lambda 表达式 c++

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本文章为转载文章，原地址不晓得了，

然后个人觉得c++中lambda表达式和函数指针的作用是一样的，虽然优化了代码方式，可能是不适应的原因吧，总感觉看起来比较别扭。。。。

很多高级语言里引入了lambda表达式的概念，即匿名函数。以往C++需要传入一个函数的时候，必须事先进行声明，视情况可以声明为一个普通函数然后传入函数指针，或者声明一个funtor，然后传入一个对象。

但这种传统方法太过复杂，一个简单的遍历输出就需要声明一个类或者函数，本来用于简化语法的东西却使语法大大复杂化。

比如一个用随机数填充数组的例子：

<span class="com" style="font-family: Arial, Helvetica, sans-serif; color: rgb(136, 0, 0);">#include</span><span class="pln" style="font-family: Arial, Helvetica, sans-serif; color: rgb(0, 0, 0);"> </span><span class="str" style="font-family: Arial, Helvetica, sans-serif; color: rgb(0, 136, 0);"><iostream></span>

<span class="com" style="color: rgb(136, 0, 0);">#include</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="str" style="color: rgb(0, 136, 0);"><cstdlib></span><span class="pln" style="color: rgb(0, 0, 0);"></span><span class="com" style="color: rgb(136, 0, 0);">#include</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="str" style="color: rgb(0, 136, 0);"><iterator></span><span class="pln" style="color: rgb(0, 0, 0);"></span><span class="com" style="color: rgb(136, 0, 0);">#include</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="str" style="color: rgb(0, 136, 0);"><algorithm></span><span class="pln" style="color: rgb(0, 0, 0);"></span><span class="kwd" style="color: rgb(0, 0, 136);">using</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="kwd" style="color: rgb(0, 0, 136);">namespace</span><span class="pln" style="color: rgb(0, 0, 0);"> std</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln" style="color: rgb(0, 0, 0);"></span><span class="kwd" style="color: rgb(0, 0, 136);">class</span><span class="pln" style="color: rgb(0, 0, 0);"> mi_rand</span><span class="pun" style="color: rgb(102, 102, 0);">{</span><span class="pln" style="color: rgb(0, 0, 0);">    </span><span class="kwd" style="color: rgb(0, 0, 136);">public</span><span class="pun" style="color: rgb(102, 102, 0);">:</span><span class="pln" style="color: rgb(0, 0, 0);">        mi_rand </span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln" style="color: rgb(0, 0, 0);"> start_pos</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln" style="color: rgb(0, 0, 0);"> end_pos</span><span class="pun" style="color: rgb(102, 102, 0);">)</span><span class="pln" style="color: rgb(0, 0, 0);">        </span><span class="pun" style="color: rgb(102, 102, 0);">:</span><span class="pln" style="color: rgb(0, 0, 0);"> a</span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="pln" style="color: rgb(0, 0, 0);">start_pos</span><span class="pun" style="color: rgb(102, 102, 0);">),</span><span class="pln" style="color: rgb(0, 0, 0);"> b</span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="pln" style="color: rgb(0, 0, 0);">end_pos</span><span class="pun" style="color: rgb(102, 102, 0);">)</span><span class="pln" style="color: rgb(0, 0, 0);">         </span><span class="pun" style="color: rgb(102, 102, 0);">{}</span><span class="pln" style="color: rgb(0, 0, 0);">        </span><span class="kwd" style="color: rgb(0, 0, 136);">unsigned</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="kwd" style="color: rgb(0, 0, 136);">operator</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">()</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">()</span><span class="pln" style="color: rgb(0, 0, 0);">         </span><span class="pun" style="color: rgb(102, 102, 0);">{</span><span class="pln" style="color: rgb(0, 0, 0);">            </span><span class="kwd" style="color: rgb(0, 0, 136);">return</span><span class="pln" style="color: rgb(0, 0, 0);"> rand</span><span class="pun" style="color: rgb(102, 102, 0);">()</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">%</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="pln" style="color: rgb(0, 0, 0);">b</span><span class="pun" style="color: rgb(102, 102, 0);">-</span><span class="pln" style="color: rgb(0, 0, 0);">a</span><span class="pun" style="color: rgb(102, 102, 0);">+</span><span