C++ 智能指针详解

小鱼儿 2022-09-21 03:58 174阅读 0赞

**转载：http://blog.csdn.net/xt\_xiaotian/article/details/5714477**

**http://blog.jobbole.com/56316/**

**C++ 智能指针详解**

** **

**一、简介**

由于 C++ 语言没有自动内存回收机制，程序员每次 new 出来的内存都要手动 delete。程序员忘记 delete，流程太复杂，最终导致没有 delete，异常导致程序过早退出，没有执行 delete 的情况并不罕见。

用智能指针便可以有效缓解这类问题，本文主要讲解参见的智能指针的用法。包括：**std::auto\_ptr、boost::scoped\_ptr、boost::shared\_ptr、boost::scoped\_array、boost::shared\_array、boost::weak\_ptr、boost::intrusive\_ptr。**你可能会想，如此多的智能指针就为了解决new、delete匹配问题，真的有必要吗？看完这篇文章后，我想你心里自然会有答案。

下面就按照顺序讲解如上 7 种智能指针（smart\_ptr）。

**二、具体使用**

**1、总括**

对于编译器来说，智能指针实际上是一个栈对象，并非指针类型，在栈对象生命期即将结束时，智能指针通过析构函数释放有它管理的堆内存。所有智能指针都重载了“operator->”操作符，直接返回对象的引用，用以操作对象。访问智能指针原来的方法则使用“.”操作符。

访问智能指针包含的裸指针则可以用 get() 函数。由于智能指针是一个对象，所以if (my\_smart\_object)永远为真，要判断智能指针的裸指针是否为空，需要这样判断：if (my\_smart\_object.get())。

智能指针包含了 reset() 方法，如果不传递参数（或者传递 NULL），则智能指针会释放当前管理的内存。如果传递一个对象，则智能指针会释放当前对象，来管理新传入的对象。

我们编写一个测试类来辅助分析：

class Simple \{

public:

Simple(int param = 0) \{

number = param;

std::cout << "Simple: " << number << std::endl;

~Simple() \{

std::cout << "~Simple: " << number << std::endl;

void PrintSomething() \{

std::cout << "PrintSomething: " << info\_extend.c\_str() << std::endl;

std::string info\_extend;

int number;

\};

** **

**2、std::auto\_ptr**

std::auto\_ptr 属于 STL，当然在 namespace std 中，包含头文件 \#include<memory> 便可以使用。std::auto\_ptr 能够方便的管理单个堆内存对象。

我们从代码开始分析：

void TestAutoPtr() \{

std::auto\_ptr<Simple> my\_memory(new Simple(1));   // 创建对象，输出：Simple：1

if (my\_memory.get()) \{                            // 判断智能指针是否为空

my\_memory->PrintSomething();                    // 使用 operator-> 调用智能指针对象中的函数

my\_memory.get()->info\_extend = "Addition";      // 使用 get() 返回裸指针，然后给内部对象赋值

my\_memory->PrintSomething();                    // 再次打印，表明上述赋值成功

(\*my\_memory).info\_extend += " other";           // 使用 operator\* 返回智能指针内部对象，然后用“.”调用智能指针对象中的函数

my\_memory->PrintSomething();                    // 再次打印，表明上述赋值成功

\}                                                   // my\_memory 栈对象即将结束生命期，析构堆对象 Simple(1)

执行结果为：

Simple: 1

PrintSomething:

