std::auto_ptr< _Tp >

Section: C Library Functions (3)
Updated: Wed Apr 17 2019
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NAME

std::auto_ptr< _Tp > - A simple smart pointer providing strict ownership semantics.

SYNOPSIS

Public Types

typedef _Tp element_type
The pointed-to type.

Public Member Functions

auto_ptr (element_type *__p=0) throw ()
An auto_ptr is usually constructed from a raw pointer.
auto_ptr (auto_ptr &__a) throw ()
An auto_ptr can be constructed from another auto_ptr.
template<typename _Tp1 > auto_ptr (auto_ptr< _Tp1 > &__a) throw ()
An auto_ptr can be constructed from another auto_ptr.
auto_ptr (auto_ptr_ref< element_type > __ref) throw ()
Automatic conversions.
~auto_ptr ()

element_type * get () const throw ()
Bypassing the smart pointer.
element_type & operator * () const throw ()
Smart pointer dereferencing.
template<typename _Tp1 > operator auto_ptr< _Tp1 > () throw ()

template<typename _Tp1 > operator auto_ptr_ref< _Tp1 > () throw ()

element_type * operator-> () const throw ()
Smart pointer dereferencing.
auto_ptr & operator= (auto_ptr &__a) throw ()
auto_ptr assignment operator.
template<typename _Tp1 > auto_ptr & operator= (auto_ptr< _Tp1 > &__a) throw ()
auto_ptr assignment operator.
auto_ptr & operator= (auto_ptr_ref< element_type > __ref) throw ()

element_type * release () throw ()
Bypassing the smart pointer.
void reset (element_type *__p=0) throw ()
Forcibly deletes the managed object.

Detailed Description

template<typename _Tp>

class std::auto_ptr< _Tp >" A simple smart pointer providing strict ownership semantics.

The Standard says:


An auto_ptr owns the object it holds a pointer to.  Copying
an auto_ptr copies the pointer and transfers ownership to the
destination.  If more than one auto_ptr owns the same object
at the same time the behavior of the program is undefined.

The uses of auto_ptr include providing temporary
exception-safety for dynamically allocated memory, passing
ownership of dynamically allocated memory to a function, and
returning dynamically allocated memory from a function.  auto_ptr does not meet the CopyConstructible and Assignable
requirements for Standard Library container elements and thus
instantiating a Standard Library container with an auto_ptr results in undefined behavior.

Quoted from [20.4.5]/3.

Good examples of what can and cannot be done with auto_ptr can be found in the libstdc++ testsuite.

_GLIBCXX_RESOLVE_LIB_DEFECTS 127. auto_ptr<> conversion issues These resolutions have all been incorporated.

Definition at line 89 of file auto_ptr.h.

Member Typedef Documentation

template<typename _Tp> typedef _Tp std::auto_ptr< _Tp >::element_type

The pointed-to type.

Definition at line 96 of file auto_ptr.h.

Constructor & Destructor Documentation

template<typename _Tp> std::auto_ptr< _Tp >::auto_ptr (element_type * __p = 0) [inline], [explicit]

An auto_ptr is usually constructed from a raw pointer.

Parameters:

: __p A pointer (defaults to NULL).

This object now owns the object pointed to by __p.

Definition at line 105 of file auto_ptr.h.

template<typename _Tp> std::auto_ptr< _Tp >::auto_ptr (auto_ptr< _Tp > & __a) [inline]

An auto_ptr can be constructed from another auto_ptr.

Parameters:

: __a Another auto_ptr of the same type.

This object now owns the object previously owned by __a, which has given up ownership.

Definition at line 114 of file auto_ptr.h.

template<typename _Tp> template<typename _Tp1 > std::auto_ptr< _Tp >::auto_ptr (auto_ptr< _Tp1 > & __a) [inline]

An auto_ptr can be constructed from another auto_ptr.

Parameters:

: __a Another auto_ptr of a different but related type.

A pointer-to-Tp1 must be convertible to a pointer-to-Tp/element_type.

