>> std::shared_ptr< _Tp >::shared_ptr (_Yp * __p, _Deleter __d, _Alloc __a) [inline]

Construct a shared_ptr that owns the pointer __p and the deleter __d.

Parameters

__p A pointer.
__d A deleter.
__a An allocator.

Postcondition

use_count() == 1 && get() == __p

Exceptions

std::bad_alloc,in which case __d(__p) is called.

Requirements: _Deleter's copy constructor and destructor must not throw _Alloc's copy constructor and destructor must not throw.

__shared_ptr will release __p by calling __d(__p)

Definition at line 268 of file bits/shared_ptr.h.

template<typename _Tp > template<typename _Deleter , typename _Alloc > std::shared_ptr< _Tp >::shared_ptr (nullptr_t __p, _Deleter __d, _Alloc __a) [inline]

Construct a shared_ptr that owns a null pointer and the deleter __d.

Parameters

__p A null pointer constant.
__d A deleter.
__a An allocator.

Postcondition

use_count() == 1 && get() == __p

Exceptions

std::bad_alloc,in which case __d(__p) is called.

Requirements: _Deleter's copy constructor and destructor must not throw _Alloc's copy constructor and destructor must not throw.

The last owner will call __d(__p)

Definition at line 287 of file bits/shared_ptr.h.

template<typename _Tp > template<typename _Yp > std::shared_ptr< _Tp >::shared_ptr (const shared_ptr< _Yp > & __r, element_type * __p) [inline], [noexcept]

Constructs a shared_ptr instance that stores __p and shares ownership with __r.

Parameters

__r A shared_ptr.
__p A pointer that will remain valid while *__r is valid.

Postcondition

get() == __p && use_count() == __r.use_count()

This can be used to construct a shared_ptr to a sub-object of an object managed by an existing shared_ptr. The complete object will remain valid while any shared_ptr owns it, even if they don't store a pointer to the complete object.

shared_ptr<pair<int,int>> pii(new pair<int,int>());
shared_ptr<int> pi(pii, &pii->first);
assert(pii.use_count() == 2);

Definition at line 311 of file bits/shared_ptr.h.

template<typename _Tp > template<typename _Yp > std::shared_ptr< _Tp >::shared_ptr (shared_ptr< _Yp > && __r, element_type * __p) [inline], [noexcept]

Constructs a shared_ptr instance that stores __p and shares ownership with __r.

Parameters

__r A shared_ptr.
__p A pointer that will remain valid while *__r is valid.

Postcondition

get() == __p && !__r.use_count() && !__r.get()

Since

C++17

This can be used to construct a shared_ptr to a sub-object of an object managed by an existing shared_ptr. The complete object will remain valid while any shared_ptr owns it, even if they don't store a pointer to the complete object.

shared_ptr<pair<int,int>> pii(new pair<int,int>());
shared_ptr<int> pi1(pii, &pii->first);
assert(pii.use_count() == 2);
shared_ptr<int> pi2(std::move(pii), &pii->second);
assert(pii.use_count() == 0);

Definition at line 339 of file bits/shared_ptr.h.

template<typename _Tp > template<typename _Yp , typename  = _Constructible<const shared_ptr<_Yp>&>> std::shared_ptr< _Tp >::shared_ptr (const shared_ptr< _Yp > & __r) [inline], [noexcept]

If __r is empty, constructs an empty shared_ptr; otherwise construct a shared_ptr that shares ownership with __r.

Parameters

__r A shared_ptr.

Postcondition

get() == __r.get() && use_count() == __r.use_count()

Definition at line 351 of file bits/shared_ptr.h.

template<typename _Tp > std::shared_ptr< _Tp >::shared_ptr (shared_ptr< _Tp > && __r) [inline], [noexcept]

Move-constructs a shared_ptr instance from __r.

Parameters

__r A shared_ptr rvalue.

Postcondition

*this contains the old value of __r, __r is empty.

Definition at line 359 of file bits/shared_ptr.h.

template<typename _Tp > template<typename _Yp , typename  = _Constructible<shared_ptr<_Yp>>> std::shared_ptr< _Tp >::shared_ptr (shared_ptr< _Yp > && __r) [inline], [noexcept]

Move-constructs a shared_ptr instance from __r.

Parameters

__r A shared_ptr rvalue.

Postcondition

*this contains the old value of __r, __r is empty.

Definition at line 368 of file bits/shared_ptr.h.

template<typename _Tp > template<typename _Yp , typename  = _Constructible<const weak_ptr<_Yp>&>> std::shared_ptr< _Tp >::shared_ptr (const weak_ptr< _Yp > & __r) [inline], [explicit]

Constructs a shared_ptr that shares ownership with __r and stores a copy of the pointer stored in __r.

Parameters

__r A weak_ptr.

Postcondition

use_count() == __r.use_count()

Exceptions

bad_weak_ptr when __r.expired(), in which case the constructor has no effect.

Definition at line 380 of file bits/shared_ptr.h.

template<typename _Tp > template<typename _Yp , typename _Del , typename  = _Constructible<unique_ptr<_Yp, _Del>>> std::shared_ptr< _Tp >::shared_ptr (unique_ptr< _Yp, _Del > && __r) [inline]

Definition at line 395 of file bits/shared_ptr.h.

template<typename _Tp > constexpr std::shared_ptr< _Tp >::shared_ptr (nullptr_t) [inline], [constexpr], [noexcept]

Construct an empty shared_ptr.

Postcondition

use_count() == 0 && get() == nullptr

Definition at line 412 of file bits/shared_ptr.h.

template<typename _Tp > template<typename _Tp1 , typename > std::shared_ptr< _Tp >::shared_ptr (std::auto_ptr< _Tp1 > && __r) [inline]

Definition at line 322 of file auto_ptr.h.