PrintSomething: Addition

PrintSomething: Addition other

~Simple: 1

上述为正常使用 std::auto\_ptr 的代码，一切似乎都良好，无论如何不用我们显示使用该死的delete 了。

其实好景不长，我们看看如下的另一个例子：

void TestAutoPtr2() \{

std::auto\_ptr<Simple> my\_memory(new Simple(1));

if (my\_memory.get()) \{

std::auto\_ptr<Simple> my\_memory2;   // 创建一个新的 my\_memory2 对象

my\_memory2 = my\_memory;             // 复制旧的 my\_memory 给 my\_memory2

my\_memory2->PrintSomething();       // 输出信息，复制成功

my\_memory->PrintSomething();        // 崩溃

最终如上代码导致崩溃，如上代码时绝对符合 C++ 编程思想的，居然崩溃了，跟进std::auto\_ptr 的源码后，我们看到，罪魁祸首是“my\_memory2 = my\_memory”，这行代码，my\_memory2 完全夺取了 my\_memory 的内存管理所有权，导致 my\_memory 悬空，最后使用时导致崩溃。

所以，使用 std::auto\_ptr 时，绝对不能使用“operator=”操作符。作为一个库，不允许用户使用，确没有明确拒绝\[1\]，多少会觉得有点出乎预料。

看完 std::auto\_ptr 好景不长的第一个例子后，让我们再来看一个：

void TestAutoPtr3() \{

std::auto\_ptr<Simple> my\_memory(new Simple(1));

if (my\_memory.get()) \{

my\_memory.release();

执行结果为：

Simple: 1

看到什么异常了吗？我们创建出来的对象没有被析构，没有输出“~Simple: 1”，导致内存泄露。当我们不想让 my\_memory 继续生存下去，我们调用 release() 函数释放内存，结果却导致内存泄露（在内存受限系统中，如果my\_memory占用太多内存，我们会考虑在使用完成后，立刻归还，而不是等到 my\_memory 结束生命期后才归还）。

正确的代码应该为：

void TestAutoPtr3() \{

std::auto\_ptr<Simple> my\_memory(new Simple(1));

if (my\_memory.get()) \{

Simple\* temp\_memory = my\_memory.release();

delete temp\_memory;

或

void TestAutoPtr3() \{

std::auto\_ptr<Simple> my\_memory(new Simple(1));

if (my\_memory.get()) \{

my\_memory.reset();  // 释放 my\_memory 内部管理的内存

原来 std::auto\_ptr 的 release() 函数只是让出内存所有权，这显然也不符合 C++ 编程思想。

总结：std::auto\_ptr 可用来管理单个对象的对内存，但是，请注意如下几点：

（1）    尽量不要使用“operator=”。如果使用了，请不要再使用先前对象。

（2）    记住 release() 函数不会释放对象，仅仅归还所有权。

（3）    std::auto\_ptr 最好不要当成参数传递（读者可以自行写代码确定为什么不能）。

（4）    由于 std::auto\_ptr 的“operator=”问题，有其管理的对象不能放入 std::vector 等容器中。

（5）    ……

使用一个 std::auto\_ptr 的限制还真多，还不能用来管理堆内存数组，这应该是你目前在想的事情吧，我也觉得限制挺多的，哪天一个不小心，就导致问题了。

由于 std::auto\_ptr 引发了诸多问题，一些设计并不是非常符合 C++ 编程思想，所以引发了下面 boost 的智能指针，boost 智能指针可以解决如上问题。

让我们继续向下看。

**3、boost::scoped\_ptr**

boost::scoped\_ptr 属于 boost 库，定义在 namespace boost 中，包含头文件\#include<boost/smart\_ptr.hpp> 便可以使用。boost::scoped\_ptr 跟 std::auto\_ptr 一样，可以方便的管理单个堆内存对象，特别的是，boost::scoped\_ptr 独享所有权，避免了 std::auto\_ptr恼人的几个问题。

我们还是从代码开始分析：

void TestScopedPtr() \{

boost::scoped\_ptr<Simple> my\_memory(new Simple(1));

if (my\_memory.get()) \{

my\_memory->PrintSomething();

my\_memory.get()->info\_extend = "Addition";

my\_memory->PrintSomething();

