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<tr class="t-nv-h2"><td colspan="5"> Relational operators</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="../utility/rel_ops/operator_cmp.html" title="cpp/utility/rel ops/operator cmp"><span class="t-lines"><span>rel_ops::operator!=</span><span>rel_ops::operator></span><span>rel_ops::operator<=</span><span>rel_ops::operator>=</span></span></a></div></div></td></tr>
<tr class="t-nv-h2"><td colspan="5"> Pairs and tuples</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="../utility/pair.html" title="cpp/utility/pair"><span class="t-lines"><span>pair</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="../utility/tuple.html" title="cpp/utility/tuple"><span class="t-lines"><span>tuple</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="../utility/piecewise_construct_t.html" title="cpp/utility/piecewise construct t"><span class="t-lines"><span>piecewise_construct_t</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="../utility/piecewise_construct.html" title="cpp/utility/piecewise construct"><span class="t-lines"><span>piecewise_construct</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="../utility/integer_sequence.html" title="cpp/utility/integer sequence"><span class="t-lines"><span>integer_sequence</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx14">(C++14)</span></span></span></div></div></td></tr>
<tr class="t-nv-h2"><td colspan="5"> Swap, forward and move</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="../algorithm/swap.html" title="cpp/algorithm/swap"><span class="t-lines"><span>swap</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="../utility/exchange.html" title="cpp/utility/exchange"><span class="t-lines"><span>exchange</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx14">(C++14)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="../utility/forward.html" title="cpp/utility/forward"><span class="t-lines"><span>forward</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="../utility/move.html" title="cpp/utility/move"><span class="t-lines"><span>move</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="../utility/move_if_noexcept.html" title="cpp/utility/move if noexcept"><span class="t-lines"><span>move_if_noexcept</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv-h2"><td colspan="5"> Type operations</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="../utility/declval.html" title="cpp/utility/declval"><span class="t-lines"><span>declval</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="../utility/as_const.html" title="cpp/utility/as const"><span class="t-lines"><span>as_const</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span></span></div></div></td></tr>
</table></div><div><span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/utility/navbar_content&action=edit">[edit]</a></span></div></div></div></div><div class="t-navbar-sep"> </div><div class="t-navbar-head"><a href="../memory.html" title="cpp/memory"> Dynamic memory management</a><div class="t-navbar-menu"><div><div><table class="t-nv-begin" cellpadding="0" style="">
<tr class="t-nv-h1"><td colspan="5"> Smart pointers</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="unique_ptr.html" title="cpp/memory/unique ptr"><span class="t-lines"><span>unique_ptr</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><strong class="selflink"><span class="t-lines"><span>shared_ptr</span></span></strong></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="weak_ptr.html" title="cpp/memory/weak ptr"><span class="t-lines"><span>weak_ptr</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="auto_ptr.html" title="cpp/memory/auto ptr"><span class="t-lines"><span>auto_ptr</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-until-cxx17">(until C++17)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="owner_less.html" title="cpp/memory/owner less"><span class="t-lines"><span>owner_less</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="enable_shared_from_this.html" title="cpp/memory/enable shared from this"><span class="t-lines"><span>enable_shared_from_this</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="bad_weak_ptr.html" title="cpp/memory/bad weak ptr"><span class="t-lines"><span>bad_weak_ptr</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="default_delete.html" title="cpp/memory/default delete"><span class="t-lines"><span>default_delete</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv-h1"><td colspan="5"> Allocators</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="allocator.html" title="cpp/memory/allocator"><span class="t-lines"><span>allocator</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="allocator_traits.html" title="cpp/memory/allocator traits"><span class="t-lines"><span>allocator_traits</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="allocator_arg_t.html" title="cpp/memory/allocator arg t"><span class="t-lines"><span>allocator_arg_t</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="allocator_arg.html" title="cpp/memory/allocator arg"><span class="t-lines"><span>allocator_arg</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="uses_allocator.html" title="cpp/memory/uses allocator"><span class="t-lines"><span>uses_allocator</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="scoped_allocator_adaptor.html" title="cpp/memory/scoped allocator adaptor"><span class="t-lines"><span>scoped_allocator_adaptor</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv-h1"><td colspan="5"> Uninitialized storage</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="uninitialized_copy.html" title="cpp/memory/uninitialized