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| 4 | <title>shared_array</title> |
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| 8 | <h1><img src="../../boost.png" alt="boost.png (6897 bytes)" align="middle" width="277" height="86">shared_array |
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| 9 | class template</h1> |
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| 10 | <p>The <b>shared_array</b> class template stores a pointer to a dynamically |
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| 11 | allocated array. (Dynamically allocated array are allocated with the C++ <b>new[]</b> |
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| 12 | expression.) The object pointed to is guaranteed to be deleted when the last <b>shared_array</b> |
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| 13 | pointing to it is destroyed or reset.</p> |
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| 14 | <p>Every <b>shared_array</b> meets the <b>CopyConstructible</b> and <b>Assignable</b> |
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| 15 | requirements of the C++ Standard Library, and so can be used in standard |
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| 16 | library containers. Comparison operators are supplied so that <b>shared_array</b> |
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| 17 | works with the standard library's associative containers.</p> |
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| 18 | <p>Normally, a <b>shared_array</b> cannot correctly hold a pointer to an object |
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| 19 | that has been allocated with the non-array form of <STRONG>new</STRONG>. See <a href="shared_ptr.htm"> |
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| 20 | <b>shared_ptr</b></a> for that usage.</p> |
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| 21 | <p>Because the implementation uses reference counting, cycles of <b>shared_array</b> |
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| 22 | instances will not be reclaimed. For example, if <b>main()</b> holds a <b>shared_array</b> |
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| 23 | to <b>A</b>, which directly or indirectly holds a <b>shared_array</b> back to <b>A</b>, |
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| 24 | <b>A</b>'s use count will be 2. Destruction of the original <b>shared_array</b> |
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| 25 | will leave <b>A</b> dangling with a use count of 1.</p> |
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| 26 | <p>A <b>shared_ptr</b> to a <b>std::vector</b> is an alternative to a <b>shared_array</b> |
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| 27 | that is a bit heavier duty but far more flexible.</p> |
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| 28 | <p>The class template is parameterized on <b>T</b>, the type of the object pointed |
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| 29 | to. <b>T</b> must meet the smart pointer <a href="smart_ptr.htm#common_requirements"> |
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| 30 | common requirements</a>.</p> |
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| 31 | <h2>Synopsis</h2> |
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| 32 | <pre>namespace boost { |
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| 33 | |
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| 34 | template<class T> class shared_array { |
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| 35 | |
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| 36 | public: |
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| 37 | typedef T <a href="#element_type">element_type</a>; |
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| 38 | |
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| 39 | explicit <a href="#constructors">shared_array</a>(T * p = 0); |
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| 40 | template<class D> <a href="#constructors">shared_array</a>(T * p, D d); |
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| 41 | <a href="#destructor">~shared_array</a>(); // never throws |
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| 42 | |
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| 43 | <a href="#constructors">shared_array</a>(shared_array const & r); // never throws |
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| 44 | |
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| 45 | shared_array & <a href="#assignment">operator=</a>(shared_array const & r); // never throws |
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| 46 | |
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| 47 | void <a href="#reset">reset</a>(T * p = 0); |
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| 48 | template<class D> void <a href="#reset">reset</a>(T * p, D d); |
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| 49 | |
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| 50 | T & <a href="#indexing">operator[]</a>(std::ptrdiff_t i) const() const; // never throws |
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| 51 | T * <a href="#get">get</a>() const; // never throws |
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| 52 | |
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| 53 | bool <a href="#unique">unique</a>() const; // never throws |
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| 54 | long <a href="#use_count">use_count</a>() const; // never throws |
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| 55 | |
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| 56 | void <a href="#swap">swap</a>(shared_array<T> & b); // never throws |
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| 57 | }; |
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| 58 | |
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| 59 | template<class T> |
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| 60 | bool <a href="#comparison">operator==</a>(shared_array<T> const & a, shared_array<T> const & b); // never throws |
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| 61 | template<class T> |
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| 62 | bool <a href="#comparison">operator!=</a>(shared_array<T> const & a, shared_array<T> const & b); // never throws |
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| 63 | template<class T> |
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| 64 | bool <a href="#comparison">operator<</a>(shared_array<T> const & a, shared_array<T> const & b); // never throws |
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| 65 | |
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| 66 | template<class T> void <a href="#free-swap">swap</a>(shared_array<T> & a, shared_array<T> & b); // never throws |
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| 67 | |
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| 68 | }</pre> |
