Click here to Skip to main content
Click here to Skip to main content
Add your own
alternative version

Smart Pointers to boost your code

, 27 Sep 2004
A beginner's introduction to the smart pointers provided by the boost library.
#ifndef BOOST_SHARED_PTR_HPP_INCLUDED
#define BOOST_SHARED_PTR_HPP_INCLUDED

//
//  shared_ptr.hpp
//
//  (C) Copyright Greg Colvin and Beman Dawes 1998, 1999.
//  Copyright (c) 2001, 2002, 2003 Peter Dimov
//
//  Permission to copy, use, modify, sell and distribute this software
//  is granted provided this copyright notice appears in all copies.
//  This software is provided "as is" without express or implied
//  warranty, and with no claim as to its suitability for any purpose.
//
//  See http://www.boost.org/libs/smart_ptr/shared_ptr.htm for documentation.
//

#include <boost/config.hpp>   // for broken compiler workarounds

#if defined(BOOST_NO_MEMBER_TEMPLATES) && !defined(BOOST_MSVC6_MEMBER_TEMPLATES)
#include <boost/detail/shared_ptr_nmt.hpp>
#else

#include <boost/assert.hpp>
#include <boost/checked_delete.hpp>
#include <boost/throw_exception.hpp>
#include <boost/detail/shared_count.hpp>
#include <boost/detail/workaround.hpp>

#include <memory>               // for std::auto_ptr
#include <algorithm>            // for std::swap
#include <functional>           // for std::less
#include <typeinfo>             // for std::bad_cast
#include <iosfwd>               // for std::basic_ostream

#ifdef BOOST_MSVC  // moved here to work around VC++ compiler crash
# pragma warning(push)
# pragma warning(disable:4284) // odd return type for operator->
#endif

namespace boost
{

template<class T> class weak_ptr;
template<class T> class enable_shared_from_this;

namespace detail
{

struct static_cast_tag {};
struct const_cast_tag {};
struct dynamic_cast_tag {};
struct polymorphic_cast_tag {};

template<class T> struct shared_ptr_traits
{
    typedef T & reference;
};

template<> struct shared_ptr_traits<void>
{
    typedef void reference;
};

#if !defined(BOOST_NO_CV_VOID_SPECIALIZATIONS)

template<> struct shared_ptr_traits<void const>
{
    typedef void reference;
};

template<> struct shared_ptr_traits<void volatile>
{
    typedef void reference;
};

template<> struct shared_ptr_traits<void const volatile>
{
    typedef void reference;
};

#endif

// enable_shared_from_this support

template<class T, class Y> void sp_enable_shared_from_this(boost::enable_shared_from_this<T> * pe, Y * px, shared_count const & pn)
{
    if(pe != 0) pe->_internal_weak_this._internal_assign(px, pn);
}

inline void sp_enable_shared_from_this(void const volatile *, void const volatile *, shared_count const &)
{
}

} // namespace detail


//
//  shared_ptr
//
//  An enhanced relative of scoped_ptr with reference counted copy semantics.
//  The object pointed to is deleted when the last shared_ptr pointing to it
//  is destroyed or reset.
//

template<class T> class shared_ptr
{
private:

    // Borland 5.5.1 specific workaround
    typedef shared_ptr<T> this_type;

public:

    typedef T element_type;
    typedef T value_type;
    typedef T * pointer;
    typedef typename detail::shared_ptr_traits<T>::reference reference;

    shared_ptr(): px(0), pn() // never throws in 1.30+
    {
    }

    template<class Y>
    explicit shared_ptr(Y * p): px(p), pn(p, checked_deleter<Y>()) // Y must be complete
    {
        detail::sp_enable_shared_from_this(p, p, pn);
    }

    //
    // Requirements: D's copy constructor must not throw
    //
    // shared_ptr will release p by calling d(p)
    //

    template<class Y, class D> shared_ptr(Y * p, D d): px(p), pn(p, d)
    {
        detail::sp_enable_shared_from_this(p, p, pn);
    }

//  generated copy constructor, assignment, destructor are fine...

//  except that Borland C++ has a bug, and g++ with -Wsynth warns
#if defined(__BORLANDC__) || defined(__GNUC__)

    shared_ptr & operator=(shared_ptr const & r) // never throws
    {
        px = r.px;
        pn = r.pn; // shared_count::op= doesn't throw
        return *this;
    }