copy"><span class="t-lines"><span>uninitialized_copy</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="uninitialized_copy_n.html" title="cpp/memory/uninitialized copy n"><span class="t-lines"><span>uninitialized_copy_n</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="uninitialized_fill.html" title="cpp/memory/uninitialized fill"><span class="t-lines"><span>uninitialized_fill</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="uninitialized_fill_n.html" title="cpp/memory/uninitialized fill n"><span class="t-lines"><span>uninitialized_fill_n</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="raw_storage_iterator.html" title="cpp/memory/raw storage iterator"><span class="t-lines"><span>raw_storage_iterator</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="get_temporary_buffer.html" title="cpp/memory/get temporary buffer"><span class="t-lines"><span>get_temporary_buffer</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="return_temporary_buffer.html" title="cpp/memory/return temporary buffer"><span class="t-lines"><span>return_temporary_buffer</span></span></a></div></div></td></tr>
<tr class="t-nv-h1"><td colspan="5"> Garbage collection support</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="gc/declare_reachable.html" title="cpp/memory/gc/declare reachable"><span class="t-lines"><span>declare_reachable</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="gc/undeclare_reachable.html" title="cpp/memory/gc/undeclare reachable"><span class="t-lines"><span>undeclare_reachable</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="gc/declare_no_pointers.html" title="cpp/memory/gc/declare no pointers"><span class="t-lines"><span>declare_no_pointers</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="gc/undeclare_no_pointers.html" title="cpp/memory/gc/undeclare no pointers"><span class="t-lines"><span>undeclare_no_pointers</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="gc/pointer_safety.html" title="cpp/memory/gc/pointer safety"><span class="t-lines"><span>pointer_safety</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="gc/get_pointer_safety.html" title="cpp/memory/gc/get pointer safety"><span class="t-lines"><span>get_pointer_safety</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv-h1"><td colspan="5"> Miscellaneous</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="pointer_traits.html" title="cpp/memory/pointer traits"><span class="t-lines"><span>pointer_traits</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="addressof.html" title="cpp/memory/addressof"><span class="t-lines"><span>addressof</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="align.html" title="cpp/memory/align"><span class="t-lines"><span>align</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div></td></tr>
<tr class="t-nv-h1"><td colspan="5"> <a href="c.html" title="cpp/memory/c">C Library</a></td></tr>
<tr class="t-nv-col-table"><td><div><table class="t-nv-begin" cellpadding="0" style="">
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="c/malloc.html" title="cpp/memory/c/malloc"><span class="t-lines"><span>malloc</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="c/calloc.html" title="cpp/memory/c/calloc"><span class="t-lines"><span>calloc</span></span></a></div></div></td></tr>
</table></div></td><td><div><table class="t-nv-begin" cellpadding="0" style="">
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="c/realloc.html" title="cpp/memory/c/realloc"><span class="t-lines"><span>realloc</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="c/free.html" title="cpp/memory/c/free"><span class="t-lines"><span>free</span></span></a></div></div></td></tr>
</table></div></td></tr>
<tr class="t-nv-h1"><td colspan="5"> <a href="new.1.html" title="cpp/memory/new">Low level memory management</a></td></tr>
</table></div><div><span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/memory/navbar_content&action=edit">[edit]</a></span></div></div></div></div><div class="t-navbar-sep"> </div><div class="t-navbar-head"><strong class="selflink"><tt>std::shared_ptr</tt></strong><div class="t-navbar-menu"><div><div><table class="t-nv-begin" cellpadding="0" style="">
<tr class="t-nv-h1"><td colspan="5"> Member functions</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="shared_ptr/shared_ptr.html" title="cpp/memory/shared ptr/shared ptr"><span class="t-lines"><span>shared_ptr::shared_ptr</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="shared_ptr/~shared_ptr.html" title="cpp/memory/shared ptr/~shared ptr"><span class="t-lines"><span>shared_ptr::~shared_ptr</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="shared_ptr/operator=.html" title="cpp/memory/shared ptr/operator="><span class="t-lines"><span>shared_ptr::operator=</span></span></a></div></div></td></tr>
<tr class="t-nv-h2"><td colspan="5"> Modifiers</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="shared_ptr/reset.html" title="cpp/memory/shared ptr/reset"><span class="t-lines"><span>shared_ptr::reset</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="shared_ptr/swap.html" title="cpp/memory/shared ptr/swap"><span class="t-lines"><span>shared_ptr::swap</span></span></a></div></div></td></tr>
