std::unique_ptr

谁借莪１个温暖的怀抱￠ 2022-06-10 10:17 102阅读 0赞

# std::unique\_ptr #

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      定义于头文件&nbsp; 
     <code style="font-family:DejaVuSansMono,&quot;DejaVu Sans Mono&quot;,courier,monospace!important; background-color:transparent"><a href="http://zh.cppreference.com/mwiki/index.php?title=cpp/header/memory&amp;action=edit&amp;redlink=1" title="cpp/header/memory（页面不存在）" style="text-decoration:none; color:rgb(165,88,88); background:none" rel="nofollow">&lt;memory&gt;</a></code> 
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   <td style="border-top:1px solid rgb(204,204,204); padding:0.3em 2em 0.2em 1em; font-size:1em"> <span style="font-family:monospace; line-height:1.1em; white-space:nowrap; margin:0px; padding:0px"><span style="line-height:1.1em; margin:0px; padding:0px; color:rgb(0,0,221)">template</span><span style="line-height:1.1em; margin:0px; padding:0px; color:rgb(0,0,128)">&lt;</span><br> </span> <p style="margin-top:0px; margin-bottom:0px; line-height:1.1em; padding-top:0px; padding-bottom:0px"> &nbsp; &nbsp;&nbsp;<span style="line-height:1.1em; margin:0px; padding:0px; color:rgb(0,0,221)">class</span>&nbsp;T,<br> &nbsp; &nbsp;&nbsp;<span style="line-height:1.1em; margin:0px; padding:0px; color:rgb(0,0,221)">class</span>&nbsp;Deleter&nbsp;<span style="line-height:1.1em; margin:0px; padding:0px; color:rgb(0,0,128)">=</span>&nbsp;<a href="http://zh.cppreference.com/w/cpp/memory/default_delete" style="text-decoration:none; color:rgb(0,48,128); background:none" rel="nofollow"><span style="line-height:1.1em; margin:0px; padding:0px">std::<span style="line-height:1.1em; margin:0px; padding:0px">default_delete</span></span></a><span style="line-height:1.1em; margin:0px; padding:0px; color:rgb(0,0,128)">&lt;</span>T<span style="line-height:1.1em; margin:0px; padding:0px; color:rgb(0,0,128)">&gt;</span><br> </p> <span style="line-height:1.1em; margin:0px; padding:0px; color:rgb(0,0,128)">&gt;</span>&nbsp;<span style="line-height:1.1em; margin:0px; padding:0px; color:rgb(0,0,221)">class</span>&nbsp;unique_ptr<span style="line-height:1.1em; margin:0px; padding:0px; color:rgb(0,128,128)">;</span></td> 
   <td style="border-top:1px solid rgb(204,204,204); font-size:0.8em; padding-right:1.5em"> (1)</td> 
   <td style="border-top:1px solid rgb(204,204,204); padding:0px"><span style="color:rgb(0,128,0); font-size:0.8em">(C++11 起)</span></td> 
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   <td style="border-top:1px solid rgb(204,204,204); padding:0.3em 2em 0.2em 1em; font-size:1em"> <span style="font-family:monospace; line-height:1.1em; white-space:nowrap; margin:0px; padding:0px"><span style="line-height:1.1em; margin:0px; padding:0px; color:rgb(0,0,221)">template</span>&nbsp;<span style="line-height:1.1em; margin:0px; padding:0px; color:rgb(0,0,128)">&lt;</span><br> </span> <p style="margin-top:0px; margin-bottom:0px; line-height:1.1em; padding-top:0px; padding-bottom:0px"> &nbsp; &nbsp;&nbsp;<span style="line-height:1.1em; margin:0px; padding:0px; color:rgb(0,0,221)">class</span>&nbsp;T,<br> &nbsp; &nbsp;&nbsp;<span style="line-height:1.1em; margin:0px; padding:0px; color:rgb(0,0,221)">class</span>&nbsp;Deleter<br> </p> <span style="line-height:1.1em; margin:0px; padding:0px; color:rgb(0,0,128)">&gt;</span>&nbsp;<span style="line-height:1.1em; margin:0px; padding:0px; color:rgb(0,0,221)">class</span>&nbsp;unique_ptr<span style="line-height:1.1em; margin:0px; padding:0px; color:rgb(0,0,128)">&lt;</span>T<span style="line-height:1.1em; margin:0px; padding:0px; color:rgb(0,128,0)">[</span><span style="line-height:1.1em; margin:0px; padding:0px; color:rgb(0,128,0)">]</span>,Deleter<span style="line-height:1.1em; margin:0px; padding:0px; color:rgb(0,0,128)">&gt;</span><span style="line-height:1.1em; margin:0px; padding:0px; color:rgb(0,128,128)">;</span></td> 
   <td style="border-top:1px solid rgb(204,204,204); font-size:0.8em; padding-right:1.5em"> (2)</td> 
   <td style="border-top:1px solid rgb(204,204,204); padding:0px"><span style="color:rgb(0,128,0); font-size:0.8em">(C++11 起)</span></td> 
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`std::unique_ptr`是具有以下特性的智能指针：