(\*my\_memory).info\_extend += " other";

my\_memory->PrintSomething();

my\_memory.release();           // 编译 error: scoped\_ptr 没有 release 函数

std::auto\_ptr<Simple> my\_memory2;

my\_memory2 = my\_memory;        // 编译 error: scoped\_ptr 没有重载 operator=，不会导致所有权转移

首先，我们可以看到，boost::scoped\_ptr 也可以像 auto\_ptr 一样正常使用。但其没有release() 函数，不会导致先前的内存泄露问题。其次，由于 boost::scoped\_ptr 是独享所有权的，所以明确拒绝用户写“my\_memory2 = my\_memory”之类的语句，可以缓解 std::auto\_ptr 几个恼人的问题。

由于 boost::scoped\_ptr 独享所有权，当我们真真需要复制智能指针时，需求便满足不了了，如此我们再引入一个智能指针，专门用于处理复制，参数传递的情况，这便是如下的boost::shared\_ptr。

**4、boost::shared\_ptr**

boost::shared\_ptr 属于 boost 库，定义在 namespace boost 中，包含头文件\#include<boost/smart\_ptr.hpp> 便可以使用。在上面我们看到 boost::scoped\_ptr 独享所有权，不允许赋值、拷贝，boost::shared\_ptr 是专门用于共享所有权的，由于要共享所有权，其在内部使用了引用计数。boost::shared\_ptr 也是用于管理单个堆内存对象的。

我们还是从代码开始分析：

void TestSharedPtr(boost::shared\_ptr<Simple> memory) \{   // 注意：无需使用 reference (或 const reference)

memory->PrintSomething();

std::cout << "TestSharedPtr UseCount: " << memory.use\_count() << std::endl;

void TestSharedPtr2() \{

boost::shared\_ptr<Simple> my\_memory(new Simple(1));

if (my\_memory.get()) \{

my\_memory->PrintSomething();

my\_memory.get()->info\_extend = "Addition";

my\_memory->PrintSomething();

(\*my\_memory).info\_extend += " other";

my\_memory->PrintSomething();

std::cout << "TestSharedPtr2 UseCount: " << my\_memory.use\_count() << std::endl;

TestSharedPtr(my\_memory);

std::cout << "TestSharedPtr2 UseCount: " << my\_memory.use\_count() << std::endl;

//my\_memory.release();// 编译 error: 同样，shared\_ptr 也没有 release 函数

执行结果为：

Simple: 1

PrintSomething:

PrintSomething: Addition

PrintSomething: Addition other

TestSharedPtr2 UseCount: 1

PrintSomething: Addition other

TestSharedPtr UseCount: 2

TestSharedPtr2 UseCount: 1

~Simple: 1

boost::shared\_ptr 也可以很方便的使用。并且没有 release() 函数。关键的一点，boost::shared\_ptr 内部维护了一个引用计数，由此可以支持复制、参数传递等。boost::shared\_ptr 提供了一个函数 use\_count() ，此函数返回 boost::shared\_ptr 内部的引用计数。查看执行结果，我们可以看到在 TestSharedPtr2 函数中，引用计数为 1，传递参数后（此处进行了一次复制），在函数TestSharedPtr 内部，引用计数为2，在 TestSharedPtr 返回后，引用计数又降低为 1。当我们需要使用一个共享对象的时候，boost::shared\_ptr 是再好不过的了。

在此，我们已经看完单个对象的智能指针管理，关于智能指针管理数组，我们接下来讲到。

**5、boost::scoped\_array**

boost::scoped\_array 属于 boost 库，定义在 namespace boost 中，包含头文件\#include<boost/smart\_ptr.hpp> 便可以使用。

boost::scoped\_array 便是用于管理动态数组的。跟 boost::scoped\_ptr 一样，也是独享所有权的。

我们还是从代码开始分析：

void TestScopedArray() \{

boost::scoped\_array<Simple> my\_memory(new Simple\[2\]); // 使用内存数组来初始化

if (my\_memory.get()) \{

my\_memory\[0\].PrintSomething();

my\_memory.get()\[0\].info\_extend = "Addition";

my\_memory\[0\].PrintSomething();

