20 General utilities library [utilities]

20.11 Smart pointers [smartptr]

20.11.1 Class template unique_­ptr [unique.ptr]

20.11.1.1 General [unique.ptr.general]

1
#
A unique pointer is an object that owns another object and manages that other object through a pointer.
More precisely, a unique pointer is an object u that stores a pointer to a second object p and will dispose of p when u is itself destroyed (e.g., when leaving block scope ([stmt.dcl])).
In this context, u is said to own p.
2
#
The mechanism by which u disposes of p is known as p's associated deleter, a function object whose correct invocation results in p's appropriate disposition (typically its deletion).
3
#
Let the notation u.p denote the pointer stored by u, and let u.d denote the associated deleter.
Upon request, u can reset (replace) u.p and u.d with another pointer and deleter, but properly disposes of its owned object via the associated deleter before such replacement is considered completed.
4
#
Each object of a type U instantiated from the unique_­ptr template specified in [unique.ptr] has the strict ownership semantics, specified above, of a unique pointer.
In partial satisfaction of these semantics, each such U is Cpp17MoveConstructible and Cpp17MoveAssignable, but is not Cpp17CopyConstructible nor Cpp17CopyAssignable.
The template parameter T of unique_­ptr may be an incomplete type.
5
#
[Note 1:
The uses of unique_­ptr include providing exception safety for dynamically allocated memory, passing ownership of dynamically allocated memory to a function, and returning dynamically allocated memory from a function.
— end note]

20.11.1.2 Default deleters [unique.ptr.dltr]

20.11.1.2.1 In general [unique.ptr.dltr.general]

1
#
The class template default_­delete serves as the default deleter (destruction policy) for the class template unique_­ptr.
2
#
The template parameter T of default_­delete may be an incomplete type.

20.11.1.2.2 default_­delete [unique.ptr.dltr.dflt]

namespace std { template<class T> struct default_delete { constexpr default_delete() noexcept = default; template<class U> default_delete(const default_delete<U>&) noexcept; void operator()(T*) const; }; }
🔗
template<class U> default_delete(const default_delete<U>& other) noexcept;
1
#
Constraints: U* is implicitly convertible to T*.
2
#
Effects: Constructs a default_­delete object from another default_­delete<U> object.
🔗
void operator()(T* ptr) const;
3
#
Mandates: T is a complete type.
4
#
Effects: Calls delete on ptr.

20.11.1.2.3 default_­delete<T[]> [unique.ptr.dltr.dflt1]

namespace std { template<class T> struct default_delete<T[]> { constexpr default_delete() noexcept = default; template<class U> default_delete(const default_delete<U[]>&) noexcept; template<class U> void operator()(U* ptr) const; }; }
🔗
template<class U> default_delete(const default_delete<U[]>& other) noexcept;
1
#
Constraints: U(*)[] is convertible to T(*)[].
2
#
Effects: Constructs a default_­delete object from another default_­delete<U[]> object.
🔗
template<class U> void operator()(U* ptr) const;
3
#
Constraints: U(*)[] is convertible to T(*)[].
4
#
Mandates: U is a complete type.
5
#
Effects: Calls delete[] on ptr.

20.11.1.3 unique_­ptr for single objects [unique.ptr.single]