*  通过指针保留了唯一的对象的所有权，并且
 *  `unique_ptr`离开作用域时，会析构指向的对象。

`unique_ptr`不能复制或者复制赋值，两个`unique_ptr`实例不能管理同一个对象。一个非const的`unique_ptr`可以将所管理对象的所有权转移到另一个`unique_ptr`。一个const std::unique\_ptr不能转让，而是将所管理对象的生命周期限制在指针所创建的作用域之中。当`unique_ptr`销毁时，会通过`Deleter`销毁所管理的对象

有两个版本的`std::unique_ptr`

1) 管理单一的对象的生命周期，例如使用 new 来分配

2) 管理一个数组的生命周期与运行时间长度，例如使用 new\[\] 分配

`std::unique_ptr`的典型用途包括

*  提供异常安全的类和函数来处理具有动态生命周期的对象，通过确保正常和异常情况下退出时的删除操作。

*  通过函数传递独有的动态生命周期对象的所有权

*  从函数获得独有的动态生命周期对象的所有权

*  作为移动感知的容器，类似于std::vector持有动态分配的对象的指针，例如如果需要多态行为

### 成员类型 ###

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   <td style="font-weight:bold; line-height:1.1em; padding:0.2em 0px 0.25em 0.75em; white-space:nowrap; border-top:1px solid rgb(204,204,204)"> 成员类型</td> 
   <td style="font-weight:bold; line-height:1.1em; padding:0.2em 0px 0.25em 0.75em; white-space:nowrap; border-top:1px solid rgb(204,204,204)"> 定义</td> 
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   <td style="border-top:1px solid rgb(204,204,204); width:102.406px; line-height:1.2em; padding:0.2em 0px 0.25em 0.75em; white-space:nowrap"> <span style="border:1px solid rgb(214,214,214); margin:0px 2px; padding:0px 2px; display:inline-block"><span style="font-family:monospace; line-height:normal">pointer</span></span></td> 
   <td style="border-top:1px solid rgb(204,204,204); line-height:1.1em; padding-left:0.75em"> <span style="border:1px solid rgb(214,214,214); margin:0px 2px; padding:0px 2px; display:inline-block"><span style="font-family:monospace; line-height:normal; white-space:nowrap"><a href="http://zh.cppreference.com/w/cpp/types/remove_reference" style="text-decoration:none; color:rgb(0,48,128); background:none" rel="nofollow"><span>std::<span>remove_reference</span></span></a><span style="color:rgb(0,0,128)">&lt;</span>D<span style="color:rgb(0,0,128)">&gt;</span><span style="color:rgb(0,128,128)">::</span><span>type</span><span style="color:rgb(0,128,128)">::</span><span>pointer</span></span></span>如果存在该类型的，否则T *</td> 
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   <td style="border-top:1px solid rgb(204,204,204); width:102.406px; line-height:1.2em; padding:0.2em 0px 0.25em 0.75em; white-space:nowrap"> <span style="border:1px solid rgb(214,214,214); margin:0px 2px; padding:0px 2px; display:inline-block"><span style="font-family:monospace; line-height:normal">element_type</span></span></td> 
   <td style="border-top:1px solid rgb(204,204,204); line-height:1.1em; padding-left:0.75em"> <code style="font-family:DejaVuSansMono,&quot;DejaVu Sans Mono&quot;,courier,monospace!important; background-color:transparent">T</code>，该对象的类型的此<code style="font-family:DejaVuSansMono,&quot;DejaVu Sans Mono&quot;,courier,monospace!important; background-color:transparent">unique_ptr</code>管理</td> 
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   <td style="border-top:1px solid rgb(204,204,204); width:102.406px; line-height:1.2em; padding:0.2em 0px 0.25em 0.75em; white-space:nowrap"> <span style="border:1px solid rgb(214,214,214); margin:0px 2px; padding:0px 2px; display:inline-block"><span style="font-family:monospace; line-height:normal">deleter_type</span></span></td> 
   <td style="border-top:1px solid rgb(204,204,204); line-height:1.1em; padding-left:0.75em"> <code style="font-family:DejaVuSansMono,&quot;DejaVu Sans Mono&quot;,courier,monospace!important; background-color:transparent">Deleter</code>，函数对象或左值引用函数或函数对象，被调用的析构函数</td> 
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### 成员函数 ###