(\*my\_memory)\[0\].info\_extend += " other";            // 编译 error，scoped\_ptr 没有重载 operator\*

my\_memory\[0\].release();                             // 同上，没有release 函数

boost::scoped\_array<Simple> my\_memory2;

my\_memory2 = my\_memory;                             // 编译error，同上，没有重载 operator=

boost::scoped\_array 的使用跟 boost::scoped\_ptr 差不多，不支持复制，并且初始化的时候需要使用动态数组。另外，boost::scoped\_array 没有重载“operator\*”，其实这并无大碍，一般情况下，我们使用 get() 函数更明确些。

下面肯定应该讲 boost::shared\_array 了，一个用引用计数解决复制、参数传递的智能指针类。

**6、boost::shared\_array**

boost::shared\_array 属于 boost 库，定义在 namespace boost 中，包含头文件\#include<boost/smart\_ptr.hpp> 便可以使用。

由于 boost::scoped\_array 独享所有权，显然在很多情况下（参数传递、对象赋值等）不满足需求，由此我们引入 boost::shared\_array。跟 boost::shared\_ptr 一样，内部使用了引用计数。

我们还是从代码开始分析：

void TestSharedArray(boost::shared\_array<Simple> memory) \{  // 注意：无需使用 reference (或 const reference)

std::cout << "TestSharedArray UseCount: " << memory.use\_count() << std::endl;

void TestSharedArray2() \{

boost::shared\_array<Simple> my\_memory(new Simple\[2\]);

if (my\_memory.get()) \{

my\_memory\[0\].PrintSomething();

my\_memory.get()\[0\].info\_extend = "Addition 00";

my\_memory\[0\].PrintSomething();

my\_memory\[1\].PrintSomething();

my\_memory.get()\[1\].info\_extend = "Addition 11";

my\_memory\[1\].PrintSomething();

//(\*my\_memory)\[0\].info\_extend += " other";  // 编译 error，scoped\_ptr 没有重载 operator\*

std::cout << "TestSharedArray2 UseCount: " << my\_memory.use\_count() << std::endl;

TestSharedArray(my\_memory);

std::cout << "TestSharedArray2 UseCount: " << my\_memory.use\_count() << std::endl;

执行结果为：

Simple: 0

PrintSomething:

PrintSomething: Addition 00

PrintSomething:

PrintSomething: Addition 11

TestSharedArray2 UseCount: 1

TestSharedArray UseCount: 2

TestSharedArray2 UseCount: 1

~Simple: 0

跟 boost::shared\_ptr 一样，使用了引用计数，可以复制，通过参数来传递。

至此，我们讲过的智能指针有std::auto\_ptr、boost::scoped\_ptr、boost::shared\_ptr、boost::scoped\_array、boost::shared\_array。这几个智能指针已经基本够我们使用了，90% 的使用过标准智能指针的代码就这 5 种。可如下还有两种智能指针，它们肯定有用，但有什么用处呢，一起看看吧。

**7、boost::weak\_ptr**

boost::weak\_ptr 属于 boost 库，定义在 namespace boost 中，包含头文件\#include<boost/smart\_ptr.hpp> 便可以使用。

在讲 boost::weak\_ptr 之前，让我们先回顾一下前面讲解的内容。似乎boost::scoped\_ptr、boost::shared\_ptr 这两个智能指针就可以解决所有单个对象内存的管理了，这儿还多出一个 boost::weak\_ptr，是否还有某些情况我们没纳入考虑呢？

回答：有。首先 boost::weak\_ptr 是专门为 boost::shared\_ptr 而准备的。有时候，我们只关心能否使用对象，并不关心内部的引用计数。boost::weak\_ptr 是 boost::shared\_ptr 的观察者（Observer）对象，观察者意味着 boost::weak\_ptr 只对 boost::shared\_ptr 进行引用，而不改变其引用计数，当被观察的 boost::shared\_ptr 失效后，相应的 boost::weak\_ptr 也相应失效。