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| 69 | <h2>Members</h2> |
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| 70 | <h3><a name="element_type">element_type</a></h3> |
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| 71 | <pre>typedef T element_type;</pre> |
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| 72 | <p>Provides the type of the stored pointer.</p> |
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| 73 | <h3><a name="constructors">constructors</a></h3> |
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| 74 | <pre>explicit shared_array(T * p = 0);</pre> |
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| 75 | <p>Constructs a <b>shared_array</b>, storing a copy of <b>p</b>, which must be a |
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| 76 | pointer to an array that was allocated via a C++ <b>new[]</b> expression or be |
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| 77 | 0. Afterwards, the <a href="#use_count">use count</a> is 1 (even if p == 0; see <a href="#destructor"> |
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| 78 | ~shared_array</a>). The only exception which may be thrown by this |
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| 79 | constructor is <b>std::bad_alloc</b>. If an exception is thrown, <b>delete[] p</b> |
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| 80 | is called.</p> |
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| 81 | <pre>template<class D> shared_array(T * p, D d);</pre> |
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| 82 | <p>Constructs a <b>shared_array</b>, storing a copy of <b>p</b> and of <b>d</b>. |
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| 83 | Afterwards, the <a href="#use_count">use count</a> is 1. <b>D</b>'s copy |
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| 84 | constructor and destructor must not throw. When the the time comes to delete |
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| 85 | the array pointed to by <b>p</b>, the object <b>d</b> is used in the statement <b>d(p)</b>. |
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| 86 | Invoking the object <b>d</b> with parameter <b>p</b> in this way must not |
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| 87 | throw. The only exception which may be thrown by this constructor is <b>std::bad_alloc</b>. |
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| 88 | If an exception is thrown, <b>d(p)</b> is called.</p> |
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| 89 | <pre>shared_array(shared_array const & r); // never throws</pre> |
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| 90 | <p>Constructs a <b>shared_array</b>, as if by storing a copy of the pointer stored |
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| 91 | in <b>r</b>. Afterwards, the <a href="#use_count">use count</a> for all copies |
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| 92 | is 1 more than the initial use count.</p> |
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| 93 | <h3><a name="destructor">destructor</a></h3> |
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| 94 | <pre>~shared_array(); // never throws</pre> |
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| 95 | <p>Decrements the <a href="#use_count">use count</a>. Then, if the use count is 0, |
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| 96 | deletes the array pointed to by the stored pointer. Note that <b>delete[]</b> on |
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| 97 | a pointer with a value of 0 is harmless. <b>T</b> need not be a complete type. |
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| 98 | The guarantee that this does not throw exceptions depends on the requirement |
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| 99 | that the deleted object's destructor does not throw exceptions. See the smart |
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| 100 | pointer <a href="smart_ptr.htm#common_requirements">common requirements</a>.</p> |
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| 101 | <h3><a name="assignment">assignment</a></h3> |
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| 102 | <pre>shared_array & operator=(shared_array const & r); // never throws</pre> |
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| 103 | <p>Constructs a new <b>shared_array</b> as described <a href="#constructors">above</a>, |
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| 104 | then replaces this <b>shared_array</b> with the new one, destroying the |
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| 105 | replaced object.</p> |
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| 106 | <h3><a name="reset">reset</a></h3> |
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| 107 | <pre>void reset(T * p = 0);</pre> |
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| 108 | <p>Constructs a new <b>shared_array</b> as described <a href="#constructors">above</a>, |
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| 109 | then replaces this <b>shared_array</b> with the new one, destroying the |
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| 110 | replaced object. The only exception which may be thrown is <b>std::bad_alloc</b>. |
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| 111 | If an exception is thrown, <b>delete[] p</b> is called.</p> |
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| 112 | <pre>template<class D> void reset(T * p, D d);</pre> |
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| 113 | <p>Constructs a new <b>shared_array</b> as described <a href="#constructors">above</a>, |
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| 114 | then replaces this <b>shared_array</b> with the new one, destroying the |
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| 115 | replaced object. <b>D</b>'s copy constructor must not throw. The only exception |
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| 116 | which may be thrown is <b>std::bad_alloc</b>. If an exception is thrown, <b>d(p)</b> |
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| 117 | is called.</p> |
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| 118 | <h3><a name="indexing">indexing</a></h3> |
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| 119 | <pre>T & operator[](std::ptrdiff_t i) const; // never throws</pre> |
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| 120 | <p>Returns a reference to element <b>i</b> of the array pointed to by the stored |
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| 121 | pointer. Behavior is undefined and almost certainly undesirable if the stored |
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| 122 | pointer is 0, or if <b>i</b> is less than 0 or is greater than or equal to the |
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| 123 | number of elements in the array.</p> |
