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| <h1><A href="../../index.htm"><img src="../../boost.png" alt="boost.png (6897 bytes)" align="middle" width="277" height="86" |
| border="0"></A>shared_array class template</h1> |
| <p>The <b>shared_array</b> class template stores a pointer to a dynamically |
| allocated array. (Dynamically allocated array are allocated with the C++ <b>new[]</b> |
| expression.) The object pointed to is guaranteed to be deleted when the last <b>shared_array</b> |
| pointing to it is destroyed or reset.</p> |
| <p>Every <b>shared_array</b> meets the <b>CopyConstructible</b> and <b>Assignable</b> |
| requirements of the C++ Standard Library, and so can be used in standard |
| library containers. Comparison operators are supplied so that <b>shared_array</b> |
| works with the standard library's associative containers.</p> |
| <p>Normally, a <b>shared_array</b> cannot correctly hold a pointer to an object |
| that has been allocated with the non-array form of <STRONG>new</STRONG>. See <a href="shared_ptr.htm"> |
| <b>shared_ptr</b></a> for that usage.</p> |
| <p>Because the implementation uses reference counting, cycles of <b>shared_array</b> |
| instances will not be reclaimed. For example, if <b>main()</b> holds a <b>shared_array</b> |
| to <b>A</b>, which directly or indirectly holds a <b>shared_array</b> back to <b>A</b>, |
| <b>A</b>'s use count will be 2. Destruction of the original <b>shared_array</b> |
| will leave <b>A</b> dangling with a use count of 1.</p> |
| <p>A <b>shared_ptr</b> to a <b>std::vector</b> is an alternative to a <b>shared_array</b> |
| that is a bit heavier duty but far more flexible.</p> |
| <p>The class template is parameterized on <b>T</b>, the type of the object pointed |
| to. <b>T</b> must meet the smart pointer <a href="smart_ptr.htm#common_requirements"> |
| common requirements</a>.</p> |
| <h2>Synopsis</h2> |
| <pre>namespace boost { |
| |
| template<class T> class shared_array { |
| |
| public: |
| typedef T <a href="#element_type">element_type</a>; |
| |
| explicit <a href="#constructors">shared_array</a>(T * p = 0); |
| template<class D> <a href="#constructors">shared_array</a>(T * p, D d); |
| <a href="#destructor">~shared_array</a>(); // never throws |
| |
| <a href="#constructors">shared_array</a>(shared_array const & r); // never throws |
| |
| shared_array & <a href="#assignment">operator=</a>(shared_array const & r); // never throws |
| |
| void <a href="#reset">reset</a>(T * p = 0); |
| template<class D> void <a href="#reset">reset</a>(T * p, D d); |
| |
| T & <a href="#indexing">operator[]</a>(std::ptrdiff_t i) const; // never throws |
| T * <a href="#get">get</a>() const; // never throws |
| |
| bool <a href="#unique">unique</a>() const; // never throws |
| long <a href="#use_count">use_count</a>() const; // never throws |
| |
| operator <A href="#conversions" ><i>unspecified-bool-type</i></A>() const; // never throws |
| |
| void <a href="#swap">swap</a>(shared_array<T> & b); // never throws |
| }; |
| |
| template<class T> |
| bool <a href="#comparison">operator==</a>(shared_array<T> const & a, shared_array<T> const & b); // never throws |
| template<class T> |
| bool <a href="#comparison">operator!=</a>(shared_array<T> const & a, shared_array<T> const & b); // never throws |
| template<class T> |
| bool <a href="#comparison">operator<</a>(shared_array<T> const & a, shared_array<T> const & b); // never throws |
| |
| template<class T> void <a href="#free-swap">swap</a>(shared_array<T> & a, shared_array<T> & b); // never throws |
| |
| }</pre> |
| <h2>Members</h2> |
| <h3><a name="element_type">element_type</a></h3> |
| <pre>typedef T element_type;</pre> |
| <p>Provides the type of the stored pointer.</p> |
