forked from boostorg/smart_ptr
Update make shared for arrays documentation
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Glen Fernandes
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<title>make_shared and allocate_shared</title>
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<title>make_shared and allocate_shared for arrays</title>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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</head>
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<body text="#000000" bgColor="#ffffff" link="#0000ff" vlink="#0000ff">
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<body text="#000000" bgcolor="#ffffff" link="#0000ff" vlink="#0000ff">
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<h1><img height="86" alt="boost.png (6897 bytes)" src="../../boost.png"
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width="277" align="middle" border="0">make_shared and allocate_shared
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for arrays</h1>
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<p><A href="#Introduction">Introduction</A><br>
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<A href="#Synopsis">Synopsis</A><br>
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<A href="#functions">Free Functions</A><br>
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<A href="#example">Example</A><br>
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<A href="#history">History</A><br></p>
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<p><a href="#Introduction">Introduction</a><br>
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<a href="#Synopsis">Synopsis</a><br>
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<a href="#functions">Free Functions</a><br>
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<a href="#example">Examples</a><br>
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<a href="#history">History</a><br>
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<a href="#references">References</a></p>
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<h2><a name="Introduction">Introduction</a></h2>
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<p>Originally the Boost function templates <code>make_shared</code> and
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<code>allocate_shared</code> were for efficient allocation of single
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objects only. There was a need to have efficient, single, allocation of
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arrays. One criticism of <a href="shared_array.htm">shared_array</a> was
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always the lack of a <a href="make_shared.html">make_shared</a> utility
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which ensures only a single allocation for an array.</p>
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<code>allocate_shared</code> were for efficient allocation of shared
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objects only. There was a need to have efficient allocation of
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shared arrays. One criticism of class template <code>shared_array</code>
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was always the lack of a <a href="make_shared.html">make_shared</a>
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utility which ensures only a single allocation.</p>
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<p>The header files <boost/smart_ptr/make_shared_array.hpp> and
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<boost/smart_ptr/allocate_shared_array.hpp> provide new function
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templates, <code>make_shared</code> and <code>allocate_shared</code>,
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to address this need. <code>make_shared</code> uses the global
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operator <code>new</code> to allocate memory, whereas
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<code>allocate_shared</code> uses an user-supplied allocator,
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allowing finer control.</p>
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<boost/smart_ptr/allocate_shared_array.hpp> provide function
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templates, overloads of <code>make_shared</code> and
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<code>allocate_shared</code> for array types, to address this need.
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<code>make_shared</code> uses the global operator <code>new</code> to
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allocate memory, whereas <code>allocate_shared</code> uses an
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user-supplied allocator, allowing finer control.</p>
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<h2><a name="Synopsis">Synopsis</a></h2>
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<pre>namespace boost {
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template<typename U> // U is T[]
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@ -80,18 +81,17 @@ shared_ptr<U> allocate_shared(const A& allocator);</pre>
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<blockquote>
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<p><b>Requires:</b> The expression
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<code>new(pointer) T()</code>, where <code>pointer</code> is a
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<code>void*</code> pointing to storage suitable to hold an object
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of type <code>T</code>, shall be well-formed. <code>A</code>
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shall be an <em>Allocator</em>, as described in section 20.1.5
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(<strong>Allocator requirements</strong>) of the C++ Standard.
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The copy constructor and destructor of <code>A</code> shall not
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throw.</p>
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<code>void*</code> pointing to storage suitable to hold an object of
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type <code>T</code>, shall be well-formed. <code>A</code> shall be an
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<em>Allocator</em>, as described in section 20.1.5 (<strong>Allocator
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requirements</strong>) of the C++ Standard. The copy constructor and
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destructor of <code>A</code> shall not throw.</p>
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<p><b>Effects:</b> Allocates memory suitable for an array of type
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<code>T</code> and size <code>size</code> and constructs an array
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of objects in it via the placement new expression
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<code>new(pointer) T()</code>. <code>allocate_shared</code> uses
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a copy of <code>allocator</code> to allocate memory. If an
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exception is thrown, has no effect.</p>
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<code>T</code> and size <code>size</code> and constructs an array of
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objects in it via the placement new expression <code>new(pointer)
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T()</code>. <code>allocate_shared</code> uses a copy of
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<code>allocator</code> to allocate memory. If an exception is thrown,
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has no effect.</p>
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<p><b>Returns:</b> A <code>shared_ptr</code> instance that stores and
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owns the address of the newly constructed array of type <code>T</code>
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and size <code>size</code>.</p>
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@ -102,8 +102,7 @@ shared_ptr<U> allocate_shared(const A& allocator);</pre>
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<p><b>Notes:</b> This implementation allocates the memory required for
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the returned <code>shared_ptr</code> and an array of type