<tr class="t-nv-h2"><td colspan="5"> Observers</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="shared_ptr/get.html" title="cpp/memory/shared ptr/get"><span class="t-lines"><span>shared_ptr::get</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="shared_ptr/operator*.html" title="cpp/memory/shared ptr/operator*"><span class="t-lines"><span>shared_ptr::operator*</span><span>shared_ptr::operator-></span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="shared_ptr/use_count.html" title="cpp/memory/shared ptr/use count"><span class="t-lines"><span>shared_ptr::use_count</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="shared_ptr/unique.html" title="cpp/memory/shared ptr/unique"><span class="t-lines"><span>shared_ptr::unique</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="shared_ptr/operator_bool.html" title="cpp/memory/shared ptr/operator bool"><span class="t-lines"><span>shared_ptr::operator bool</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="shared_ptr/owner_before.html" title="cpp/memory/shared ptr/owner before"><span class="t-lines"><span>shared_ptr::owner_before</span></span></a></div></div></td></tr>
<tr class="t-nv-h1"><td colspan="5"> Non-member functions</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="shared_ptr/swap2.html" title="cpp/memory/shared ptr/swap2"><span class="t-lines"><span>std::swap</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="shared_ptr/make_shared.html" title="cpp/memory/shared ptr/make shared"><span class="t-lines"><span>make_shared</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="shared_ptr/allocate_shared.html" title="cpp/memory/shared ptr/allocate shared"><span class="t-lines"><span>allocate_shared</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="shared_ptr/pointer_cast.html" title="cpp/memory/shared ptr/pointer cast"><span class="t-lines"><span>static_pointer_cast</span><span>dynamic_pointer_cast</span><span>const_pointer_cast</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="shared_ptr/get_deleter.html" title="cpp/memory/shared ptr/get deleter"><span class="t-lines"><span>get_deleter</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="shared_ptr/operator_cmp.html" title="cpp/memory/shared ptr/operator cmp"><span class="t-lines"><span>operator==</span><span>operator|=</span><span>operator<</span><span>operator<=</span><span>operator></span><span>operator>=</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="shared_ptr/operator_ltlt.html" title="cpp/memory/shared ptr/operator ltlt"><span class="t-lines"><span>operator<<</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="shared_ptr/atomic.html" title="cpp/memory/shared ptr/atomic"><span class="t-lines"><span>atomic_is_lock_free</span><span>atomic_load</span><span>atomic_load_explicit</span><span>atomic_store</span><span>atomic_store_explicit</span><span>atomic_exchange</span><span>atomic_exchange_explicit</span><span>atomic_compare_exchange_weak</span><span>atomic_compare_exchange_strong</span><span>atomic_compare_exchange_weak_explicit</span><span>atomic_compare_exchange_strong_explicit</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="shared_ptr/hash.html" title="cpp/memory/shared ptr/hash"><span class="t-lines"><span>std::hash</span></span></a></div></div></td></tr>
</table></div><div><span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/memory/shared_ptr/navbar_content&action=edit">[edit]</a></span></div></div></div></div><div class="t-navbar-sep"> </div></div>
<table class="t-dcl-begin"><tbody>
<tr class="t-dsc-header">
<td> <div>Defined in header <code><a href="../header/memory.html" title="cpp/header/memory"><memory></a></code>
</div></td>
<td></td>
<td></td>
</tr>
<tr class="t-dcl t-since-cxx11">
<td> <div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> T <span class="sy1">></span> <span class="kw1">class</span> shared_ptr<span class="sy4">;</span></span></div></td>
<td class="t-dcl-nopad"> </td>
<td> <span class="t-mark-rev t-since-cxx11">(since C++11)</span> </td>
</tr>
<tr class="t-dcl-sep"><td></td><td></td><td></td></tr>
</tbody></table>
<p><code>std::shared_ptr</code> is a smart pointer that retains shared ownership of an object through a pointer. Several <code>shared_ptr</code> objects may own the same object. The object is destroyed and its memory deallocated when either of the following happens:
</p>
<ul><li> the last remaining <code>shared_ptr</code> owning the object is destroyed.
</li></ul>
<ul><li> the last remaining <code>shared_ptr</code> owning the object is assigned another pointer via <span class="t-lc">operator=</span> or <span class="t-lc">reset()</span>.
</li></ul>
<p>The object is destroyed using <a href="../language/delete.html" title="cpp/language/delete"><tt>delete-expression</tt></a> or a custom deleter that is supplied to <code>shared_ptr</code> during construction.
</p><p>A <code>shared_ptr</code> can share ownership of an object while storing a pointer to another object. This feature can be used to point to member objects while owning the object they belong to. The stored pointer is the one accessed by <span class="t-c"><span class="mw-geshi cpp source-cpp">get<span class="br0">(</span><span class="br0">)</span></span></span>, the dereference and the comparison operators. The managed pointer is the one passed to the deleter when use count reaches zero.
</p><p>A <code>shared_ptr</code> may also own no objects, in which case it is called <i>empty</i> (an empty shared_ptr may have a non-null stored pointer if the aliasing constructor was used to create it)
</p><p>All specializations of <code>shared_ptr</code> meet the requirements of <a href="../concept/CopyConstructible.html" title="cpp/concept/CopyConstructible"><code>CopyConstructible</code></a>, <a href="../concept/CopyAssignable.html" title="cpp/concept/CopyAssignable"><code>CopyAssignable</code></a>, and <a href="../concept/LessThanComparable.html" title="cpp/concept/LessThanComparable"><code>LessThanComparable</code></a> and are <a href="../language/implicit_cast.html" title="cpp/language/implicit cast">contextually convertible</a> to <code>bool</code>.