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      <a href="http://zh.cppreference.com/w/cpp/memory/unique_ptr/unique_ptr" title="cpp/memory/unique ptr/unique ptr" style="text-decoration:none; color:rgb(11,0,128); background:none" rel="nofollow">(构造函数)</a> 
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   <td style="border-top:1px solid rgb(204,204,204); line-height:1.1em; padding-left:0.75em"> 构造新的<code style="font-family:DejaVuSansMono,&quot;DejaVu Sans Mono&quot;,courier,monospace!important; background-color:transparent">unique_ptr</code>&nbsp;<br> <span style="color:rgb(0,128,0); font-size:0.8em">(公开成员函数)</span><span title="编辑此模板" style="float:right; display:inline; margin-left:5px; font-size:0.7em"><a href="http://zh.cppreference.com/mwiki/index.php?title=Template:cpp/memory/unique_ptr/dsc_constructor&amp;action=edit" style="text-decoration:none; color:rgb(102,51,102); padding-top:0px!important; padding-right:13px; padding-bottom:0px!important; padding-left:0px!important" rel="nofollow">[编辑]</a></span></td> 
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      <a href="http://zh.cppreference.com/w/cpp/memory/unique_ptr/~unique_ptr" title="cpp/memory/unique ptr/~unique ptr" style="text-decoration:none; color:rgb(11,0,128); background:none" rel="nofollow">(析构函数)</a> 
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   <td style="border-top:1px solid rgb(204,204,204); line-height:1.1em; padding-left:0.75em"> 析构所管理的对象，如果存在的话&nbsp;<br> <span style="color:rgb(0,128,0); font-size:0.8em">(公开成员函数)</span><span title="编辑此模板" style="float:right; display:inline; margin-left:5px; font-size:0.7em"><a href="http://zh.cppreference.com/mwiki/index.php?title=Template:cpp/memory/unique_ptr/dsc_destructor&amp;action=edit" style="text-decoration:none; color:rgb(102,51,102); padding-top:0px!important; padding-right:13px; padding-bottom:0px!important; padding-left:0px!important" rel="nofollow">[编辑]</a></span></td> 
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      <a href="http://zh.cppreference.com/w/cpp/memory/unique_ptr/operator%3D" title="cpp/memory/unique ptr/operator=" style="text-decoration:none; color:rgb(11,0,128); background:none" rel="nofollow">operator=</a> 
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   <td style="border-top:1px solid rgb(204,204,204); line-height:1.1em; padding-left:0.75em"> 为<code style="font-family:DejaVuSansMono,&quot;DejaVu Sans Mono&quot;,courier,monospace!important; background-color:transparent">unique_ptr</code>赋值&nbsp;<br> <span style="color:rgb(0,128,0); font-size:0.8em">(公开成员函数)</span><span title="编辑此模板" style="float:right; display:inline; margin-left:5px; font-size:0.7em"><a href="http://zh.cppreference.com/mwiki/index.php?title=Template:cpp/memory/unique_ptr/dsc_operator%3D&amp;action=edit" style="text-decoration:none; color:rgb(102,51,102); padding-top:0px!important; padding-right:13px; padding-bottom:0px!important; padding-left:0px!important" rel="nofollow">[编辑]</a></span></td> 
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      <a href="http://zh.cppreference.com/w/cpp/memory/unique_ptr/release" title="cpp/memory/unique ptr/release" style="text-decoration:none; color:rgb(11,0,128); background:none" rel="nofollow">release</a> 