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| 124 | <h3><a name="get">get</a></h3> |
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| 125 | <pre>T * get() const; // never throws</pre> |
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| 126 | <p>Returns the stored pointer. <b>T</b> need not be a complete type. See the smart |
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| 127 | pointer <a href="smart_ptr.htm#common_requirements">common requirements</a>.</p> |
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| 128 | <h3><a name="unique">unique</a></h3> |
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| 129 | <pre>bool unique() const; // never throws</pre> |
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| 130 | <p>Returns true if no other <b>shared_array</b> is sharing ownership of the stored |
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| 131 | pointer, false otherwise. <b>T</b> need not be a complete type. See the smart |
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| 132 | pointer <a href="smart_ptr.htm#common_requirements">common requirements</a>.</p> |
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| 133 | <h3><a name="use_count">use_count</a></h3> |
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| 134 | <pre>long use_count() const; // never throws</pre> |
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| 135 | <p>Returns the number of <b>shared_array</b> objects sharing ownership of the |
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| 136 | stored pointer. <b>T</b> need not be a complete type. See the smart pointer <a href="smart_ptr.htm#common_requirements"> |
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| 137 | common requirements</a>.</p> |
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| 138 | <p>Because <b>use_count</b> is not necessarily efficient to implement for |
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| 139 | implementations of <b>shared_array</b> that do not use an explicit reference |
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| 140 | count, it might be removed from some future version. Thus it should be used for |
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| 141 | debugging purposes only, and not production code.</p> |
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| 142 | <h3><a name="swap">swap</a></h3> |
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| 143 | <pre>void swap(shared_ptr & b); // never throws</pre> |
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| 144 | <p>Exchanges the contents of the two smart pointers. <b>T</b> need not be a |
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| 145 | complete type. See the smart pointer <a href="smart_ptr.htm#common_requirements">common |
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| 146 | requirements</a>.</p> |
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| 147 | <h2><a name="functions">Free Functions</a></h2> |
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| 148 | <h3><a name="comparison">comparison</a></h3> |
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| 149 | <pre>template<class T> |
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| 150 | bool operator==(shared_array<T> const & a, shared_array<T> const & b); // never throws |
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| 151 | template<class T> |
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| 152 | bool operator!=(shared_array<T> const & a, shared_array<T> const & b); // never throws |
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| 153 | template<class T> |
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| 154 | bool operator<(shared_array<T> const & a, shared_array<T> const & b); // never throws</pre> |
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| 155 | <p>Compares the stored pointers of the two smart pointers. <b>T</b> need not be a |
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| 156 | complete type. See the smart pointer <a href="smart_ptr.htm#common_requirements">common |
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| 157 | requirements</a>.</p> |
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| 158 | <p>The <b>operator<</b> overload is provided to define an ordering so that <b>shared_array</b> |
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| 159 | objects can be used in associative containers such as <b>std::map</b>. The |
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| 160 | implementation uses <b>std::less<T *></b> to perform the comparison. This |
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| 161 | ensures that the comparison is handled correctly, since the standard mandates |
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| 162 | that relational operations on pointers are unspecified (5.9 [expr.rel] |
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| 163 | paragraph 2) but <b>std::less<></b> on pointers is well-defined (20.3.3 |
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| 164 | [lib.comparisons] paragraph 8).</p> |
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| 165 | <h3><a name="free-swap">swap</a></h3> |
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| 166 | <pre>template<class T> |
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| 167 | void swap(shared_array<T> & a, shared_array<T> & b) // never throws</pre> |
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| 168 | <p>Equivalent to <b>a.swap(b)</b>. Matches the interface of <b>std::swap</b>. |
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| 169 | Provided as an aid to generic programming.</p> |
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| 170 | <hr> |
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| 171 | <p>Revised |
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| 172 | <!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B %Y" startspan --> |
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| 173 | 09 January 2003<!--webbot bot="Timestamp" endspan i-checksum="32310" --></p> |
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| 174 | <p>Copyright 1999 Greg Colvin and Beman Dawes. Copyright 2002 Darin Adler. |
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| 175 | Permission to copy, use, modify, sell and distribute this document is granted |
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| 176 | provided this copyright notice appears in all copies. This document is provided |
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| 177 | "as is" without express or implied warranty, and with no claim as to its |
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| 178 | suitability for any purpose.</p> |
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| 179 | </body> |
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| 180 | </html> |
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