| <h3><a name="constructors">constructors</a></h3> |
| <pre>explicit shared_array(T * p = 0);</pre> |
| <p>Constructs a <b>shared_array</b>, storing a copy of <b>p</b>, which must be a |
| pointer to an array that was allocated via a C++ <b>new[]</b> expression or be |
| 0. Afterwards, the <a href="#use_count">use count</a> is 1 (even if p == 0; see <a href="#destructor"> |
| ~shared_array</a>). The only exception which may be thrown by this |
| constructor is <b>std::bad_alloc</b>. If an exception is thrown, <b>delete[] p</b> |
| is called.</p> |
| <pre>template<class D> shared_array(T * p, D d);</pre> |
| <p>Constructs a <b>shared_array</b>, storing a copy of <b>p</b> and of <b>d</b>. |
| Afterwards, the <a href="#use_count">use count</a> is 1. <b>D</b>'s copy |
| constructor and destructor must not throw. When the the time comes to delete |
| the array pointed to by <b>p</b>, the object <b>d</b> is used in the statement <b>d(p)</b>. |
| Invoking the object <b>d</b> with parameter <b>p</b> in this way must not |
| throw. The only exception which may be thrown by this constructor is <b>std::bad_alloc</b>. |
| If an exception is thrown, <b>d(p)</b> is called.</p> |
| <pre>shared_array(shared_array const & r); // never throws</pre> |
| <p>Constructs a <b>shared_array</b>, as if by storing a copy of the pointer stored |
| in <b>r</b>. Afterwards, the <a href="#use_count">use count</a> for all copies |
| is 1 more than the initial use count.</p> |
| <h3><a name="destructor">destructor</a></h3> |
| <pre>~shared_array(); // never throws</pre> |
| <p>Decrements the <a href="#use_count">use count</a>. Then, if the use count is 0, |
| deletes the array pointed to by the stored pointer. Note that <b>delete[]</b> on |
| a pointer with a value of 0 is harmless. <b>T</b> need not be a complete type. |
| The guarantee that this does not throw exceptions depends on the requirement |
| that the deleted object's destructor does not throw exceptions. See the smart |
| pointer <a href="smart_ptr.htm#common_requirements">common requirements</a>.</p> |
| <h3><a name="assignment">assignment</a></h3> |
| <pre>shared_array & operator=(shared_array const & r); // never throws</pre> |
| <p>Constructs a new <b>shared_array</b> as described <a href="#constructors">above</a>, |
| then replaces this <b>shared_array</b> with the new one, destroying the |
| replaced object.</p> |
| <h3><a name="reset">reset</a></h3> |
| <pre>void reset(T * p = 0);</pre> |
| <p>Constructs a new <b>shared_array</b> as described <a href="#constructors">above</a>, |
| then replaces this <b>shared_array</b> with the new one, destroying the |
| replaced object. The only exception which may be thrown is <b>std::bad_alloc</b>. |
| If an exception is thrown, <b>delete[] p</b> is called.</p> |
| <pre>template<class D> void reset(T * p, D d);</pre> |
| <p>Constructs a new <b>shared_array</b> as described <a href="#constructors">above</a>, |
| then replaces this <b>shared_array</b> with the new one, destroying the |
| replaced object. <b>D</b>'s copy constructor must not throw. The only exception |
| which may be thrown is <b>std::bad_alloc</b>. If an exception is thrown, <b>d(p)</b> |
| is called.</p> |
| <h3><a name="indexing">indexing</a></h3> |
| <pre>T & operator[](std::ptrdiff_t i) const; // never throws</pre> |
| <p>Returns a reference to element <b>i</b> of the array pointed to by the stored |
| pointer. Behavior is undefined and almost certainly undesirable if the stored |
| pointer is 0, or if <b>i</b> is less than 0 or is greater than or equal to the |
| number of elements in the array.</p> |
| <h3><a name="get">get</a></h3> |
| <pre>T * get() const; // never throws</pre> |