#endif

    template<class Y>
    explicit shared_ptr(weak_ptr<Y> const & r): pn(r.pn) // may throw
    {
        // it is now safe to copy r.px, as pn(r.pn) did not throw
        px = r.px;
    }

    template<class Y>
    shared_ptr(shared_ptr<Y> const & r): px(r.px), pn(r.pn) // never throws
    {
    }

    template<class Y>
    shared_ptr(shared_ptr<Y> const & r, detail::static_cast_tag): px(static_cast<element_type *>(r.px)), pn(r.pn)
    {
    }

    template<class Y>
    shared_ptr(shared_ptr<Y> const & r, detail::const_cast_tag): px(const_cast<element_type *>(r.px)), pn(r.pn)
    {
    }

    template<class Y>
    shared_ptr(shared_ptr<Y> const & r, detail::dynamic_cast_tag): px(dynamic_cast<element_type *>(r.px)), pn(r.pn)
    {
        if(px == 0) // need to allocate new counter -- the cast failed
        {
            pn = detail::shared_count();
        }
    }

    template<class Y>
    shared_ptr(shared_ptr<Y> const & r, detail::polymorphic_cast_tag): px(dynamic_cast<element_type *>(r.px)), pn(r.pn)
    {
        if(px == 0)
        {
            boost::throw_exception(std::bad_cast());
        }
    }

#ifndef BOOST_NO_AUTO_PTR

    template<class Y>
    explicit shared_ptr(std::auto_ptr<Y> & r): px(r.get()), pn()
    {
        Y * tmp = r.get();
        pn = detail::shared_count(r);
        detail::sp_enable_shared_from_this(tmp, tmp, pn);
    }

#endif

#if !defined(BOOST_MSVC) || (BOOST_MSVC > 1200)

    template<class Y>
    shared_ptr & operator=(shared_ptr<Y> const & r) // never throws
    {
        px = r.px;
        pn = r.pn; // shared_count::op= doesn't throw
        return *this;
    }

#endif

#ifndef BOOST_NO_AUTO_PTR

    template<class Y>
    shared_ptr & operator=(std::auto_ptr<Y> & r)
    {
        this_type(r).swap(*this);
        return *this;
    }

#endif

    void reset() // never throws in 1.30+
    {
        this_type().swap(*this);
    }

    template<class Y> void reset(Y * p) // Y must be complete
    {
        BOOST_ASSERT(p == 0 || p != px); // catch self-reset errors
        this_type(p).swap(*this);
    }

    template<class Y, class D> void reset(Y * p, D d)
    {
        this_type(p, d).swap(*this);
    }

    reference operator* () const // never throws
    {
        BOOST_ASSERT(px != 0);
        return *px;
    }

    T * operator-> () const // never throws
    {
        BOOST_ASSERT(px != 0);
        return px;
    }
    
    T * get() const // never throws
    {
        return px;
    }

    // implicit conversion to "bool"

#if defined(__SUNPRO_CC) && BOOST_WORKAROUND(__SUNPRO_CC, <= 0x530)

    operator bool () const
    {
        return px != 0;
    }

#elif defined(__MWERKS__) && BOOST_WORKAROUND(__MWERKS__, BOOST_TESTED_AT(0x3003))
    typedef T * (this_type::*unspecified_bool_type)() const;
    
    operator unspecified_bool_type() const // never throws
    {
        return px == 0? 0: &this_type::get;
    }

#else 

    typedef T * this_type::*unspecified_bool_type;

    operator unspecified_bool_type() const // never throws
    {
        return px == 0? 0: &this_type::px;
    }

#endif

    // operator! is redundant, but some compilers need it

    bool operator! () const // never throws
    {
        return px == 0;
    }

    bool unique() const // never throws
    {
        return pn.unique();
    }

    long use_count() const // never throws
    {
        return pn.use_count();
    }

    void swap(shared_ptr<T> & other) // never throws
    {
        std::swap(px, other.px);
        pn.swap(other.pn);
    }

    template<class Y> bool _internal_less(shared_ptr<Y> const & rhs) const
    {
        return pn < rhs.pn;
    }

    void * _internal_get_deleter(std::type_info const & ti) const
    {
        return pn.get_deleter(ti);
    }

// Tasteless as this may seem, making all members public allows member templates
// to work in the absence of member template friends. (Matthew Langston)

#ifndef BOOST_NO_MEMBER_TEMPLATE_FRIENDS

private:

    template<class Y> friend class shared_ptr;
    template<class Y> friend class weak_ptr;


#endif

    T * px;                     // contained pointer
    detail::shared_count pn;    // reference counter

};  // shared_ptr

template<class T, class U> inline bool operator==(shared_ptr<T> const & a, shared_ptr<U> const & b)
{
    return a.get() == b.get();
}

template<class T, class U> inline bool operator!=(shared_ptr<T> const & a, shared_ptr<U> const & b)
{
    return a.get() != b.get();
}

#if __GNUC__ == 2 && __GNUC_MINOR__ <= 96

// Resolve the ambiguity between our op!= and the one in rel_ops

template<class T> inline bool operator!=(shared_ptr<T> const & a, shared_ptr<T> const & b)
{
    return a.get() != b.get();
}