20.11.1.3.1 General [unique.ptr.single.general]

namespace std { template<class T, class D = default_delete<T>> class unique_ptr { public: using pointer = see below; using element_type = T; using deleter_type = D; // [unique.ptr.single.ctor], constructors constexpr unique_ptr() noexcept; explicit unique_ptr(pointer p) noexcept; unique_ptr(pointer p, see below d1) noexcept; unique_ptr(pointer p, see below d2) noexcept; unique_ptr(unique_ptr&& u) noexcept; constexpr unique_ptr(nullptr_t) noexcept; template<class U, class E> unique_ptr(unique_ptr<U, E>&& u) noexcept; // [unique.ptr.single.dtor], destructor ~unique_ptr(); // [unique.ptr.single.asgn], assignment unique_ptr& operator=(unique_ptr&& u) noexcept; template<class U, class E> unique_ptr& operator=(unique_ptr<U, E>&& u) noexcept; unique_ptr& operator=(nullptr_t) noexcept; // [unique.ptr.single.observers], observers add_lvalue_reference_t<T> operator*() const; pointer operator->() const noexcept; pointer get() const noexcept; deleter_type& get_deleter() noexcept; const deleter_type& get_deleter() const noexcept; explicit operator bool() const noexcept; // [unique.ptr.single.modifiers], modifiers pointer release() noexcept; void reset(pointer p = pointer()) noexcept; void swap(unique_ptr& u) noexcept; // disable copy from lvalue unique_ptr(const unique_ptr&) = delete; unique_ptr& operator=(const unique_ptr&) = delete; }; }
1
#
The default type for the template parameter D is default_­delete.
A client-supplied template argument D shall be a function object type, lvalue reference to function, or lvalue reference to function object type for which, given a value d of type D and a value ptr of type unique_­ptr<T, D>​::​pointer, the expression d(ptr) is valid and has the effect of disposing of the pointer as appropriate for that deleter.
2
#
If the deleter's type D is not a reference type, D shall meet the Cpp17Destructible requirements (Table 32).
3
#
If the qualified-id remove_­reference_­t<D>​::​pointer is valid and denotes a type ([temp.deduct]), then unique_­ptr<T, D>​::​pointer shall be a synonym for remove_­reference_­t<D>​::​pointer.
Otherwise unique_­ptr<T, D>​::​pointer shall be a synonym for element_­type*.
The type unique_­ptr<T, D>​::​pointer shall meet the Cpp17NullablePointer requirements (Table 33).
4
#
[Example 1:
Given an allocator type X (Table 36) and letting A be a synonym for allocator_­traits<X>, the types A​::​pointer, A​::​const_­pointer, A​::​void_­pointer, and A​::​const_­void_­pointer may be used as unique_­ptr<T, D>​::​pointer.
— end example]

20.11.1.3.2 Constructors [unique.ptr.single.ctor]

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constexpr unique_ptr() noexcept; constexpr unique_ptr(nullptr_t) noexcept;
1
#
Constraints: is_­pointer_­v<deleter_­type> is false and is_­default_­constructible_­v<deleter_­type> is true.
2
#
Preconditions: D meets the Cpp17DefaultConstructible requirements (Table 27), and that construction does not throw an exception.
3
#
Effects: Constructs a unique_­ptr object that owns nothing, value-initializing the stored pointer and the stored deleter.
4
#
Postconditions: get() == nullptr.
get_­deleter() returns a reference to the stored deleter.
🔗
explicit unique_ptr(pointer p) noexcept;
5
#
Constraints: is_­pointer_­v<deleter_­type> is false and is_­default_­constructible_­v<deleter_­type> is true.
6
#
Mandates: This constructor is not selected by class template argument deduction ([over.match.class.deduct]).
7
#
Preconditions: D meets the Cpp17DefaultConstructible requirements (Table 27), and that construction does not throw an exception.
8
#
Effects: Constructs a unique_­ptr which owns p, initializing the stored pointer with p and value-initializing the stored deleter.
9
#
Postconditions: get() == p.
get_­deleter() returns a reference to the stored deleter.
🔗
unique_ptr(pointer p, const D& d) noexcept; unique_ptr(pointer p, remove_reference_t<D>&& d) noexcept;
10
#
Constraints: is_­constructible_­v<D, decltype(d)> is true.
11
#
Mandates: These constructors are not selected by class template argument deduction ([over.match.class.deduct]).
12
#
Preconditions: For the first constructor, if D is not a reference type, D meets the Cpp17CopyConstructible requirements and such construction does not exit via an exception.
For the second constructor, if D is not a reference type, D meets the Cpp17MoveConstructible requirements and such construction does not exit via an exception.
13
#
Effects: Constructs a unique_­ptr object which owns p, initializing the stored pointer with p and initializing the deleter from std​::​forward<decltype(d)>(d).
14
#
Postconditions: get() == p.
get_­deleter() returns a reference to the stored deleter.
If D is a reference type then get_­deleter() returns a reference to the lvalue d.
15
#
Remarks: If D is a reference type, the second constructor is defined as deleted.
16
#
[Example 1: D d; unique_ptr<int, D> p1(new int, D()); // D must be Cpp17MoveConstructible unique_ptr<int, D> p2(new int, d); // D must be Cpp17CopyConstructible unique_ptr<int, D&> p3(new int, d); // p3 holds a reference to d unique_ptr<int, const D&> p4(new int, D()); // error: rvalue deleter object combined // with reference deleter type — end example]
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unique_ptr(unique_ptr&& u) noexcept;
17
#
Constraints: is_­move_­constructible_­v<D> is true.
18
#
Preconditions: If D is not a reference type, D meets the Cpp17MoveConstructible requirements (Table 28).
Construction of the deleter from an rvalue of type D does not throw an exception.
19
#
Effects: Constructs a unique_­ptr from u.
If D is a reference type, this deleter is copy constructed from u's deleter; otherwise, this deleter is move constructed from u's deleter.
[Note 1:
The construction of the deleter can be implemented with std​::​forward<D>.
— end note]
20
#
Postconditions: get() yields the value u.get() yielded before the construction.
u.get() == nullptr.
get_­deleter() returns a reference to the stored deleter that was constructed from u.get_­deleter().
If D is a reference type then get_­deleter() and u.get_­deleter() both reference the same lvalue deleter.
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template<class U, class E> unique_ptr(unique_ptr<U, E>&& u) noexcept;
21
#
Constraints:
  • (21.1)
    unique_­ptr<U, E>​::​pointer is implicitly convertible to pointer,
  • (21.2)
    U is not an array type, and
  • (21.3)
    either D is a reference type and E is the same type as D, or D is not a reference type and E is implicitly convertible to D.
22
#
Preconditions: If E is not a reference type, construction of the deleter from an rvalue of type E is well-formed and does not throw an exception.
Otherwise, E is a reference type and construction of the deleter from an lvalue of type E is well-formed and does not throw an exception.
23
#
Effects: Constructs a unique_­ptr from u.
If E is a reference type, this deleter is copy constructed from u's deleter; otherwise, this deleter is move constructed from u's deleter.
[Note 2:
The deleter constructor can be implemented with std​::​forward<E>.
— end note]
24
#
Postconditions: get() yields the value u.get() yielded before the construction.
u.get() == nullptr.
get_­deleter() returns a reference to the stored deleter that was constructed from u.get_­deleter().

