forked from boostorg/smart_ptr
225 lines
10 KiB
HTML
225 lines
10 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
|
|
|
|
<html>
|
|
|
|
<head>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
|
|
<title>shared_array</title>
|
|
</head>
|
|
|
|
<body bgcolor="#FFFFFF" text="#000000">
|
|
|
|
<h1><img src="../../c++boost.gif" alt="c++boost.gif (8819 bytes)" align="middle" width="277" height="86">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 a
|
|
single dynamically allocated object. See <a href="shared_ptr.htm"><b>shared_ptr</b></a>
|
|
for that usage.</p>
|
|
|
|
<p>Because the implementation uses reference counting, <b>shared_array</b> will not work
|
|
correctly with cyclic data structures. 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<typename 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<typename 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<typename D> void <a href="#reset">reset</a>(T * p, D d);
|
|
|
|
T & <a href="#indexing">operator[]</a>(std::ptrdiff_t i) const() 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
|
|
|
|
void <a href="#swap">swap</a>(shared_array<T> & b); // never throws
|
|
};
|
|
|
|
template<typename T>
|
|
bool <a href="#comparison">operator==</a>(shared_array<T> const & a, shared_array<T> const & b); // never throws
|
|
template<typename T>
|
|
bool <a href="#comparison">operator!=</a>(shared_array<T> const & a, shared_array<T> const & b); // never throws
|
|
template<typename T>
|
|
bool <a href="#comparison">operator<</a>(shared_array<T> const & a, shared_array<T> const & b); // never throws
|
|
|
|
template<typename 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<typename 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="operator=">assignment</a></h3>
|
|
|
|
<pre>shared_array & <a href="#assignment">operator=</a>(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<typename 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="indirection">indexing</a></h3>
|
|
<pre>T & operator[](std::size_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="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<typename T>
|
|
bool operator==(shared_array<T> const & a, shared_array<T> const & b); // never throws
|
|
template<typename T>
|
|
bool operator!=(shared_array<T> const & a, shared_array<T> const & b); // never throws
|
|
template<typename 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<typename 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 -->8 February 2002<!--webbot bot="Timestamp" i-checksum="38439" endspan --></p>
|
|
|
|
<p>Copyright 1999 Greg Colvin and Beman Dawes. Copyright 2002 Darin Adler.
|
|
Permission to copy, use, modify, sell and distribute this document is granted
|
|
provided this copyright notice appears in all copies.
|
|
This document is provided "as is" without express or implied warranty,
|
|
and with no claim as to its suitability for any purpose.</p>
|
|
|
|
</body>
|
|
|
|
</html>
|