#endif

template<class T, class U> inline bool operator<(shared_ptr<T> const & a, shared_ptr<U> const & b)
{
    return a._internal_less(b);
}

template<class T> inline void swap(shared_ptr<T> & a, shared_ptr<T> & b)
{
    a.swap(b);
}

template<class T, class U> shared_ptr<T> static_pointer_cast(shared_ptr<U> const & r)
{
    return shared_ptr<T>(r, detail::static_cast_tag());
}

template<class T, class U> shared_ptr<T> const_pointer_cast(shared_ptr<U> const & r)
{
    return shared_ptr<T>(r, detail::const_cast_tag());
}

template<class T, class U> shared_ptr<T> dynamic_pointer_cast(shared_ptr<U> const & r)
{
    return shared_ptr<T>(r, detail::dynamic_cast_tag());
}

// shared_*_cast names are deprecated. Use *_pointer_cast instead.

template<class T, class U> shared_ptr<T> shared_static_cast(shared_ptr<U> const & r)
{
    return shared_ptr<T>(r, detail::static_cast_tag());
}

template<class T, class U> shared_ptr<T> shared_dynamic_cast(shared_ptr<U> const & r)
{
    return shared_ptr<T>(r, detail::dynamic_cast_tag());
}

template<class T, class U> shared_ptr<T> shared_polymorphic_cast(shared_ptr<U> const & r)
{
    return shared_ptr<T>(r, detail::polymorphic_cast_tag());
}

template<class T, class U> shared_ptr<T> shared_polymorphic_downcast(shared_ptr<U> const & r)
{
    BOOST_ASSERT(dynamic_cast<T *>(r.get()) == r.get());
    return shared_static_cast<T>(r);
}

// get_pointer() enables boost::mem_fn to recognize shared_ptr

template<class T> inline T * get_pointer(shared_ptr<T> const & p)
{
    return p.get();
}

// operator<<

#if defined(__GNUC__) &&  (__GNUC__ < 3)

template<class Y> std::ostream & operator<< (std::ostream & os, shared_ptr<Y> const & p)
{
    os << p.get();
    return os;
}

#else

# if defined(BOOST_MSVC) && BOOST_WORKAROUND(BOOST_MSVC, <= 1200 && __SGI_STL_PORT)
// MSVC6 has problems finding std::basic_ostream through the using declaration in namespace _STL
using std::basic_ostream;
template<class E, class T, class Y> basic_ostream<E, T> & operator<< (basic_ostream<E, T> & os, shared_ptr<Y> const & p)
# else
template<class E, class T, class Y> std::basic_ostream<E, T> & operator<< (std::basic_ostream<E, T> & os, shared_ptr<Y> const & p)
# endif 
{
    os << p.get();
    return os;
}

#endif

// get_deleter (experimental)

#if (defined(__GNUC__) &&  (__GNUC__ < 3)) || (defined(__EDG_VERSION__) && (__EDG_VERSION__ <= 238))

// g++ 2.9x doesn't allow static_cast<X const *>(void *)
// apparently EDG 2.38 also doesn't accept it

template<class D, class T> D * get_deleter(shared_ptr<T> const & p)
{
    void const * q = p._internal_get_deleter(typeid(D));
    return const_cast<D *>(static_cast<D const *>(q));
}

#else

template<class D, class T> D * get_deleter(shared_ptr<T> const & p)
{
    return static_cast<D *>(p._internal_get_deleter(typeid(D)));
}

#endif

} // namespace boost

#ifdef BOOST_MSVC
# pragma warning(pop)
#endif    

#endif  // #if defined(BOOST_NO_MEMBER_TEMPLATES) && !defined(BOOST_MSVC6_MEMBER_TEMPLATES)

#endif  // #ifndef BOOST_SHARED_PTR_HPP_INCLUDED

By viewing downloads associated with this article you agree to the Terms of Service and the article's licence.

If a file you wish to view isn't highlighted, and is a text file (not binary), please let us know and we'll add colourisation support for it.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Share

About the Author

peterchen
Klippel
Germany Germany
Peter is tired of being called "Mr. Chen", even so certain individuals insist on it. No, he's not chinese.
 
Peter has seen lots of boxes you youngsters wouldn't even accept as calculators. He is proud of having visited the insides of a 16 Bit Machine.
 
In his spare time he ponders new ways of turning groceries into biohazards, or tries to coax South American officials to add some stamps to his passport.
 
Beyond these trivialities Peter works for Klippel[^], a small german company that wants to make mankind happier by selling them novel loudspeaker measurement equipment.
 

Where are you from?[^]



Please, if you are using one of my articles for anything, just leave me a comment. Seeing that this stuff is actually useful to someone is what keeps me posting and updating them.
Should you happen to not like it, tell me, too

| Advertise | Privacy | Mobile
Web04 | 2.8.140827.1 | Last Updated 27 Sep 2004
Article Copyright 2004 by peterchen
Everything else Copyright © CodeProject, 1999-2014
Terms of Service
Layout: fixed | fluid