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最近观看Boost库源代码。Boost功能强大的库,但它的许多源代码,十一细读太费时间,毕竟,还有其他东西要学。所以我决定脱脂感兴趣的章节,他们的设计思路和难以理解的地方记录。
shared_ptr是Boost里面最有价值的的智能指针。
它封装了一个原生态指针和一个引用计数器,这个引用计数器是一个类shared_count。shared_ptr支持比較运算,重载了operator<,因此其能够用于set和map。
在转换shared_ptr指针时。用***_pointer_cast定义的函数来转换(返回shared_ptr<T>类型),假设使用static_cast、reinterpret_cast等将会造成shared_ptr无法正确管理指针。
template<class T> class shared_ptr { private: // Borland 5.5.1 specific workaround typedef shared_ptr<T> this_type; public: typedef typename boost::detail::sp_element< T >::type element_type; //以下有多种构造函数,为了适应不同情境须要 //默认构造函数。px为指针。pn为计数器(它是一个类shared_count,其默认构造函数设其值为0) shared_ptr() BOOST_NOEXCEPT : px( 0 ), pn() // never throws in 1.30+ { } #if !defined( BOOST_NO_CXX11_NULLPTR ) shared_ptr( boost::detail::sp_nullptr_t ) BOOST_NOEXCEPT : px( 0 ), pn() // never throws { } #endif //用Y类型来初始化。Y可能与T是不同类型 template<class Y> explicit shared_ptr( Y * p ): px( p ), pn() // Y must be complete { boost::detail::sp_pointer_construct( this, 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 ) { boost::detail::sp_deleter_construct( this, p ); } #if !defined( BOOST_NO_CXX11_NULLPTR ) template<class D> shared_ptr( boost::detail::sp_nullptr_t p, D d ): px( p ), pn( p, d ) { } #endif // As above, but with allocator. A's copy constructor shall not throw. template<class Y, class D, class A> shared_ptr( Y * p, D d, A a ): px( p ), pn( p, d, a ) { boost::detail::sp_deleter_construct( this, p ); } #if !defined( BOOST_NO_CXX11_NULLPTR ) template<class D, class A> shared_ptr( boost::detail::sp_nullptr_t p, D d, A a ): px( p ), pn( p, d, a ) { } #endif // generated copy constructor, destructor are fine... #if !defined( BOOST_NO_CXX11_RVALUE_REFERENCES ) // ... except in C++0x, move disables the implicit copy //复制构造函数,两个shared_ptr共同管理一个指针 shared_ptr( shared_ptr const & r ) BOOST_NOEXCEPT : px( r.px ), pn( r.pn ) { } #endif template<class Y> explicit shared_ptr( weak_ptr<Y> const & r ): pn( r.pn ) // may throw { boost::detail::sp_assert_convertible< Y, T >(); // it is now safe to copy r.px, as pn(r.pn) did not throw px = r.px; } template<class Y> shared_ptr( weak_ptr<Y> const & r, boost::detail::sp_nothrow_tag ) BOOST_NOEXCEPT : px( 0 ), pn( r.pn, boost::detail::sp_nothrow_tag() ) { if( !pn.empty() ) { px = r.px; } } template<class Y> #if !defined( BOOST_SP_NO_SP_CONVERTIBLE ) shared_ptr( shared_ptr<Y> const & r, typename boost::detail::sp_enable_if_convertible<Y,T>::type = boost::detail::sp_empty() ) #else shared_ptr( shared_ptr<Y> const & r ) #endif BOOST_NOEXCEPT : px( r.px ), pn( r.pn ) { boost::detail::sp_assert_convertible< Y, T >(); } // aliasing template< class Y > shared_ptr( shared_ptr<Y> const & r, element_type * p ) BOOST_NOEXCEPT : px( p ), pn( r.pn ) { } #ifndef BOOST_NO_AUTO_PTR template<class Y> explicit shared_ptr( std::auto_ptr<Y> & r ): px(r.get()), pn() { boost::detail::sp_assert_convertible< Y, T >(); Y * tmp = r.get(); pn = boost::detail::shared_count( r ); boost::detail::sp_deleter_construct( this, tmp ); } #if !defined( BOOST_NO_CXX11_RVALUE_REFERENCES ) template<class Y> shared_ptr( std::auto_ptr<Y> && r ): px(r.get()), pn() { boost::detail::sp_assert_convertible< Y, T >(); Y * tmp = r.get(); pn = boost::detail::shared_count( r ); boost::detail::sp_deleter_construct( this, tmp ); } #elif !defined( BOOST_NO_SFINAE ) && !defined( BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION ) template<class Ap> explicit shared_ptr( Ap r, typename boost::detail::sp_enable_if_auto_ptr<Ap, int>::type = 0 ): px( r.get() ), pn() { typedef typename Ap::element_type Y; boost::detail::sp_assert_convertible< Y, T >(); Y * tmp = r.get(); pn = boost::detail::shared_count( r ); boost::detail::sp_deleter_construct( this, tmp ); } #endif // BOOST_NO_SFINAE, BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION #endif // BOOST_NO_AUTO_PTR #if !defined( BOOST_NO_CXX11_SMART_PTR ) && !defined( BOOST_NO_CXX11_RVALUE_REFERENCES ) template< class Y, class D > shared_ptr( std::unique_ptr< Y, D > && r ): px( r.get() ), pn() { boost::detail::sp_assert_convertible< Y, T >(); typename std::unique_ptr< Y, D >::pointer tmp = r.get(); pn = boost::detail::shared_count( r ); boost::detail::sp_deleter_construct( this, tmp ); } #endif // assignment //重载赋值操作符 shared_ptr & operator=( shared_ptr const & r ) BOOST_NOEXCEPT { this_type(r).swap(*this); return *this; } #if !defined(BOOST_MSVC) || (BOOST_MSVC >= 1400) template<class Y> shared_ptr & operator=(shared_ptr<Y> const & r) BOOST_NOEXCEPT { this_type(r).swap(*this); 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; } #if !defined( BOOST_NO_CXX11_RVALUE_REFERENCES ) template<class Y> //&&是C++11的新特性,表示右值引用(能够使用暂时对象) shared_ptr & operator=( std::auto_ptr<Y> && r ) { this_type( static_cast< std::auto_ptr<Y> && >( r ) ).swap( *this ); return *this; } #elif !defined( BOOST_NO_SFINAE ) && !defined( BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION ) template<class Ap> typename boost::detail::sp_enable_if_auto_ptr< Ap, shared_ptr & >::type operator=( Ap r ) { this_type( r ).swap( *this ); return *this; } #endif // BOOST_NO_SFINAE, BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION #endif // BOOST_NO_AUTO_PTR #if !defined( BOOST_NO_CXX11_SMART_PTR ) && !defined( BOOST_NO_CXX11_RVALUE_REFERENCES ) template<class Y, class D> shared_ptr & operator=( std::unique_ptr<Y, D> && r ) { this_type( static_cast< std::unique_ptr<Y, D> && >( r ) ).swap(*this); return *this; } #endif // Move support #if !defined( BOOST_NO_CXX11_RVALUE_REFERENCES ) shared_ptr( shared_ptr && r ) BOOST_NOEXCEPT : px( r.px ), pn() { pn.swap( r.pn ); r.px = 0; } template<class Y> #if !defined( BOOST_SP_NO_SP_CONVERTIBLE ) shared_ptr( shared_ptr<Y> && r, typename boost::detail::sp_enable_if_convertible<Y,T>::type = boost::detail::sp_empty() ) #else shared_ptr( shared_ptr<Y> && r ) #endif BOOST_NOEXCEPT : px( r.px ), pn() { boost::detail::sp_assert_convertible< Y, T >(); pn.swap( r.pn ); r.px = 0; } shared_ptr & operator=( shared_ptr && r ) BOOST_NOEXCEPT { this_type( static_cast< shared_ptr && >( r ) ).swap( *this ); return *this; } template<class Y> shared_ptr & operator=( shared_ptr<Y> && r ) BOOST_NOEXCEPT { this_type( static_cast< shared_ptr<Y> && >( r ) ).swap( *this ); return *this; } #endif #if !defined( BOOST_NO_CXX11_NULLPTR ) shared_ptr & operator=( boost::detail::sp_nullptr_t ) BOOST_NOEXCEPT // never throws { this_type().swap(*this); return *this; } #endif void reset() BOOST_NOEXCEPT // never throws in 1.30+ { //this_type()为暂时对象,交换后*this成为默认原始状态 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 ); } template<class Y, class D, class A> void reset( Y * p, D d, A a ) { this_type( p, d, a ).swap( *this ); } template<class Y> void reset( shared_ptr<Y> const & r, element_type * p ) { this_type( r, p ).swap( *this ); } // never throws (but has a BOOST_ASSERT in it, so not marked with BOOST_NOEXCEPT) //重载解引用操作符。返回指针指向的对象 typename boost::detail::sp_dereference< T >::type operator* () const { BOOST_ASSERT( px != 0 ); return *px; } // never throws (but has a BOOST_ASSERT in it, so not marked with BOOST_NOEXCEPT) //重载箭头操作符。返回原生态指针 typename boost::detail::sp_member_access< T >::type operator-> () const { BOOST_ASSERT( px != 0 ); return px; } // never throws (but has a BOOST_ASSERT in it, so not marked with BOOST_NOEXCEPT) //它也能够指向指针,重载了[]操作符 typename boost::detail::sp_array_access< T >::type operator[] ( std::ptrdiff_t i ) const { BOOST_ASSERT( px != 0 ); BOOST_ASSERT( i >= 0 && ( i < boost::detail::sp_extent< T >::value || boost::detail::sp_extent< T >::value == 0 ) ); return px[ i ]; } //get能够得到原生态指针 element_type * get() const BOOST_NOEXCEPT { return px; } // implicit conversion to "bool" #include <boost/smart_ptr/detail/operator_bool.hpp> //能够推断是否指针使用者是否唯一 bool unique() const BOOST_NOEXCEPT { return pn.unique(); } //返回指针使用者的个数,推断是否唯一是unique比use_count()==1快非常多 long use_count() const BOOST_NOEXCEPT { return pn.use_count(); } //上面那么多复制构造函数都用到了swap /* std::swap()源代码非常easy: template <class T> void swap ( T& a, T& b ) { T c(a); a=b; b=c; } */ void swap( shared_ptr & other ) BOOST_NOEXCEPT { std::swap(px, other.px); pn.swap(other.pn); } template<class Y> bool owner_before( shared_ptr<Y> const & rhs ) const BOOST_NOEXCEPT { return pn < rhs.pn; } template<class Y> bool owner_before( weak_ptr<Y> const & rhs ) const BOOST_NOEXCEPT { return pn < rhs.pn; } void * _internal_get_deleter( boost::detail::sp_typeinfo const & ti ) const BOOST_NOEXCEPT { return pn.get_deleter( ti ); } void * _internal_get_untyped_deleter() const BOOST_NOEXCEPT { return pn.get_untyped_deleter(); } bool _internal_equiv( shared_ptr const & r ) const BOOST_NOEXCEPT { return px == r.px && pn == r.pn; } // 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 //shared_ptr仅有的两个数据成员,一个指针,一个引用指针的个数 element_type * px; // contained pointer boost::detail::shared_count pn; // reference counter }; // shared_ptr //重载等号和不等号运算符 template<class T, class U> inline bool operator==(shared_ptr<T> const & a, shared_ptr<U> const & b) BOOST_NOEXCEPT { return a.get() == b.get(); } template<class T, class U> inline bool operator!