Member Function Documentation

template<typename _Tp , _Lock_policy _Lp> element_type * std::__shared_ptr< _Tp, _Lp >::get () const [inline], [noexcept], [inherited]

Return the stored pointer.

Definition at line 1665 of file shared_ptr_base.h.

template<typename _Tp , _Lock_policy _Lp> std::__shared_ptr< _Tp, _Lp >::operator bool () const [inline], [explicit], [noexcept], [inherited]

Return true if the stored pointer is not null.

Definition at line 1669 of file shared_ptr_base.h.

template<typename _Tp , _Lock_policy _Lp, bool  = is_array<_Tp>::value, bool  = is_void<_Tp>::value> element_type & std::__shared_ptr_access< _Tp, _Lp, bool, bool >::operator* () const [inline], [noexcept], [inherited]

Definition at line 1347 of file shared_ptr_base.h.

template<typename _Tp , _Lock_policy _Lp, bool  = is_array<_Tp>::value, bool  = is_void<_Tp>::value> element_type * std::__shared_ptr_access< _Tp, _Lp, bool, bool >::operator-> () const [inline], [noexcept], [inherited]

Definition at line 1354 of file shared_ptr_base.h.

template<typename _Tp > template<typename _Yp > _Assignable< auto_ptr< _Yp > > std::shared_ptr< _Tp >::operator= (auto_ptr< _Yp > && __r) [inline]

Definition at line 429 of file bits/shared_ptr.h.

template<typename _Tp > template<typename _Yp > _Assignable< const shared_ptr< _Yp > & > std::shared_ptr< _Tp >::operator= (const shared_ptr< _Yp > & __r) [inline], [noexcept]

Definition at line 418 of file bits/shared_ptr.h.

template<typename _Tp > shared_ptr & std::shared_ptr< _Tp >::operator= (shared_ptr< _Tp > && __r) [inline], [noexcept]

Definition at line 438 of file bits/shared_ptr.h.

template<typename _Tp > template<class _Yp > _Assignable< shared_ptr< _Yp > > std::shared_ptr< _Tp >::operator= (shared_ptr< _Yp > && __r) [inline], [noexcept]

Definition at line 446 of file bits/shared_ptr.h.

template<typename _Tp > template<typename _Yp , typename _Del > _Assignable< unique_ptr< _Yp, _Del > > std::shared_ptr< _Tp >::operator= (unique_ptr< _Yp, _Del > && __r) [inline]

Definition at line 454 of file bits/shared_ptr.h.

template<typename _Tp , _Lock_policy _Lp> template<typename _Tp1 > bool std::__shared_ptr< _Tp, _Lp >::owner_before (__shared_ptr< _Tp1, _Lp > const & __rhs) const [inline], [noexcept], [inherited]

Define an ordering based on ownership. This function defines a strict weak ordering between two shared_ptr or weak_ptr objects, such that one object is less than the other unless they share ownership of the same pointer, or are both empty.

Definition at line 1699 of file shared_ptr_base.h.

template<typename _Tp , _Lock_policy _Lp> template<typename _Tp1 > bool std::__shared_ptr< _Tp, _Lp >::owner_before (__weak_ptr< _Tp1, _Lp > const & __rhs) const [inline], [noexcept], [inherited]

Define an ordering based on ownership. This function defines a strict weak ordering between two shared_ptr or weak_ptr objects, such that one object is less than the other unless they share ownership of the same pointer, or are both empty.

Definition at line 1704 of file shared_ptr_base.h.

template<typename _Tp , _Lock_policy _Lp> void std::__shared_ptr< _Tp, _Lp >::reset () [inline], [noexcept], [inherited]

Definition at line 1641 of file shared_ptr_base.h.

template<typename _Tp , _Lock_policy _Lp> template<typename _Yp > _SafeConv< _Yp > std::__shared_ptr< _Tp, _Lp >::reset (_Yp * __p) [inline], [inherited]

Definition at line 1646 of file shared_ptr_base.h.

template<typename _Tp , _Lock_policy _Lp> template<typename _Yp , typename _Deleter > _SafeConv< _Yp > std::__shared_ptr< _Tp, _Lp >::reset (_Yp * __p, _Deleter __d) [inline], [inherited]

Definition at line 1655 of file shared_ptr_base.h.

template<typename _Tp , _Lock_policy _Lp> template<typename _Yp , typename _Deleter , typename _Alloc > _SafeConv< _Yp > std::__shared_ptr< _Tp, _Lp >::reset (_Yp * __p, _Deleter __d, _Alloc __a) [inline], [inherited]

Definition at line 1660 of file shared_ptr_base.h.

template<typename _Tp , _Lock_policy _Lp> void std::__shared_ptr< _Tp, _Lp >::swap (__shared_ptr< _Tp, _Lp > & __other) [inline], [noexcept], [inherited]

Exchange both the owned pointer and the stored pointer.

Definition at line 1684 of file shared_ptr_base.h.

template<typename _Tp , _Lock_policy _Lp> bool std::__shared_ptr< _Tp, _Lp >::unique () const [inline], [noexcept], [inherited]

Return true if use_count() == 1.

Definition at line 1674 of file shared_ptr_base.h.

template<typename _Tp , _Lock_policy _Lp> long std::__shared_ptr< _Tp, _Lp >::use_count () const [inline], [noexcept], [inherited]

If *this owns a pointer, return the number of owners, otherwise zero.

Definition at line 1679 of file shared_ptr_base.h.

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