| <p>Returns the stored pointer. <b>T</b> need not be a complete type. See the smart |
| pointer <a href="smart_ptr.htm#common_requirements">common requirements</a>.</p> |
| <h3><a name="unique">unique</a></h3> |
| <pre>bool unique() const; // never throws</pre> |
| <p>Returns true if no other <b>shared_array</b> is sharing ownership of the stored |
| pointer, false otherwise. <b>T</b> need not be a complete type. See the smart |
| pointer <a href="smart_ptr.htm#common_requirements">common requirements</a>.</p> |
| <h3><a name="use_count">use_count</a></h3> |
| <pre>long use_count() const; // never throws</pre> |
| <p>Returns the number of <b>shared_array</b> objects sharing ownership of the |
| stored pointer. <b>T</b> need not be a complete type. See the smart pointer <a href="smart_ptr.htm#common_requirements"> |
| common requirements</a>.</p> |
| <p>Because <b>use_count</b> is not necessarily efficient to implement for |
| implementations of <b>shared_array</b> that do not use an explicit reference |
| count, it might be removed from some future version. Thus it should be used for |
| debugging purposes only, and not production code.</p> |
| <h3><a name="conversions">conversions</a></h3> |
| <pre>operator <i>unspecified-bool-type</i> () const; // never throws</pre> |
| <p>Returns an unspecified value that, when used in boolean contexts, is equivalent |
| to <code>get() != 0</code>.</p> |
| <h3><a name="swap">swap</a></h3> |
| <pre>void swap(shared_ptr & b); // never throws</pre> |
| <p>Exchanges the contents of the two smart pointers. <b>T</b> need not be a |
| complete type. See the smart pointer <a href="smart_ptr.htm#common_requirements">common |
| requirements</a>.</p> |
| <h2><a name="functions">Free Functions</a></h2> |
| <h3><a name="comparison">comparison</a></h3> |
| <pre>template<class T> |
| bool operator==(shared_array<T> const & a, shared_array<T> const & b); // never throws |
| template<class T> |
| bool operator!=(shared_array<T> const & a, shared_array<T> const & b); // never throws |
| template<class T> |
| bool operator<(shared_array<T> const & a, shared_array<T> const & b); // never throws</pre> |
| <p>Compares the stored pointers of the two smart pointers. <b>T</b> need not be a |
| complete type. See the smart pointer <a href="smart_ptr.htm#common_requirements">common |
| requirements</a>.</p> |
| <p>The <b>operator<</b> overload is provided to define an ordering so that <b>shared_array</b> |
| objects can be used in associative containers such as <b>std::map</b>. The |
| implementation uses <b>std::less<T *></b> to perform the comparison. This |
| ensures that the comparison is handled correctly, since the standard mandates |
| that relational operations on pointers are unspecified (5.9 [expr.rel] |
| paragraph 2) but <b>std::less<></b> on pointers is well-defined (20.3.3 |
| [lib.comparisons] paragraph 8).</p> |
| <h3><a name="free-swap">swap</a></h3> |
| <pre>template<class T> |
| void swap(shared_array<T> & a, shared_array<T> & b) // never throws</pre> |
| <p>Equivalent to <b>a.swap(b)</b>. Matches the interface of <b>std::swap</b>. |
| Provided as an aid to generic programming.</p> |
| <hr> |
| <p>Revised |
| <!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B %Y" startspan --> |
| 09 January 2003<!--webbot bot="Timestamp" endspan i-checksum="32310" --></p> |
| <p><small>Copyright 1999 Greg Colvin and Beman Dawes. Copyright 2002 Darin Adler. |
| Copyright 2002-2005 Peter Dimov. Distributed under the Boost Software License, Version |
| 1.0. See accompanying file <A href="../../LICENSE_1_0.txt">LICENSE_1_0.txt</A> or |
| copy at <A href="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</A>.</small></p> |
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