</p><p>All member functions (including copy constructor and copy assignment) can be called by multiple threads on different instances of <code>shared_ptr</code> without additional synchronization even if these instances are copies and share ownership of the same object. If multiple threads of execution access the same <code>shared_ptr</code> without synchronization and any of those accesses uses a non-const member function of <code>shared_ptr</code> then a data race will occur; the <a href="shared_ptr/atomic.html" title="cpp/memory/shared ptr/atomic">shared_ptr overloads of atomic functions</a> can be used to prevent the data race.
</p>
<table id="toc" class="toc"><tr><td><div id="toctitle"><h2>Contents</h2></div>
<ul>
<li class="toclevel-1 tocsection-1"><a href="shared_ptr.html#Member_types"><span class="tocnumber">1</span> <span class="toctext">Member types</span></a></li>
<li class="toclevel-1 tocsection-2"><a href="shared_ptr.html#Member_functions"><span class="tocnumber">2</span> <span class="toctext">Member functions</span></a>
<ul>
<li class="toclevel-2"><a href="shared_ptr.html#Modifiers"><span class="tocnumber">2.1</span> <span class="toctext">Modifiers</span></a></li>
<li class="toclevel-2"><a href="shared_ptr.html#Observers"><span class="tocnumber">2.2</span> <span class="toctext">Observers</span></a></li>
</ul>
</li>
<li class="toclevel-1 tocsection-3"><a href="shared_ptr.html#Non-member_functions"><span class="tocnumber">3</span> <span class="toctext">Non-member functions</span></a></li>
<li class="toclevel-1 tocsection-4"><a href="shared_ptr.html#Helper_classes"><span class="tocnumber">4</span> <span class="toctext">Helper classes</span></a></li>
<li class="toclevel-1 tocsection-5"><a href="shared_ptr.html#Notes"><span class="tocnumber">5</span> <span class="toctext">Notes</span></a></li>
<li class="toclevel-1 tocsection-6"><a href="shared_ptr.html#Implementation_notes"><span class="tocnumber">6</span> <span class="toctext">Implementation notes</span></a></li>
<li class="toclevel-1 tocsection-7"><a href="shared_ptr.html#Example"><span class="tocnumber">7</span> <span class="toctext">Example</span></a></li>
</ul>
</td></tr></table>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/memory/shared_ptr&action=edit&section=1" title="Edit section: Member types">edit</a>]</span> <span class="mw-headline" id="Member_types">Member types</span></h3>
<table class="t-dsc-begin">
<tr class="t-dsc-hitem">
<td> Member type
</td>
<td> Definition
</td></tr>
<tr class="t-dsc">
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp">element_type</span></span>
</td>
<td> <span class="t-c"><span class="mw-geshi cpp source-cpp">T</span></span>
</td></tr>
</table>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/memory/shared_ptr&action=edit&section=2" title="Edit section: Member functions">edit</a>]</span> <span class="mw-headline" id="Member_functions">Member functions</span></h3>
<table class="t-dsc-begin">
<tr class="t-dsc">
<td> <div class="t-dsc-member-div t-dsc-member-nobold-div"><div><a href="shared_ptr/shared_ptr.html" title="cpp/memory/shared ptr/shared ptr"> <span class="t-lines"><span>(constructor)</span></span></a></div></div>
</td>
<td> constructs new <code>shared_ptr</code> <br /> <span class="t-mark">(public member function)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/memory/shared_ptr/dsc_constructor&action=edit">[edit]</a></span>
</td></tr>
<tr class="t-dsc">
<td> <div class="t-dsc-member-div t-dsc-member-nobold-div"><div><a href="shared_ptr/~shared_ptr.html" title="cpp/memory/shared ptr/~shared ptr"> <span class="t-lines"><span>(destructor)</span></span></a></div></div>
</td>
<td> destructs the owned object if no more <code>shared_ptr</code>s link to it <br /> <span class="t-mark">(public member function)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/memory/shared_ptr/dsc_destructor&action=edit">[edit]</a></span>
</td></tr>
<tr class="t-dsc">
<td> <div class="t-dsc-member-div"><div><a href="shared_ptr/operator=.html" title="cpp/memory/shared ptr/operator="> <span class="t-lines"><span>operator=</span></span></a></div></div>
</td>
<td> assigns the <code>shared_ptr</code> <br /> <span class="t-mark">(public member function)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/memory/shared_ptr/dsc_operator%3D&action=edit">[edit]</a></span>
</td></tr>
<tr>
<td colspan="2"> <h5> <span class="mw-headline" id="Modifiers"> Modifiers </span></h5>
</td></tr>
<tr class="t-dsc">
<td> <div class="t-dsc-member-div"><div><a href="shared_ptr/reset.html" title="cpp/memory/shared ptr/reset"> <span class="t-lines"><span>reset</span></span></a></div></div>
</td>
<td> replaces the managed object <br /> <span class="t-mark">(public member function)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/memory/shared_ptr/dsc_reset&action=edit">[edit]</a></span>
</td></tr>
<tr class="t-dsc">
<td> <div class="t-dsc-member-div"><div><a href="shared_ptr/swap.html" title="cpp/memory/shared ptr/swap"> <span class="t-lines"><span>swap</span></span></a></div></div>