20.11.1.3.3 Destructor [unique.ptr.single.dtor]

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~unique_ptr();
1
#
Preconditions: The expression get_­deleter()(get()) is well-formed, has well-defined behavior, and does not throw exceptions.
[Note 1:
The use of default_­delete requires T to be a complete type.
— end note]
2
#
Effects: If get() == nullptr there are no effects.
Otherwise get_­deleter()(get()).

20.11.1.3.4 Assignment [unique.ptr.single.asgn]

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unique_ptr& operator=(unique_ptr&& u) noexcept;
1
#
Constraints: is_­move_­assignable_­v<D> is true.
2
#
Preconditions: If D is not a reference type, D meets the Cpp17MoveAssignable requirements (Table 30) and assignment of the deleter from an rvalue of type D does not throw an exception.
Otherwise, D is a reference type; remove_­reference_­t<D> meets the Cpp17CopyAssignable requirements and assignment of the deleter from an lvalue of type D does not throw an exception.
3
#
Effects: Calls reset(u.release()) followed by get_­deleter() = std​::​forward<D>(u.get_­deleter()).
4
#
Postconditions: u.get() == nullptr.
5
#
Returns: *this.
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template<class U, class E> unique_ptr& operator=(unique_ptr<U, E>&& u) noexcept;
6
#
Constraints:
  • (6.1)
    unique_­ptr<U, E>​::​pointer is implicitly convertible to pointer, and
  • (6.2)
    U is not an array type, and
  • (6.3)
    is_­assignable_­v<D&, E&&> is true.
7
#
Preconditions: If E is not a reference type, assignment of the deleter from an rvalue of type E is well-formed and does not throw an exception.
Otherwise, E is a reference type and assignment of the deleter from an lvalue of type E is well-formed and does not throw an exception.
8
#
Effects: Calls reset(u.release()) followed by get_­deleter() = std​::​forward<E>(u.get_­deleter()).
9
#
Postconditions: u.get() == nullptr.
10
#
Returns: *this.
🔗
unique_ptr& operator=(nullptr_t) noexcept;
11
#
Effects: As if by reset().
12
#
Postconditions: get() == nullptr.
13
#
Returns: *this.