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<code>T</code> of size <code>size</code> in a single allocation. This
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provides efficiency to equivalent to an intrusive smart array
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pointer.</p>
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provides efficiency to equivalent to an intrusive smart pointer.</p>
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</blockquote>
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<pre>template<typename U> // U is T[]
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shared_ptr<U> make_shared(size_t size, const T& value);
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@ -117,8 +116,8 @@ shared_ptr<U> make_shared(const T& value);
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template<typename U, typename A> // U is T[N]
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shared_ptr<U> allocate_shared(const A& allocator, const T& value);</pre>
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<blockquote>
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<p><b>Description:</b> These overloads initialize array elements with
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the given value.</p>
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<p><b>Notes:</b> These overloads initialize array objects with the given
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value.</p>
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</blockquote>
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<pre>template<typename U> // U is T[]
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shared_ptr<U> make_shared_noinit(size_t size);
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@ -132,28 +131,41 @@ shared_ptr<U> make_shared_noinit();
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template<typename U, typename A> // U is T[N]
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shared_ptr<U> allocate_shared_noinit(const A& allocator);</pre>
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<blockquote>
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<p><b>Description:</b> These overloads do not perform any value
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initialization of elements.</p>
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<p><b>Notes:</b> These overloads do not perform value initialization of
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array objects.</p>
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</blockquote>
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<h2><a name="example">Examples</a></h2>
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<p>Some examples of each overload of make_shared for arrays:</p>
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<p>The following examples value-initialize objects.</p>
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<blockquote>
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<pre>boost::shared_ptr<int[]> a1 = boost::make_shared<int[]>(size);
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boost::shared_ptr<int[8]> a2 = boost::make_shared<int[8]>();
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boost::shared_ptr<int[][2]> a3 = boost::make_shared<int[][2]>(size);
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boost::shared_ptr<int[4][2]> a4 = boost::make_shared<int[4][2]>();
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boost::shared_ptr<int[]> a5 = boost::make_shared<int[]>(size, 1);
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boost::shared_ptr<int[8]> a6 = boost::make_shared<int[8]>(1);
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boost::shared_ptr<int[][2]> a7 = boost::make_shared<int[][2]>(size, {1, 2});
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boost::shared_ptr<int[4][2]> a8 = boost::make_shared<int[4][2]>({1, 2});
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boost::shared_ptr<int[]> a9 = boost::make_shared_noinit<int[]>(size);
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boost::shared_ptr<int[8]> a10 = boost::make_shared_noinit<int[8]>();
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boost::shared_ptr<int[][2]> a11 = boost::make_shared_noinit<int[][2]>(size);
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<pre>boost::shared_ptr<int[]> a1 = boost::make_shared<int[]>(size);
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boost::shared_ptr<int[8]> a2 = boost::make_shared<int[8]>();
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boost::shared_ptr<int[][2]> a3 = boost::make_shared<int[][2]>(size);
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boost::shared_ptr<int[4][2]> a4 = boost::make_shared<int[4][2]>();</pre>
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</blockquote>
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<p>The following examples initialize objects with a given value.</p>
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<blockquote>
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<pre>boost::shared_ptr<int[]> a5 = boost::make_shared<int[]>(size, 1);
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boost::shared_ptr<int[8]> a6 = boost::make_shared<int[8]>(1);
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boost::shared_ptr<int[][2]> a7 = boost::make_shared<int[][2]>(size, {1, 2});
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boost::shared_ptr<int[4][2]> a8 = boost::make_shared<int[4][2]>({1, 2});</pre>
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</blockquote>
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<p>The following examples default-initialize objects.</p>
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<blockquote>
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<pre>boost::shared_ptr<int[]> a9 = boost::make_shared_noinit<int[]>(size);
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boost::shared_ptr<int[8]> a10 = boost::make_shared_noinit<int[8]>();
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boost::shared_ptr<int[][2]> a11 = boost::make_shared_noinit<int[][2]>(size);
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boost::shared_ptr<int[4][2]> a12 = boost::make_shared_noinit<int[4][2]>();</pre>
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</blockquote>
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<h2><a name="history">History</a></h2>
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<p>January 2014. Glen Fernandes reduced the overloads of make_shared and
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allocate_shared according to <a href="#N3870">N3870</a>.</p>
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<p>November 2012. Glen Fernandes contributed implementations of
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make_shared and allocate_shared for arrays.</p>
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<h2><a name="references">References</a></h2>
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<p><a name="N3870">N3870</a>,
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<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3870.html">
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Extending make_shared to Support Arrays, Revision 1</a>, Peter Dimov
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& Glen Fernandes, January, 2014.</p>
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<hr>
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<p>$Date: 2014-01-20 11:10:00 -0800 (Mon, 20 Jan 2014) $</p>
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<p><small>Copyright 2012-2014 Glen Fernandes. Distributed under the
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@ -66,7 +66,7 @@
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<div align="left">
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<table border="1" cellpadding="4" cellspacing="0">
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<tr>
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<td><a href="make_shared.html"><b>make_shared and allocate_shared</b></a></td>
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<td><a href="make_shared.html"><b>make_shared and allocate_shared for objects</b></a></td>
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<td><a href="../../boost/make_shared.hpp"><boost/make_shared.hpp></a></td>
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<td>Efficient creation of <code>shared_ptr</code> objects.</td>
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</tr>
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