</td>
<td> swaps the managed objects <br /> <span class="t-mark">(public member function)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/memory/shared_ptr/dsc_swap&action=edit">[edit]</a></span>
</td></tr>
<tr>
<td colspan="2"> <h5> <span class="mw-headline" id="Observers"> Observers </span></h5>
</td></tr>
<tr class="t-dsc">
<td> <div class="t-dsc-member-div"><div><a href="shared_ptr/get.html" title="cpp/memory/shared ptr/get"> <span class="t-lines"><span>get</span></span></a></div></div>
</td>
<td> returns a pointer to the managed object <br /> <span class="t-mark">(public member function)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/memory/shared_ptr/dsc_get&action=edit">[edit]</a></span>
</td></tr>
<tr class="t-dsc">
<td> <div class="t-dsc-member-div"><div><a href="shared_ptr/operator*.html" title="cpp/memory/shared ptr/operator*"> <span class="t-lines"><span>operator*</span><span>operator-></span></span></a></div></div>
</td>
<td> dereferences pointer to the managed object <br /> <span class="t-mark">(public member function)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/memory/shared_ptr/dsc_operator*&action=edit">[edit]</a></span>
</td></tr>
<tr class="t-dsc">
<td> <div class="t-dsc-member-div"><div><a href="shared_ptr/use_count.html" title="cpp/memory/shared ptr/use count"> <span class="t-lines"><span>use_count</span></span></a></div></div>
</td>
<td> returns the number of <code>shared_ptr</code> objects referring to the same managed object <br /> <span class="t-mark">(public member function)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/memory/shared_ptr/dsc_use_count&action=edit">[edit]</a></span>
</td></tr>
<tr class="t-dsc">
<td> <div class="t-dsc-member-div"><div><a href="shared_ptr/unique.html" title="cpp/memory/shared ptr/unique"> <span class="t-lines"><span>unique</span></span></a></div></div>
</td>
<td> checks whether the managed object is managed only by the current <code>shared_ptr</code> instance <br /> <span class="t-mark">(public member function)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/memory/shared_ptr/dsc_unique&action=edit">[edit]</a></span>
</td></tr>
<tr class="t-dsc">
<td> <div class="t-dsc-member-div"><div><a href="shared_ptr/operator_bool.html" title="cpp/memory/shared ptr/operator bool"> <span class="t-lines"><span>operator bool</span></span></a></div></div>
</td>
<td> checks if there is associated managed object <br /> <span class="t-mark">(public member function)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/memory/shared_ptr/dsc_operator_bool&action=edit">[edit]</a></span>
</td></tr>
<tr class="t-dsc">
<td> <div class="t-dsc-member-div"><div><a href="shared_ptr/owner_before.html" title="cpp/memory/shared ptr/owner before"> <span class="t-lines"><span>owner_before</span></span></a></div></div>
</td>
<td> provides owner-based ordering of shared pointers <br /> <span class="t-mark">(public member function)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/memory/shared_ptr/dsc_owner_before&action=edit">[edit]</a></span>
</td></tr>
</table>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/memory/shared_ptr&action=edit&section=3" title="Edit section: Non-member functions">edit</a>]</span> <span class="mw-headline" id="Non-member_functions">Non-member functions</span></h3>
<table class="t-dsc-begin">
<tr class="t-dsc">
<td> <div class="t-dsc-member-div"><div><a href="shared_ptr/make_shared.html" title="cpp/memory/shared ptr/make shared"> <span class="t-lines"><span>make_shared</span></span></a></div></div>
</td>
<td> creates a shared pointer that manages a new object <br /> <span class="t-mark">(function template)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/memory/shared_ptr/dsc_make_shared&action=edit">[edit]</a></span>
</td></tr>
<tr class="t-dsc">
<td> <div class="t-dsc-member-div"><div><a href="shared_ptr/allocate_shared.html" title="cpp/memory/shared ptr/allocate shared"> <span class="t-lines"><span>allocate_shared</span></span></a></div></div>
</td>
<td> creates a shared pointer that manages a new object allocated using an allocator <br /> <span class="t-mark">(function template)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/memory/shared_ptr/dsc_allocate_shared&action=edit">[edit]</a></span>
</td></tr>
<tr class="t-dsc">
<td> <div class="t-dsc-member-div"><div><a href="shared_ptr/pointer_cast.html" title="cpp/memory/shared ptr/pointer cast"> <span class="t-lines"><span>static_pointer_cast</span><span>dynamic_pointer_cast</span><span>const_pointer_cast</span></span></a></div></div>
</td>
<td> applies <a href="../language/static_cast.html" title="cpp/language/static cast"><tt>static_cast</tt></a>, <a href="../language/dynamic_cast.html" title="cpp/language/dynamic cast"><tt>dynamic_cast</tt></a> or <a href="../language/const_cast.html" title="cpp/language/const cast"><tt>const_cast</tt></a> to the type of the managed object <br /> <span class="t-mark">(function template)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/memory/shared_ptr/dsc_pointer_cast&action=edit">[edit]</a></span>