我们还是从代码开始分析：

void TestWeakPtr() \{

boost::weak\_ptr<Simple> my\_memory\_weak;

boost::shared\_ptr<Simple> my\_memory(new Simple(1));

std::cout << "TestWeakPtr boost::shared\_ptr UseCount: " << my\_memory.use\_count() << std::endl;

my\_memory\_weak = my\_memory;

std::cout << "TestWeakPtr boost::shared\_ptr UseCount: " << my\_memory.use\_count() << std::endl;

执行结果为：

Simple: 1

TestWeakPtr boost::shared\_ptr UseCount: 1

~Simple: 1

我们看到，尽管被赋值了，内部的引用计数并没有什么变化，当然，读者也可以试试传递参数等其他情况。

现在要说的问题是，boost::weak\_ptr 到底有什么作用呢？从上面那个例子看来，似乎没有任何作用，其实 boost::weak\_ptr 主要用在软件架构设计中，可以在基类（此处的基类并非抽象基类，而是指继承于抽象基类的虚基类）中定义一个 boost::weak\_ptr，用于指向子类的boost::shared\_ptr，这样基类仅仅观察自己的 boost::weak\_ptr 是否为空就知道子类有没对自己赋值了，而不用影响子类 boost::shared\_ptr 的引用计数，用以降低复杂度，更好的管理对象。

**    8、boost::intrusive\_ptr**

boost::intrusive\_ptr属于 boost 库，定义在 namespace boost 中，包含头文件\#include<boost/smart\_ptr.hpp> 便可以使用。

讲完如上 6 种智能指针后，对于一般程序来说 C++ 堆内存管理就够用了，现在有多了一种boost::intrusive\_ptr，这是一种插入式的智能指针，内部不含有引用计数，需要程序员自己加入引用计数，不然编译不过（⊙﹏⊙b汗）。个人感觉这个智能指针没太大用处，至少我没用过。有兴趣的朋友自己研究一下源代码哦J。

**三、总结**

如上讲了这么多智能指针，有必要对这些智能指针做个总结：

1、在可以使用 boost 库的场合下，拒绝使用 std::auto\_ptr，因为其不仅不符合 C++ 编程思想，而且极容易出错\[2\]。

2、在确定对象无需共享的情况下，使用 boost::scoped\_ptr（当然动态数组使用boost::scoped\_array）。

3、在对象需要共享的情况下，使用 boost::shared\_ptr（当然动态数组使用boost::shared\_array）。

4、在需要访问 boost::shared\_ptr 对象，而又不想改变其引用计数的情况下，使用boost::weak\_ptr，一般常用于软件框架设计中。

5、最后一点，也是要求最苛刻一点：在你的代码中，不要出现 delete 关键字（或 C 语言的free 函数），因为可以用智能指针去管理。

\---------------------------------------

\[1\]参见《effective C++（3rd）》，条款06 。

\[2\]关于 boost 库的使用，可本博客另外一篇文章：《在 Windows 中编译 boost1.42.0》。

\[3\]读者应该看到了，在我所有的名字前，都加了命名空间标识符std::（或boost::），这不是我不想写 using namespace XXX 之类的语句，在大型项目中，有可能会用到 N 个第三方库，如果把命名空间全放出来，命名污染（Naming conflicts）问题很难避免，到时要改回来是极端麻烦的事情。当然，如果你只是写 Demo，可以例外。

在C++中，我们通过new（在动态内存中为对象分配空间并初始化对象）和delete（销毁该对象，并释放内存）直接分配和释放动态内存。

如下代码：

C++

有些人有这样的疑问，指针一定要new吗？其实指针和new没有什么关系。这里的new在动态内存里为对象分配了内存空间，并返回了一个指向该对象的指针。new是申请堆空间，不是在栈上分配内存，指针只要指向有效的内存空间就可以。比如：