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   <td style="border-top:1px solid rgb(204,204,204); line-height:1.1em; padding-left:0.75em"> 返回一个指向被管理对象的指针，并释放所有权&nbsp;<br> <span style="color:rgb(0,128,0); font-size:0.8em">(公开成员函数)</span><span title="编辑此模板" style="float:right; display:inline; margin-left:5px; font-size:0.7em"><a href="http://zh.cppreference.com/mwiki/index.php?title=Template:cpp/memory/unique_ptr/dsc_release&amp;action=edit" style="text-decoration:none; color:rgb(102,51,102); padding-top:0px!important; padding-right:13px; padding-bottom:0px!important; padding-left:0px!important" rel="nofollow">[编辑]</a></span></td> 
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      <a href="http://zh.cppreference.com/w/cpp/memory/unique_ptr/reset" title="cpp/memory/unique ptr/reset" style="text-decoration:none; color:rgb(11,0,128); background:none" rel="nofollow">reset</a> 
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   <td style="border-top:1px solid rgb(204,204,204); line-height:1.1em; padding-left:0.75em"> 替换所管理的对象&nbsp;<br> <span style="color:rgb(0,128,0); font-size:0.8em">(公开成员函数)</span><span title="编辑此模板" style="float:right; display:inline; margin-left:5px; font-size:0.7em"><a href="http://zh.cppreference.com/mwiki/index.php?title=Template:cpp/memory/unique_ptr/dsc_reset&amp;action=edit" style="text-decoration:none; color:rgb(102,51,102); padding-top:0px!important; padding-right:13px; padding-bottom:0px!important; padding-left:0px!important" rel="nofollow">[编辑]</a></span></td> 
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     <div style="padding:0px; display:inline-table; vertical-align:middle; font-weight:bold; font-family:DejaVuSansMono,&quot;DejaVu Sans Mono&quot;,courier,monospace"> 
      <a href="http://zh.cppreference.com/w/cpp/memory/unique_ptr/swap" title="cpp/memory/unique ptr/swap" style="text-decoration:none; color:rgb(11,0,128); background:none" rel="nofollow">swap</a> 
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   <td style="border-top:1px solid rgb(204,204,204); line-height:1.1em; padding-left:0.75em"> 交换所管理的对象&nbsp;<br> <span style="color:rgb(0,128,0); font-size:0.8em">(公开成员函数)</span><span title="编辑此模板" style="float:right; display:inline; margin-left:5px; font-size:0.7em"><a href="http://zh.cppreference.com/mwiki/index.php?title=Template:cpp/memory/unique_ptr/dsc_swap&amp;action=edit" style="text-decoration:none; color:rgb(102,51,102); padding-top:0px!important; padding-right:13px; padding-bottom:0px!important; padding-left:0px!important" rel="nofollow">[编辑]</a></span></td> 
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     <div style="padding:0px; display:inline-table; vertical-align:middle; font-weight:bold; font-family:DejaVuSansMono,&quot;DejaVu Sans Mono&quot;,courier,monospace"> 
      <a href="http://zh.cppreference.com/w/cpp/memory/unique_ptr/get" title="cpp/memory/unique ptr/get" style="text-decoration:none; color:rgb(11,0,128); background:none" rel="nofollow">get</a> 