20.11.1.3.5 Observers [unique.ptr.single.observers]

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add_lvalue_reference_t<T> operator*() const;
1
#
Preconditions: get() != nullptr.
2
#
Returns: *get().
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pointer operator->() const noexcept;
3
#
Preconditions: get() != nullptr.
4
#
Returns: get().
5
#
[Note 1:
The use of this function typically requires that T be a complete type.
— end note]
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pointer get() const noexcept;
6
#
Returns: The stored pointer.
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deleter_type& get_deleter() noexcept; const deleter_type& get_deleter() const noexcept;
7
#
Returns: A reference to the stored deleter.
🔗
explicit operator bool() const noexcept;
8
#
Returns: get() != nullptr.

20.11.1.3.6 Modifiers [unique.ptr.single.modifiers]

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pointer release() noexcept;
1
#
Postconditions: get() == nullptr.
2
#
Returns: The value get() had at the start of the call to release.
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void reset(pointer p = pointer()) noexcept;
3
#
Preconditions: The expression get_­deleter()(get()) is well-formed, has well-defined behavior, and does not throw exceptions.
4
#
Effects: Assigns p to the stored pointer, and then if and only if the old value of the stored pointer, old_­p, was not equal to nullptr, calls get_­deleter()(old_­p).
[Note 1:
The order of these operations is significant because the call to get_­deleter() might destroy *this.
— end note]
5
#
Postconditions: get() == p.
[Note 2:
The postcondition does not hold if the call to get_­deleter() destroys *this since this->get() is no longer a valid expression.
— end note]
🔗
void swap(unique_ptr& u) noexcept;
6
#
Preconditions: get_­deleter() is swappable ([swappable.requirements]) and does not throw an exception under swap.
7
#
Effects: Invokes swap on the stored pointers and on the stored deleters of *this and u.

20.11.1.4 unique_­ptr for array objects with a runtime length [unique.ptr.runtime]

20.11.1.4.1 General [unique.ptr.runtime.general]

namespace std { template<class T, class D> class unique_ptr<T[], D> { public: using pointer = see below; using element_type = T; using deleter_type = D; // [unique.ptr.runtime.ctor], constructors constexpr unique_ptr() noexcept; template<class U> explicit unique_ptr(U p) noexcept; template<class U> unique_ptr(U p, see below d) noexcept; template<class U> unique_ptr(U p, see below d) noexcept; unique_ptr(unique_ptr&& u) noexcept; template<class U, class E> unique_ptr(unique_ptr<U, E>&& u) noexcept; constexpr unique_ptr(nullptr_t) noexcept; // destructor ~unique_ptr(); // assignment unique_ptr& operator=(unique_ptr&& u) noexcept; template<class U, class E> unique_ptr& operator=(unique_ptr<U, E>&& u) noexcept; unique_ptr& operator=(nullptr_t) noexcept; // [unique.ptr.runtime.observers], observers T& operator[](size_t i) const; pointer get() const noexcept; deleter_type& get_deleter() noexcept; const deleter_type& get_deleter() const noexcept; explicit operator bool() const noexcept; // [unique.ptr.runtime.modifiers], modifiers pointer release() noexcept; template<class U> void reset(U p) noexcept; void reset(nullptr_t = nullptr) noexcept; void swap(unique_ptr& u) noexcept; // disable copy from lvalue unique_ptr(const unique_ptr&) = delete; unique_ptr& operator=(const unique_ptr&) = delete; }; }
1
#
A specialization for array types is provided with a slightly altered interface.
  • (1.1)
    Conversions between different types of unique_­ptr<T[], D> that would be disallowed for the corresponding pointer-to-array types, and conversions to or from the non-array forms of unique_­ptr, produce an ill-formed program.
  • (1.2)
    Pointers to types derived from T are rejected by the constructors, and by reset.
  • (1.3)
    The observers operator* and operator-> are not provided.
  • (1.4)
    The indexing observer operator[] is provided.
  • (1.5)
    The default deleter will call delete[].
2
#
Descriptions are provided below only for members that differ from the primary template.
3
#
The template argument T shall be a complete type.

