NAME¶

std::experimental::shared_ptr::shared_ptr - std::experimental::shared_ptr::shared_ptr

Synopsis¶

constexpr shared_ptr() noexcept; (1)
constexpr shared_ptr( std::nullptr_t ) noexcept; (2)
template< class Y > (3)
explicit shared_ptr( Y* ptr );
template< class Y, class Deleter > (4)
shared_ptr( Y* ptr, Deleter d );
template< class Deleter > (5)
shared_ptr( std::nullptr_t ptr, Deleter d );
template< class Y, class Deleter, class Alloc > (6)
shared_ptr( Y* ptr, Deleter d, Alloc alloc );
template< class Deleter, class Alloc > (7)
shared_ptr( std::nullptr_t ptr, Deleter d, Alloc alloc );
template< class Y > (8)
shared_ptr( const shared_ptr<Y>& r, element_type *ptr ) noexcept;
shared_ptr( const shared_ptr& r ) noexcept; (9)
template< class Y > (9)
shared_ptr( const shared_ptr<Y>& r ) noexcept;
shared_ptr( shared_ptr&& r ) noexcept; (10)
template< class Y > (10)
shared_ptr( shared_ptr<Y>&& r ) noexcept;
template< class Y > (11)
explicit shared_ptr( const std::weak_ptr<Y>& r );
template< class Y > (12)
shared_ptr( std::auto_ptr<Y>&& r );
template< class Y, class Deleter > (13)
shared_ptr( std::unique_ptr<Y,Deleter>&& r );

Constructs new shared_ptr from a variety of pointer types that refer to an object to
manage.

For the purposes of the description below, a pointer type Y* is said to be
compatible with a pointer type T* if either Y* is convertible to T* or Y is the
array type U[N] and T is U cv [] (where cv is some set of cv-qualifiers).

1-2) Constructs a shared_ptr with no managed object, i.e. empty shared_ptr
3-7) Constructs a shared_ptr with ptr as the pointer to the managed object. If T is
an array type U[N], Y(*)[N] must be convertible to T*. If T is an array type U[],
Y(*)[] must be convertible to T*. Otherwise, Y* must be convertible to T*.
Additionally:
3) Uses a delete-expression (delete ptr, if T is not an array type; delete[] ptr if
T is an array type) as the deleter. Y must be a complete type. That delete
expression must be well formed, have well-defined behavior and not throw any
exceptions.
4-5) Uses the specified deleter d as the deleter. The expression 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.
6-7) Same as (4-5), but additionally uses a copy of alloc for allocation of data for
internal use. Alloc must be a Allocator, and its copy constructor and destructor
must not throw exceptions.
8) The aliasing constructor: constructs a shared_ptr which shares ownership
information with r, but holds an unrelated and unmanaged pointer ptr. Even if this
shared_ptr is the last of the group to go out of scope, it will call the destructor
for the object originally managed by r. However, calling get() on this will always
return a copy of ptr. It is the responsibility of the programmer to make sure that
this ptr remains valid as long as this shared_ptr exists, such as in the typical use
cases where ptr is a member of the object managed by r or is an alias (e.g.,
downcast) of r.get()
9) Constructs a shared_ptr which shares ownership of the object managed by r. If r
manages no object, *this manages no object too. The template overload doesn't
participate in overload resolution if Y* is not compatible with T*.
10) Move-constructs a shared_ptr from r. After the construction, *this contains a
copy of the previous state of r, r is empty. The template overload doesn't
participate in overload resolution if Y* is not compatible with T*.
11) Constructs a shared_ptr which shares ownership of the object managed by r. Y*
must be compatible with T*. Note that r.lock() may be used for the same purpose: the
difference is that this constructor throws an exception if the argument is empty,
while weak_ptr<T>::lock() constructs an empty shared_ptr in that case.
12) Constructs a shared_ptr that stores and owns the object formerly owned by r. Y*
must be convertible to T*. After construction, r is empty.
13) Constructs a shared_ptr which manages the object currently managed by r. The
deleter associated with r is stored for future deletion of the managed object. r
manages no object after the call. This overload doesn't participate in overload
resolution if Y* is not compatible with T*.
If D is a reference type, equivalent to shared_ptr(r.release(),
std::ref(r.get_deleter()). Otherwise, equivalent to shared_ptr(r.release(),
r.get_deleter())

Notes¶

When constructing a shared_ptr from a raw pointer to an object of a type derived
from std::experimental::enable_shared_from_this, the constructors of shared_ptr
update the private weak_ptr member of the std::experimental::enable_shared_from_this
base so that future calls to shared_from_this() would share ownership with the
shared_ptr created by this raw pointer constructor.

The raw pointer overloads assume ownership of the pointed-to object, and so
constructing a shared_ptr using the raw pointer overload for an object that is
already managed by a shared_ptr may lead to undefined behavior, even if the object
is of a type derived from std::experimental::enable_shared_from_this.

Parameters¶

ptr - a pointer to an object to manage
d - a deleter to use to destroy the object
alloc - an allocator to use for allocations of data for internal use
r - another smart pointer to share the ownership to or acquire the ownership
from

Exceptions¶

3) std::bad_alloc if required additional memory could not be obtained. May throw
implementation-defined exception for other errors. The applicable delete-expression
(delete ptr if T is not an array type, delete[] ptr otherwise) is called if an
exception occurs.
4-7) 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.

11) std::bad_weak_ptr if r.expired() == true. The constructor has no effect in this
case.
12) std::bad_alloc if required additional memory could not be obtained. May throw
implementation-defined exception for other errors. This constructor has no effect if
an exception occurs.
13) If an exception is thrown, the constructor has no effects.

Example¶

This section is incomplete
Reason: no example

See also¶

make_shared creates a shared pointer that manages a new object
make_shared_for_overwrite (function template)
(C++20)
allocate_shared creates a shared pointer that manages a new object
allocate_shared_for_overwrite allocated using an allocator
(C++20) (function template)