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   <td style="border-top:1px solid rgb(204,204,204); line-height:1.1em; padding-left:0.75em"> 返回指向被管理对象的指针&nbsp;<br> <span style="color:rgb(0,128,0); font-size:0.8em">(公开成员函数)</span><span title="编辑此模板" style="float:right; display:inline; margin-left:5px; font-size:0.7em"><a href="http://zh.cppreference.com/mwiki/index.php?title=Template:cpp/memory/unique_ptr/dsc_get&amp;action=edit" style="text-decoration:none; color:rgb(102,51,102); padding-top:0px!important; padding-right:13px; padding-bottom:0px!important; padding-left:0px!important" rel="nofollow">[编辑]</a></span></td> 
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      <a href="http://zh.cppreference.com/w/cpp/memory/unique_ptr/get_deleter" title="cpp/memory/unique ptr/get deleter" style="text-decoration:none; color:rgb(11,0,128); background:none" rel="nofollow">get_deleter</a> 
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   <td style="border-top:1px solid rgb(204,204,204); line-height:1.1em; padding-left:0.75em"> 返回删除器，用于被管理对象的析构&nbsp;<br> <span style="color:rgb(0,128,0); font-size:0.8em">(公开成员函数)</span><span title="编辑此模板" style="float:right; display:inline; margin-left:5px; font-size:0.7em"><a href="http://zh.cppreference.com/mwiki/index.php?title=Template:cpp/memory/unique_ptr/dsc_get_deleter&amp;action=edit" style="text-decoration:none; color:rgb(102,51,102); padding-top:0px!important; padding-right:13px; padding-bottom:0px!important; padding-left:0px!important" rel="nofollow">[编辑]</a></span></td> 
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      <a href="http://zh.cppreference.com/w/cpp/memory/unique_ptr/operator_bool" title="cpp/memory/unique ptr/operator bool" style="text-decoration:none; color:rgb(11,0,128); background:none" rel="nofollow">operator bool</a> 
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    </div> </td> 
   <td style="border-top:1px solid rgb(204,204,204); line-height:1.1em; padding-left:0.75em"> 检查是否有关联的被管理对象&nbsp;<br> <span style="color:rgb(0,128,0); font-size:0.8em">(公开成员函数)</span><span title="编辑此模板" style="float:right; display:inline; margin-left:5px; font-size:0.7em"><a href="http://zh.cppreference.com/mwiki/index.php?title=Template:cpp/memory/unique_ptr/dsc_operator_bool&amp;action=edit" style="text-decoration:none; color:rgb(102,51,102); padding-top:0px!important; padding-right:13px; padding-bottom:0px!important; padding-left:0px!important" rel="nofollow">[编辑]</a></span></td> 
  </tr> 
  <tr> 
   <td colspan="2"> <h5 style="background:none; margin:0px 0px 0.3em; overflow:hidden; padding-top:0.5em; padding-bottom:0.17em; border-bottom:none; width:auto; font-size:12.8px"> <span>单个对象版本，unique_ptr&lt;T&gt;</span></h5> </td> 
  </tr> 
  <tr> 
   <td style="border-top:1px solid rgb(204,204,204); width:100.406px; line-height:1.2em; padding:0.2em 0px 0.25em 0.75em; white-space:nowrap"> 
    <div> 
     <div style="padding:0px; display:inline-table; vertical-align:middle; font-weight:bold; font-family:DejaVuSansMono,&quot;DejaVu Sans Mono&quot;,courier,monospace"> 
      <a href="http://zh.cppreference.com/w/cpp/memory/unique_ptr/operator*" title="cpp/memory/unique ptr/operator*" style="text-decoration:none; color:rgb(11,0,128); background:none" rel="nofollow">operator*<br> operator-&gt;</a> 