20.11.1.4.2 Constructors [unique.ptr.runtime.ctor]

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template<class U> explicit unique_ptr(U p) noexcept;
1
#
This constructor behaves the same as the constructor in the primary template that takes a single parameter of type pointer.
2
#
Constraints:
  • (2.1)
    U is the same type as pointer, or
  • (2.2)
    pointer is the same type as element_­type*, U is a pointer type V*, and V(*)[] is convertible to element_­type(*)[].
🔗
template<class U> unique_ptr(U p, see below d) noexcept; template<class U> unique_ptr(U p, see below d) noexcept;
3
#
These constructors behave the same as the constructors in the primary template that take a parameter of type pointer and a second parameter.
4
#
Constraints:
  • (4.1)
    U is the same type as pointer,
  • (4.2)
    U is nullptr_­t, or
  • (4.3)
    pointer is the same type as element_­type*, U is a pointer type V*, and V(*)[] is convertible to element_­type(*)[].
🔗
template<class U, class E> unique_ptr(unique_ptr<U, E>&& u) noexcept;
5
#
This constructor behaves the same as in the primary template.
6
#
Constraints: Where UP is unique_­ptr<U, E>:
  • (6.1)
    U is an array type, and
  • (6.2)
    pointer is the same type as element_­type*, and
  • (6.3)
    UP​::​pointer is the same type as UP​::​element_­type*, and
  • (6.4)
    UP​::​element_­type(*)[] is convertible to element_­type(*)[], and
  • (6.5)
    either D is a reference type and E is the same type as D, or D is not a reference type and E is implicitly convertible to D.
[Note 1:
This replaces the Constraints: specification of the primary template.
— end note]

20.11.1.4.3 Assignment [unique.ptr.runtime.asgn]

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template<class U, class E> unique_ptr& operator=(unique_ptr<U, E>&& u) noexcept;
1
#
This operator behaves the same as in the primary template.
2
#
Constraints: Where UP is unique_­ptr<U, E>:
  • (2.1)
    U is an array type, and
  • (2.2)
    pointer is the same type as element_­type*, and
  • (2.3)
    UP​::​pointer is the same type as UP​::​element_­type*, and
  • (2.4)
    UP​::​element_­type(*)[] is convertible to element_­type(*)[], and
  • (2.5)
    is_­assignable_­v<D&, E&&> is true.
[Note 1:
This replaces the Constraints: specification of the primary template.
— end note]

20.11.1.4.4 Observers [unique.ptr.runtime.observers]

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T& operator[](size_t i) const;
1
#
Preconditions: the number of elements in the array to which the stored pointer points.
2
#
Returns: get()[i].

20.11.1.4.5 Modifiers [unique.ptr.runtime.modifiers]

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void reset(nullptr_t p = nullptr) noexcept;
1
#
Effects: Equivalent to reset(pointer()).
🔗
template<class U> void reset(U p) noexcept;
2
#
This function behaves the same as the reset member of the primary template.
3
#
Constraints:
  • (3.1)
    U is the same type as pointer, or
  • (3.2)
    pointer is the same type as element_­type*, U is a pointer type V*, and V(*)[] is convertible to element_­type(*)[].

20.11.1.5 Creation [unique.ptr.create]

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template<class T, class... Args> unique_ptr<T> make_unique(Args&&... args);
1
#
Constraints: T is not an array type.
2
#
Returns: unique_­ptr<T>(new T(std​::​forward<Args>(args)...)).
🔗
template<class T> unique_ptr<T> make_unique(size_t n);
3
#
Constraints: T is an array of unknown bound.
4
#
Returns: unique_­ptr<T>(new remove_­extent_­t<T>[n]()).
🔗
template<class T, class... Args> unspecified make_unique(Args&&...) = delete;
5
#
Constraints: T is an array of known bound.
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template<class T> unique_ptr<T> make_unique_for_overwrite();
6
#
Constraints: T is not an array type.
7
#
Returns: unique_­ptr<T>(new T).
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template<class T> unique_ptr<T> make_unique_for_overwrite(size_t n);
8
#
Constraints: T is an array of unknown bound.
9
#
Returns: unique_­ptr<T>(new remove_­extent_­t<T>[n]).
🔗
template<class T, class... Args> unspecified make_unique_for_overwrite(Args&&...) = delete;
10
#
Constraints: T is an array of known bound.