C++

new直接初始化对

象：

C++

new分配const对象必须进行初始化，并且返回的是一个指向const对象的指针：

C++

当然new申请内存分配的时候也不是都会成功的，一旦一个程序用光了他的所有可用内存（虽然这种情况一般很少发生），new表达式就会失败。这时候会抛出bad\_alloc异常。所以我们需要通过delete来释放占用的内存。在这里注意delete并不是要删除指针，而是释放指针所指的内存。

C++

使用new和delete来管理动态内存常出的一些错误：

1.忘记delete，即导致了“内存泄漏”，

2.野指针。在对象已经被释放掉之后，（这里注意，此时的指针成为了悬垂指针，即指向曾经存在的对象，但该对象已经不再存在。结果未定义，而且难以检测。）这时候我们再次使用，会产生使用非法内存的指针。

不过如果我们需要保留指针，可以在delete以后将nullptr赋予指针，这样指针就不指向任何对象了，如下代码：

C++

题外话：在测试这个问题的时候，我输出了下q的值发现还是42，并且没有报错，后来在delete p之后，我又给\*p = 19;这个时候 p ,q的值在输出的时候都是19，也没有报错。这个代码其实根本就是错误的了，因为p,q已经没有有效的内存空间了。这里是释放了内存，但指针的值不变，指向的内存不会清0，指向的这片内存区域是待分配的，如果没有被其他数据覆盖的话，你就能幸运得输出这主要原因是你分配的内存小，没有继续分配，被占用的概率小所致。我用的xcode，换到VS下就正常报错了，是因为VS为了从编译器的角度上解决缓冲区溢出等问题，加上的这种功能，C++标准里面没有这么要求，所有xcode和gcc是不会检查的。所以在这里 建议大家写纯C++代码的时候用vs。

3.重复delete，就会使自由空间遭到破坏如：

C++

虽然显示的管理内存在性能上有一定的优势，但是随着多线程程序的出现和广泛使用，内存管理不佳的的情况变得更严重。所以C++标准库中的智能指针很好的解决了这些问题。

auto\_ptr以对象的方式管理堆分配的内存，并在适当的时间（比如析构），释放内存。我们只需要将new操作返回的指针作为auto\_ptr的初始值，而不需要调用delete：

C++

但是auto\_ptr在拷贝时会返回一个左值并且不能调用delete\[\];所以在C++11中改用shared\_ptr(允许多个指针指向一个对象),unique\_ptr（“独占”所指向的对象）还有weak\_ptr它是一种不控制所指对象生存期的智能指针，指向shared\_ptr所管理的对像，在memory头文件中。

C++

如下代码：

C++

当然我们也可以shared\_ptr和new来结合使用，但是必须使用直接初始化的形式来初始化一个智能指针，

C++

但是最好不要混合使用普通指针和智能指针，最安全的分配和使用动态内存的方法是调用make\_shared的标准库函数。在使用它的时候，必须指定想要创建的对象类型。

C++

如果我们不传递任何参数，对象会进行值初始化

C++

shared\_ptr 实现了引用计数型的智能指针，当进行拷贝的时候，计数器都会递增。而对一个对象进行赋值时，赋值操作符减少左操作数所指对象的引用计数（减1，如果引用计数为减至0，则删除对象），并增加右操作数所指对象的引用计数（加1），如下代码：

C++

此时r的引用技术为0，r原指对象被自动释放。q的引用计数增加。

weak\_ptr的使用和析构都不会改变shared\_ptr的引用计数。weak\_ptr可以使用一个非常重要的成员函数lock()从被观测的shared\_ptr获得一个可用的shared\_ptr对象， 从而操作资源。但当expired()==true的时候，lock()函数将返回一个存储空指针的shared\_ptr.如下：