     </div> 
    </div> </td> 
   <td style="border-top:1px solid rgb(204,204,204); line-height:1.1em; padding-left:0.75em"> 对指向被管理对象的指针进行解引用&nbsp;<br> <span style="color:rgb(0,128,0); font-size:0.8em">(公开成员函数)</span><span title="编辑此模板" style="float:right; display:inline; margin-left:5px; font-size:0.7em"><a href="http://zh.cppreference.com/mwiki/index.php?title=Template:cpp/memory/unique_ptr/dsc_operator*&amp;action=edit" style="text-decoration:none; color:rgb(102,51,102); padding-top:0px!important; padding-right:13px; padding-bottom:0px!important; padding-left:0px!important" rel="nofollow">[编辑]</a></span></td> 
  </tr> 
  <tr> 
   <td colspan="2"> <h5 style="background:none; margin:0px 0px 0.3em; overflow:hidden; padding-top:0.5em; padding-bottom:0.17em; border-bottom:none; width:auto; font-size:12.8px"> <span>数组版本，unique_ptr&lt;T[]&gt;</span></h5> </td> 
  </tr> 
  <tr> 
   <td style="border-top:1px solid rgb(204,204,204); width:100.406px; line-height:1.2em; padding:0.2em 0px 0.25em 0.75em; white-space:nowrap"> 
    <div> 
     <div style="padding:0px; display:inline-table; vertical-align:middle; font-weight:bold; font-family:DejaVuSansMono,&quot;DejaVu Sans Mono&quot;,courier,monospace"> 
      <a href="http://zh.cppreference.com/w/cpp/memory/unique_ptr/operator_at" title="cpp/memory/unique ptr/operator at" style="text-decoration:none; color:rgb(11,0,128); background:none" rel="nofollow">operator[]</a> 
     </div> 
    </div> </td> 
   <td style="border-top:1px solid rgb(204,204,204); line-height:1.1em; padding-left:0.75em"> 提供对所管理数组的按索引访问&nbsp;<br> <span style="color:rgb(0,128,0); font-size:0.8em">(公开成员函数)</span><span title="编辑此模板" style="float:right; display:inline; margin-left:5px; font-size:0.7em"><a href="http://zh.cppreference.com/mwiki/index.php?title=Template:cpp/memory/unique_ptr/dsc_operator_at&amp;action=edit" style="text-decoration:none; color:rgb(102,51,102); padding-top:0px!important; padding-right:13px; padding-bottom:0px!important; padding-left:0px!important" rel="nofollow">[编辑]</a></span></td> 
  </tr> 
 </tbody> 
</table>

### 非成员函数 ###

### 辅助类 ###

### 示例 ###

#include <iostream>
    #include <memory>
     
    struct Foo {
            
        Foo() {
             std::cout << "Foo::Foo\n"; }
        ~Foo() {
             std::cout << "Foo::~Foo\n"; }
        void bar() {
             std::cout << "Foo::bar\n"; }
    };
     
    void f(const Foo &foo)
    {
            
        std::cout << "f(const Foo&)\n";
    }
     
    int main()
    {
            
        std::unique_ptr<Foo> p1(new Foo);  // p1 拥有 Foo
        if (p1) p1->bar();
     
        {
            
            std::unique_ptr<Foo> p2(std::move(p1));  // 现在 p2 拥有 Foo
            f(*p2);
     
            p1 = std::move(p2);  // 所有权还给了 p1
            std::cout << "destroying p2...\n";
        }
     
        if (p1) p1->bar();
     
        // p1 离开作用域时， Foo 实例会自动销毁
    }

输出：

Foo::Foo
    Foo::bar
    f(const Foo&)
    destroying p2...
    Foo::bar
    Foo::~Foo

std::unique_ptr

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