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Smart Pointers to boost your code

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

//
//  intrusive_ptr.hpp
//
//  Copyright (c) 2001, 2002 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/intrusive_ptr.html for documentation.
//

#include <boost/config.hpp>

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

#include <boost/assert.hpp>
#include <boost/detail/workaround.hpp>

#include <functional>           // for std::less
#include <iosfwd>               // for std::basic_ostream


namespace boost
{

//
//  intrusive_ptr
//
//  A smart pointer that uses intrusive reference counting.
//
//  Relies on unqualified calls to
//  
//      void intrusive_ptr_add_ref(T * p);
//      void intrusive_ptr_release(T * p);
//
//          (p != 0)
//
//  The object is responsible for destroying itself.
//

template<class T> class intrusive_ptr
{
private:

    typedef intrusive_ptr this_type;

public:

    typedef T element_type;

    intrusive_ptr(): p_(0)
    {
    }

    intrusive_ptr(T * p, bool add_ref = true): p_(p)
    {
        if(p_ != 0 && add_ref) intrusive_ptr_add_ref(p_);
    }

#if !defined(BOOST_NO_MEMBER_TEMPLATES) || defined(BOOST_MSVC6_MEMBER_TEMPLATES)

    template<class U> intrusive_ptr(intrusive_ptr<U> const & rhs): p_(rhs.get())
    {
        if(p_ != 0) intrusive_ptr_add_ref(p_);
    }

#endif

    intrusive_ptr(intrusive_ptr const & rhs): p_(rhs.p_)
    {
        if(p_ != 0) intrusive_ptr_add_ref(p_);
    }

    ~intrusive_ptr()
    {
        if(p_ != 0) intrusive_ptr_release(p_);
    }

#if !defined(BOOST_NO_MEMBER_TEMPLATES) || defined(BOOST_MSVC6_MEMBER_TEMPLATES)

    template<class U> intrusive_ptr & operator=(intrusive_ptr<U> const & rhs)
    {
        this_type(rhs).swap(*this);
        return *this;
    }

#endif

    intrusive_ptr & operator=(intrusive_ptr const & rhs)
    {
        this_type(rhs).swap(*this);
        return *this;
    }

    intrusive_ptr & operator=(T * rhs)
    {
        this_type(rhs).swap(*this);
        return *this;
    }

    T * get() const
    {
        return p_;
    }

    T & operator*() const
    {
        return *p_;
    }

    T * operator->() const
    {
        return p_;
    }

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

    operator bool () const
    {
        return p_ != 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 p_ == 0? 0: &this_type::get;
    }

#else 

    typedef T * this_type::*unspecified_bool_type;

    operator unspecified_bool_type () const
    {
        return p_ == 0? 0: &this_type::p_;
    }

#endif

    // operator! is a Borland-specific workaround
    bool operator! () const
    {
        return p_ == 0;
    }

    void swap(intrusive_ptr & rhs)
    {
        T * tmp = p_;
        p_ = rhs.p_;
        rhs.p_ = tmp;
    }

private:

    T * p_;
};

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

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

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

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

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

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

#endif

template<class T> inline bool operator<(intrusive_ptr<T> const & a, intrusive_ptr<T> const & b)
{
    return std::less<T *>()(a.get(), b.get());
}

template<class T> void swap(intrusive_ptr<T> & lhs, intrusive_ptr<T> & rhs)
{
    lhs.swap(rhs);
}

// mem_fn support

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

template<class T, class U> intrusive_ptr<T> static_pointer_cast(intrusive_ptr<U> const & p)
{
    return static_cast<T *>(p.get());
}

template<class T, class U> intrusive_ptr<T> const_pointer_cast(intrusive_ptr<U> const & p)
{
    return const_cast<T *>(p.get());
}

template<class T, class U> intrusive_ptr<T> dynamic_pointer_cast(intrusive_ptr<U> const & p)
{
    return dynamic_cast<T *>(p.get());
}

// operator<<

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

template<class Y> std::ostream & operator<< (std::ostream & os, intrusive_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, intrusive_ptr<Y> const & p)
# else
template<class E, class T, class Y> std::basic_ostream<E, T> & operator<< (std::basic_ostream<E, T> & os, intrusive_ptr<Y> const & p)
# endif 
{
    os << p.get();
    return os;
}

#endif

} // namespace boost

#ifdef BOOST_MSVC
# pragma warning(pop)
#endif    

#endif  // #ifndef BOOST_INTRUSIVE_PTR_HPP_INCLUDED

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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.
 
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