20.11.1.6 Specialized algorithms [unique.ptr.special]

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template<class T, class D> void swap(unique_ptr<T, D>& x, unique_ptr<T, D>& y) noexcept;
1
#
Constraints: is_­swappable_­v<D> is true.
2
#
Effects: Calls x.swap(y).
🔗
template<class T1, class D1, class T2, class D2> bool operator==(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
3
#
Returns: x.get() == y.get().
🔗
template<class T1, class D1, class T2, class D2> bool operator<(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
4
#
Let CT denote common_type_t<typename unique_ptr<T1, D1>::pointer, typename unique_ptr<T2, D2>::pointer>
5
#
Mandates:
  • (5.1)
    unique_­ptr<T1, D1>​::​pointer is implicitly convertible to CT and
  • (5.2)
    unique_­ptr<T2, D2>​::​pointer is implicitly convertible to CT.
6
#
Preconditions: The specialization less<CT> is a function object type ([function.objects]) that induces a strict weak ordering ([alg.sorting]) on the pointer values.
7
#
Returns: less<CT>()(x.get(), y.get()).
🔗
template<class T1, class D1, class T2, class D2> bool operator>(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
8
#
Returns: y < x.
🔗
template<class T1, class D1, class T2, class D2> bool operator<=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
9
#
Returns: !(y < x).
🔗
template<class T1, class D1, class T2, class D2> bool operator>=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
10
#
Returns: !(x < y).
🔗
template<class T1, class D1, class T2, class D2> requires three_­way_­comparable_­with<typename unique_ptr<T1, D1>::pointer, typename unique_ptr<T2, D2>::pointer> compare_three_way_result_t<typename unique_ptr<T1, D1>::pointer, typename unique_ptr<T2, D2>::pointer> operator<=>(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);
11
#
Returns: compare_­three_­way()(x.get(), y.get()).
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template<class T, class D> bool operator==(const unique_ptr<T, D>& x, nullptr_t) noexcept;
12
#
Returns: !x.
🔗
template<class T, class D> bool operator<(const unique_ptr<T, D>& x, nullptr_t); template<class T, class D> bool operator<(nullptr_t, const unique_ptr<T, D>& x);
13
#
Preconditions: The specialization less<unique_­ptr<T, D>​::​pointer> is a function object type ([function.objects]) that induces a strict weak ordering ([alg.sorting]) on the pointer values.
14
#
Returns: The first function template returns less<unique_ptr<T, D>::pointer>()(x.get(), nullptr)
The second function template returns less<unique_ptr<T, D>::pointer>()(nullptr, x.get())
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template<class T, class D> bool operator>(const unique_ptr<T, D>& x, nullptr_t); template<class T, class D> bool operator>(nullptr_t, const unique_ptr<T, D>& x);
15
#
Returns: The first function template returns nullptr < x.
The second function template returns x < nullptr.
🔗
template<class T, class D> bool operator<=(const unique_ptr<T, D>& x, nullptr_t); template<class T, class D> bool operator<=(nullptr_t, const unique_ptr<T, D>& x);
16
#
Returns: The first function template returns !(nullptr < x).
The second function template returns !(x < nullptr).
🔗
template<class T, class D> bool operator>=(const unique_ptr<T, D>& x, nullptr_t); template<class T, class D> bool operator>=(nullptr_t, const unique_ptr<T, D>& x);
17
#
Returns: The first function template returns !(x < nullptr).
The second function template returns !(nullptr < x).
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template<class T, class D> requires three_­way_­comparable_­with<typename unique_ptr<T, D>::pointer, nullptr_t> compare_three_way_result_t<typename unique_ptr<T, D>::pointer, nullptr_t> operator<=>(const unique_ptr<T, D>& x, nullptr_t);
18
#
Returns: compare_­three_­way()(x.get(), nullptr).

20.11.1.7 I/O [unique.ptr.io]

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template<class E, class T, class Y, class D> basic_ostream<E, T>& operator<<(basic_ostream<E, T>& os, const unique_ptr<Y, D>& p);
1
#
Constraints: os << p.get() is a valid expression.
2
#
Effects: Equivalent to: os << p.get();
3
#
Returns: os.