</td></tr>
<tr class="t-dsc">
<td> <div class="t-dsc-member-div"><div><a href="shared_ptr/get_deleter.html" title="cpp/memory/shared ptr/get deleter"> <span class="t-lines"><span>get_deleter</span></span></a></div></div>
</td>
<td> returns the deleter of specified type, if owned <br /> <span class="t-mark">(function template)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/memory/shared_ptr/dsc_get_deleter&action=edit">[edit]</a></span>
</td></tr>
<tr class="t-dsc">
<td> <div class="t-dsc-member-div"><div><a href="shared_ptr/operator_cmp.html" title="cpp/memory/shared ptr/operator cmp"> <span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator<</span><span>operator<=</span><span>operator></span><span>operator>=</span></span></a></div></div>
</td>
<td> compares with another <code>shared_ptr</code> or with <span class="t-c"><span class="mw-geshi cpp source-cpp">nullptr</span></span> <br /> <span class="t-mark">(function template)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/memory/shared_ptr/dsc_operator_cmp&action=edit">[edit]</a></span>
</td></tr>
<tr class="t-dsc">
<td> <div class="t-dsc-member-div"><div><a href="shared_ptr/operator_ltlt.html" title="cpp/memory/shared ptr/operator ltlt"> <span class="t-lines"><span>operator<<</span></span></a></div></div>
</td>
<td> outputs the value of the managed pointer to an output stream <br /> <span class="t-mark">(function template)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/memory/shared_ptr/dsc_operator_ltlt&action=edit">[edit]</a></span>
</td></tr>
<tr class="t-dsc">
<td> <div class="t-dsc-member-div"><div><a href="shared_ptr/swap2.html" title="cpp/memory/shared ptr/swap2"> <span class="t-lines"><span>std::swap<span class="t-dsc-small">(std::shared_ptr)</span></span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div>
</td>
<td> specializes the <span class="t-lc">std::swap</span> algorithm <br /> <span class="t-mark">(function template)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/memory/shared_ptr/dsc_swap2&action=edit">[edit]</a></span>
</td></tr>
</table>
<table class="t-dsc-begin">
<tr class="t-dsc">
<td> <div class="t-dsc-member-div"><div><a href="shared_ptr/atomic.html" title="cpp/memory/shared ptr/atomic"> <span class="t-lines"><span>std::atomic_is_lock_free<span class="t-dsc-small">(std::shared_ptr)</span></span><span>std::atomic_load<span class="t-dsc-small">(std::shared_ptr)</span></span><span>std::atomic_load_explicit<span class="t-dsc-small">(std::shared_ptr)</span></span><span>std::atomic_store<span class="t-dsc-small">(std::shared_ptr)</span></span><span>std::atomic_store_explicit<span class="t-dsc-small">(std::shared_ptr)</span></span><span>std::atomic_exchange<span class="t-dsc-small">(std::shared_ptr)</span></span><span>std::atomic_exchange_explicit<span class="t-dsc-small">(std::shared_ptr)</span></span><span>std::atomic_compare_exchange_weak<span class="t-dsc-small">(std::shared_ptr)</span></span><span>std::atomic_compare_exchange_strong<span class="t-dsc-small">(std::shared_ptr)</span></span><span>std::atomic_compare_exchange_weak_explicit<span class="t-dsc-small">(std::shared_ptr)</span></span><span>std::atomic_compare_exchange_strong_explicit<span class="t-dsc-small">(std::shared_ptr)</span></span></span></a></div></div>
</td>
<td> specializes atomic operations <br /> <span class="t-mark">(function template)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/memory/shared_ptr/dsc_atomic&action=edit">[edit]</a></span>
</td></tr>
</table>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/memory/shared_ptr&action=edit&section=4" title="Edit section: Helper classes">edit</a>]</span> <span class="mw-headline" id="Helper_classes">Helper classes</span></h3>
<table class="t-dsc-begin">
<tr class="t-dsc">
<td> <div class="t-dsc-member-div"><div><a href="shared_ptr/hash.html" title="cpp/memory/shared ptr/hash"> <span class="t-lines"><span>std::hash<span class="t-dsc-small"><std::shared_ptr></span></span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div></div>
</td>
<td> hash support for <span class="t-lc">std::shared_ptr</span> <br /> <span class="t-mark">(class template specialization)</span> <span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:cpp/memory/shared_ptr/dsc_hash&action=edit">[edit]</a></span>
</td></tr>
</table>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/memory/shared_ptr&action=edit&section=5" title="Edit section: Notes">edit</a>]</span> <span class="mw-headline" id="Notes">Notes</span></h3>
<p>The ownership of an object can only be shared with another <code>shared_ptr</code> by copy constructing or copy assigning its value to another <code>shared_ptr</code>. Constructing a new <code>shared_ptr</code> using the raw underlying pointer owned by another <code>shared_ptr</code> leads to undefined behavior.