This object now owns the object previously owned by __a, which has given up ownership.

Definition at line 127 of file auto_ptr.h.

template<typename _Tp> std::auto_ptr< _Tp >::~auto_ptr () [inline]

When the auto_ptr goes out of scope, the object it owns is deleted. If it no longer owns anything (i.e., get() is NULL), then this has no effect.

The C++ standard says there is supposed to be an empty throw specification here, but omitting it is standard conforming. Its presence can be detected only if _Tp::~_Tp() throws, but this is prohibited. [17.4.3.6]/2

Definition at line 172 of file auto_ptr.h.

template<typename _Tp> std::auto_ptr< _Tp >::auto_ptr (auto_ptr_ref< element_type > __ref) [inline]

Automatic conversions. These operations are supposed to convert an auto_ptr into and from an auto_ptr_ref automatically as needed. This would allow constructs such as

auto_ptr<Derived>  func_returning_auto_ptr(.....);
...
auto_ptr<Base> ptr = func_returning_auto_ptr(.....);

But it doesn't work, and won't be fixed. For further details see http://cplusplus.github.io/LWG/lwg-closed.html#463

Definition at line 266 of file auto_ptr.h.

Member Function Documentation

template<typename _Tp> element_type* std::auto_ptr< _Tp >::get (void) const [inline]

Bypassing the smart pointer.

Returns:

: The raw pointer being managed.

You can get a copy of the pointer that this object owns, for situations such as passing to a function which only accepts a raw pointer.

Note:

: This auto_ptr still owns the memory.

Definition at line 213 of file auto_ptr.h.

template<typename _Tp> element_type& std::auto_ptr< _Tp >::operator * () const [inline]

Smart pointer dereferencing. If this auto_ptr no longer owns anything, then this operation will crash. (For a smart pointer, no longer owns anything is the same as being a null pointer, and you know what happens when you dereference one of those...)

Definition at line 183 of file auto_ptr.h.

template<typename _Tp> element_type* std::auto_ptr< _Tp >::operator-> () const [inline]

Smart pointer dereferencing. This returns the pointer itself, which the language then will automatically cause to be dereferenced.

Definition at line 196 of file auto_ptr.h.

template<typename _Tp> auto_ptr& std::auto_ptr< _Tp >::operator= (auto_ptr< _Tp > & __a) [inline]

auto_ptr assignment operator.

Parameters:

: __a Another auto_ptr of the same type.

This object now owns the object previously owned by __a, which has given up ownership. The object that this one used to own and track has been deleted.

Definition at line 138 of file auto_ptr.h.

References std::auto_ptr< _Tp >::reset().

template<typename _Tp> template<typename _Tp1 > auto_ptr& std::auto_ptr< _Tp >::operator= (auto_ptr< _Tp1 > & __a) [inline]

auto_ptr assignment operator.

Parameters:

: __a Another auto_ptr of a different but related type.

A pointer-to-Tp1 must be convertible to a pointer-to-Tp/element_type.

This object now owns the object previously owned by __a, which has given up ownership. The object that this one used to own and track has been deleted.

Definition at line 156 of file auto_ptr.h.

References std::auto_ptr< _Tp >::reset().

template<typename _Tp> element_type* std::auto_ptr< _Tp >::release () [inline]

Bypassing the smart pointer.

Returns:

: The raw pointer being managed.

You can get a copy of the pointer that this object owns, for situations such as passing to a function which only accepts a raw pointer.

Note:

: This auto_ptr no longer owns the memory. When this object goes out of scope, nothing will happen.

Definition at line 227 of file auto_ptr.h.

template<typename _Tp> void std::auto_ptr< _Tp >::reset (element_type * __p = 0) [inline]

Forcibly deletes the managed object.

Parameters:

: __p A pointer (defaults to NULL).

This object now owns the object pointed to by __p. The previous object has been deleted.

Definition at line 242 of file auto_ptr.h.

Referenced by std::auto_ptr< _Tp >::operator=().

Author

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