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   <td style="font-size: 13px; text-align: center; width: 581px; border: none !important; margin: 0px !important; padding: 0px !important; vertical-align: top !important; font-family: Monaco, MonacoRegular, 'Courier New', monospace !important; background: none;"> 
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      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
     </div> 
     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;">
       &nbsp; 
      <span style="border: 0px; margin: 0px; padding: 0px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: bold !important;">assert</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">(</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">sp</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">.</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: teal !important;">use_count</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">(</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">)</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">==</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 153, 153) !important;">1</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">)</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
     </div> 
     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;">
       &nbsp; 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">weak_ptr</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&amp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">lt</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: bold !important; color: rgb(128, 0, 128) !important;">int</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&amp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">gt</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: teal !important;">wp</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">(</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">sp</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">)</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(153, 153, 153) !important; font-style: italic !important;">//从shared_ptr创建weak_ptr</span> 
     </div> 
     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;">
       &nbsp; 
      <span style="border: 0px; margin: 0px; padding: 0px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: bold !important;">assert</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">(</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">wp</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">.</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: teal !important;">use_count</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">(</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">)</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">==</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 153, 153) !important;">1</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">)</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
     </div> 
     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;">
       &nbsp; 
      <span style="border: 0px; margin: 0px; padding: 0px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: bold !important;">if</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">(</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">!</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">wp</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">.</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: teal !important;">expired</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">(</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">)</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">)</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(153, 153, 153) !important; font-style: italic !important;">//判断weak_ptr观察的对象是否失效</span> 
     </div> 
     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;">
       &nbsp; 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">{ </span> 
     </div> 
     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;">
       &nbsp;&nbsp; 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">shared_ptr</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&amp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">lt</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: bold !important; color: rgb(128, 0, 128) !important;">int</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">&amp;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">gt</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">sp2</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">=</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">wp</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">.</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: teal !important;">lock</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">(</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">)</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(153, 153, 153) !important; font-style: italic !important;">//获得一个shared_ptr</span> 
     </div> 
     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;">
       &nbsp;&nbsp; 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">*</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">sp2</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">=</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 153, 153) !important;">100</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
     </div> 
     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;">
       &nbsp;&nbsp; 
      <span style="border: 0px; margin: 0px; padding: 0px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: bold !important;">assert</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">(</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">wp</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">.</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: teal !important;">use_count</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">(</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">)</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">==</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 153, 153) !important;">2</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">)</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
     </div> 
     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;">
       &nbsp; 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">}</span> 
     </div> 
     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;">
       &nbsp; 
      <span style="border: 0px; margin: 0px; padding: 0px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: bold !important;">assert</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">(</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 45, 122) !important;">wp</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">.</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: teal !important;">use_count</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">(</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">)</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;">==</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 153, 153) !important;">1</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">)</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
     </div> 
     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;">
       &nbsp; 
      <span style="border: 0px; margin: 0px; padding: 0px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: bold !important;">return</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 111, 224) !important;"> </span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(0, 153, 153) !important;">0</span> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">;</span> 
     </div> 
     <div style="border: none; margin: 0px; padding: 0px 5px; font-family: inherit; height: inherit; font-size: inherit !important; line-height: inherit !important; font-weight: inherit !important; background: none;"> 
      <span style="border: 0px; margin: 0px; padding: 0px; font-size: inherit !important; font-family: inherit; height: inherit; line-height: inherit !important; font-weight: inherit !important; color: rgb(51, 51, 51) !important;">}</span> 
     </div> 
    </div></td> 
  </tr> 
 </tbody> 
</table>

当我们定义一个unique\_ptr的时候，需要将其绑定到一个new返回的指针。

只能有一个uniqu\_ptr指向对象，也就是说它不能被拷贝，也不支持赋值。但是我们可以通过move来移动

C++