</p><p><code>std::shared_ptr</code> may be used with an <a href="../language/incomplete_type.html" title="cpp/language/incomplete type" class="mw-redirect">incomplete type</a> <code>T</code>, but <code>T</code> must be complete at the point in code where the constructor from a raw pointer or the <code>reset(T*)</code> member function is called (note that <span class="t-lc">std::unique_ptr</span> may be constructed from a raw pointer to an incomplete type).
</p>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/memory/shared_ptr&action=edit&section=6" title="Edit section: Implementation notes">edit</a>]</span> <span class="mw-headline" id="Implementation_notes">Implementation notes</span></h3>
<p>In a typical implementation, <span class="t-lc">std::shared_ptr</span> holds only two pointers:
</p>
<ul><li> the stored pointer (one returned by <span class="t-c"><span class="mw-geshi cpp source-cpp">get<span class="br0">(</span><span class="br0">)</span></span></span>)
</li><li> a pointer to <i>control block</i>
</li></ul>
<p>The control block is a dynamically-allocated object that holds:
</p>
<ul><li> either a pointer to the managed object or the managed object itself
</li><li> the deleter (type-erased)
</li><li> the allocator (type-erased)
</li><li> the number of <code>shared_ptr</code>s that own the managed object
</li><li> the number of <code>weak_ptr</code>s that refer to the managed object
</li></ul>
<p>When <code>shared_ptr</code> is created by calling <span class="t-lc">std::make_shared</span> or <span class="t-lc">std::allocate_shared</span>, the memory for both the control block and the managed object is created with a single allocation. The managed object is constructed in-place in a data member of the control block. When <code>shared_ptr</code> is created via one of the <code>shared_ptr</code> constructors, the managed object and the control block must be allocated separately. In this case, the control block stores a pointer to the managed object.
</p><p>The pointer held by the <code>shared_ptr</code> directly is the one returned by <span class="t-lc">get()</span>, while the pointer/object held by the control block is the one that will be deleted when the number of shared owners reaches zero. These pointers are not necessarily equal.
</p><p>The destructor of <code>shared_ptr</code> decrements the number of shared owners of the control block. If that counter reaches zero, the control block calls the destructor of the managed object. The control block does not deallocate itself until the <span class="t-lc">std::weak_ptr</span> counter reaches zero as well.
</p><p>In practical implementations, the number of weak pointers <a rel="nofollow" class="external text" href="https://www.reddit.com/r/cpp/comments/3eia29/stdshared_ptrs_secret_constructor/ctfeh1p">may be incremented</a> if there is a shared pointer to the same control block.
</p><p>To satisfy thread safety requirements, the reference counters are typically incremented and decremented using an equivalent of <span class="t-lc">std::atomic::fetch_add</span> with <span class="t-lc">std::memory_order_relaxed</span>.