=(shared_ptr<T> const & a, shared_ptr<U> const & b) BOOST_NOEXCEPT { 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) BOOST_NOEXCEPT { return a.get() != b.get(); } #endif #if !defined( BOOST_NO_CXX11_NULLPTR ) template<class T> inline bool operator==( shared_ptr<T> const & p, boost::detail::sp_nullptr_t ) BOOST_NOEXCEPT { return p.get() == 0; } template<class T> inline bool operator==( boost::detail::sp_nullptr_t, shared_ptr<T> const & p ) BOOST_NOEXCEPT { return p.get() == 0; } template<class T> inline bool operator!=( shared_ptr<T> const & p, boost::detail::sp_nullptr_t ) BOOST_NOEXCEPT { return p.get() != 0; } template<class T> inline bool operator!=( boost::detail::sp_nullptr_t, shared_ptr<T> const & p ) BOOST_NOEXCEPT { return p.get() != 0; } #endif //重载<比較运算符,能够用于关联容器set和map template<class T, class U> inline bool operator<(shared_ptr<T> const & a, shared_ptr<U> const & b) BOOST_NOEXCEPT { return a.owner_before( b ); } template<class T> inline void swap(shared_ptr<T> & a, shared_ptr<T> & b) BOOST_NOEXCEPT { a.swap(b); } //指针转换是,不要用C++的static_cast、const_cast,这将造成shared_ptr无法管理 //使用以下的函数来转换。它们还返回shared_ptr<T>类型 template<class T, class U> shared_ptr<T> static_pointer_cast( shared_ptr<U> const & r ) BOOST_NOEXCEPT { (void) static_cast< T* >( static_cast< U* >( 0 ) ); typedef typename shared_ptr<T>::element_type E; E * p = static_cast< E* >( r.get() ); return shared_ptr<T>( r, p ); } template<class T, class U> shared_ptr<T> const_pointer_cast( shared_ptr<U> const & r ) BOOST_NOEXCEPT { (void) const_cast< T* >( static_cast< U* >( 0 ) ); typedef typename shared_ptr<T>::element_type E; E * p = const_cast< E* >( r.get() ); return shared_ptr<T>( r, p ); } template<class T, class U> shared_ptr<T> dynamic_pointer_cast( shared_ptr<U> const & r ) BOOST_NOEXCEPT { (void) dynamic_cast< T* >( static_cast< U* >( 0 ) ); typedef typename shared_ptr<T>::element_type E; E * p = dynamic_cast< E* >( r.get() ); return p? shared_ptr<T>( r, p ): shared_ptr<T>(); } template<class T, class U> shared_ptr<T> reinterpret_pointer_cast( shared_ptr<U> const & r ) BOOST_NOEXCEPT { (void) reinterpret_cast< T* >( static_cast< U* >( 0 ) ); typedef typename shared_ptr<T>::element_type E; E * p = reinterpret_cast< E* >( r.get() ); return shared_ptr<T>( r, p ); } // get_pointer() enables boost::mem_fn to recognize shared_ptr template<class T> inline typename shared_ptr<T>::element_type * get_pointer(shared_ptr<T> const & p) BOOST_NOEXCEPT { return p.get(); } // operator<< #if !defined(BOOST_NO_IOSTREAM) #if defined(BOOST_NO_TEMPLATED_IOSTREAMS) || ( defined(__GNUC__) && (__GNUC__ < 3) ) template<class Y> std::ostream & operator<< (std::ostream & os, shared_ptr<Y> const & p) { os << p.get(); return os; } #else // in STLport's no-iostreams mode no iostream symbols can be used #ifndef _STLP_NO_IOSTREAMS # if defined(BOOST_MSVC) && BOOST_WORKAROUND(BOOST_MSVC, < 1300 && __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; }
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原文地址:http://www.cnblogs.com/hrhguanli/p/4807132.html