</p>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=cpp/memory/shared_ptr&action=edit&section=7" title="Edit section: Example">edit</a>]</span> <span class="mw-headline" id="Example">Example</span></h3>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">Run this code</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="co2">#include <iostream></span>
<span class="co2">#include <memory></span>
<span class="co2">#include <thread></span>
<span class="co2">#include <chrono></span>
<span class="co2">#include <mutex></span>
 
<span class="kw1">struct</span> Base
<span class="br0">{</span>
Base<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> <a href="../io/cout.html"><span class="kw1480">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">" Base::Base()<span class="es1">\n</span>"</span><span class="sy4">;</span> <span class="br0">}</span>
<span class="co1">// Note: non-virtual destructor is OK here</span>
~Base<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> <a href="../io/cout.html"><span class="kw1480">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">" Base::~Base()<span class="es1">\n</span>"</span><span class="sy4">;</span> <span class="br0">}</span>
<span class="br0">}</span><span class="sy4">;</span>
<span class="kw1">struct</span> Derived<span class="sy4">:</span> <span class="kw1">public</span> Base
<span class="br0">{</span>
Derived<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> <a href="../io/cout.html"><span class="kw1480">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">" Derived::Derived()<span class="es1">\n</span>"</span><span class="sy4">;</span> <span class="br0">}</span>
~Derived<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> <a href="../io/cout.html"><span class="kw1480">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">" Derived::~Derived()<span class="es1">\n</span>"</span><span class="sy4">;</span> <span class="br0">}</span>
<span class="br0">}</span><span class="sy4">;</span>
 
<span class="kw4">void</span> thr<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">shared_ptr</span><span class="sy1"><</span>Base<span class="sy1">></span> p<span class="br0">)</span>
<span class="br0">{</span>
<a href="../thread/sleep_for.html"><span class="kw1828">std::<span class="me2">this_thread</span><span class="sy4">::</span><span class="me2">sleep_for</span></span></a><span class="br0">(</span><a href="../chrono/duration.html"><span class="kw874">std::<span class="me2">chrono</span><span class="sy4">::</span><span class="me2">seconds</span></span></a><span class="br0">(</span><span class="nu0">1</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
std<span class="sy4">::</span><span class="me2">shared_ptr</span><span class="sy1"><</span>Base<span class="sy1">></span> lp <span class="sy1">=</span> p<span class="sy4">;</span> <span class="co1">// thread-safe, even though the</span>
<span class="co1">// shared use_count is incremented</span>
<span class="br0">{</span>
<span class="kw4">static</span> <a href="../thread/mutex.html"><span class="kw1831">std::<span class="me2">mutex</span></span></a> io_mutex<span class="sy4">;</span>
<a href="../thread/lock_guard.html"><span class="kw1843">std::<span class="me2">lock_guard</span></span></a><span class="sy1"><</span><a href="../thread/mutex.html"><span class="kw1831">std::<span class="me2">mutex</span></span></a><span class="sy1">></span> lk<span class="br0">(</span>io_mutex<span class="br0">)</span><span class="sy4">;</span>
<a href="../io/cout.html"><span class="kw1480">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"local pointer in a thread:<span class="es1">\n</span>"</span>
<span class="sy1"><<</span> <span class="st0">" lp.get() = "</span> <span class="sy1"><<</span> lp.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span>
<span class="sy1"><<</span> <span class="st0">", lp.use_count() = "</span> <span class="sy1"><<</span> lp.<span class="me1">use_count</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
<span class="br0">}</span>
<span class="br0">}</span>
 
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
std<span class="sy4">::</span><span class="me2">shared_ptr</span><span class="sy1"><</span>Base<span class="sy1">></span> p <span class="sy1">=</span> <a href="shared_ptr/make_shared.html"><span class="kw616">std::<span class="me2">make_shared</span></span></a><span class="sy1"><</span>Derived<span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
 
<a href="../io/cout.html"><span class="kw1480">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Created a shared Derived (as a pointer to Base)<span class="es1">\n</span>"</span>
<span class="sy1"><<</span> <span class="st0">" p.get() = "</span> <span class="sy1"><<</span> p.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span>
<span class="sy1"><<</span> <span class="st0">", p.use_count() = "</span> <span class="sy1"><<</span> p.<span class="me1">use_count</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
<a href="../thread/thread.html"><span class="kw1825">std::<span class="me2">thread</span></span></a> t1<span class="br0">(</span>thr, p<span class="br0">)</span>, t2<span class="br0">(</span>thr, p<span class="br0">)</span>, t3<span class="br0">(</span>thr, p<span class="br0">)</span><span class="sy4">;</span>
p.<span class="me1">reset</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// release ownership from main</span>
<a href="../io/cout.html"><span class="kw1480">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Shared ownership between 3 threads and released<span class="es1">\n</span>"</span>
<span class="sy1"><<</span> <span class="st0">"ownership from main:<span class="es1">\n</span>"</span>
<span class="sy1"><<</span> <span class="st0">" p.get() = "</span> <span class="sy1"><<</span> p.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span>
<span class="sy1"><<</span> <span class="st0">", p.use_count() = "</span> <span class="sy1"><<</span> p.<span class="me1">use_count</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
t1.<span class="me1">join</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> t2.<span class="me1">join</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> t3.<span class="me1">join</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
<a href="../io/cout.html"><span class="kw1480">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"All threads completed, the last one deleted Derived<span class="es1">\n</span>"</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div></div>
<p>Possible output:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="text source-text"><pre class="de1">Base::Base()
Derived::Derived()
Created a shared Derived (as a pointer to Base)
p.get() = 0xc99028, p.use_count() = 1
Shared ownership between 3 threads and released
ownership from main:
p.get() = (nil), p.use_count() = 0
local pointer in a thread:
lp.get() = 0xc99028, lp.use_count() = 3
local pointer in a thread:
lp.get() = 0xc99028, lp.use_count() = 4
local pointer in a thread:
lp.get() = 0xc99028, lp.use_count() = 2
Derived::~Derived()
Base::~Base()
All threads completed, the last one deleted Derived</pre></div></div>
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