class="lit" style="color: rgb(0, 102, 102);">1</span><span class="pun" style="color: rgb(102, 102, 0);">)</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">+</span><span class="pln" style="color: rgb(0, 0, 0);"> a</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln" style="color: rgb(0, 0, 0);">        </span><span class="pun" style="color: rgb(102, 102, 0);">}</span><span class="pln" style="color: rgb(0, 0, 0);">    </span><span class="kwd" style="color: rgb(0, 0, 136);">private</span><span class="pun" style="color: rgb(102, 102, 0);">:</span><span class="pln" style="color: rgb(0, 0, 0);">        </span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln" style="color: rgb(0, 0, 0);"> a</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln" style="color: rgb(0, 0, 0);"> b</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln" style="color: rgb(0, 0, 0);"></span><span class="pun" style="color: rgb(102, 102, 0);">};</span><span class="pln" style="color: rgb(0, 0, 0);"></span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln" style="color: rgb(0, 0, 0);"> main</span><span class="pun" style="color: rgb(102, 102, 0);">()</span><span class="pln" style="color: rgb(0, 0, 0);"></span><span class="pun" style="color: rgb(102, 102, 0);">{</span><span class="pln" style="color: rgb(0, 0, 0);">    </span><span class="kwd" style="color: rgb(0, 0, 136);">const</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln" style="color: rgb(0, 0, 0);"> SIZE </span><span class="pun" style="color: rgb(102, 102, 0);">=</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="lit" style="color: rgb(0, 102, 102);">20</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln" style="color: rgb(0, 0, 0);">    </span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln" style="color: rgb(0, 0, 0);"> array</span><span class="pun" style="color: rgb(102, 102, 0);">[</span><span class="pln" style="color: rgb(0, 0, 0);">SIZE</span><span class="pun" style="color: rgb(102, 102, 0);">];</span><span class="pln" style="color: rgb(0, 0, 0);">    generate_n </span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="pln" style="color: rgb(0, 0, 0);">array</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln" style="color: rgb(0, 0, 0);"> SIZE</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln" style="color: rgb(0, 0, 0);"> mi_rand </span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="lit" style="color: rgb(0, 102, 102);">1</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="lit" style="color: rgb(0, 102, 102);">30</span><span class="pun" style="color: rgb(102, 102, 0);">));</span><span class="pln" style="color: rgb(0, 0, 0);">        copy </span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="pln" style="color: rgb(0, 0, 0);">array</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln" style="color: rgb(0, 0, 0);"> array </span><span class="pun" style="color: rgb(102, 102, 0);">+</span><span class="pln" style="color: rgb(0, 0, 0);"> SIZE</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln" style="color: rgb(0, 0, 0);">           ostream_iterator</span><span class="str" style="color: rgb(0, 136, 0);"><int></span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="pln" style="color: rgb(0, 0, 0);">cout</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="str" style="color: rgb(0, 136, 0);">" "</span><span class="pun" style="color: rgb(102, 102, 0);">));</span><span class="pln" style="color: rgb(0, 0, 0);">    cout </span><span class="pun" style="color: rgb(102, 102, 0);"><<</span><span class="pln" style="color: rgb(0, 0, 0);"> endl</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln" style="color: rgb(0, 0, 0);">        </span><span class="kwd" style="color: rgb(0, 0, 136);">return</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="lit" style="color: rgb(0, 102, 102);">0</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln" style="color: rgb(0, 0, 0);"></span><span class="pun" style="color: rgb(102, 102, 0);">}</span>

示例中，generate_n的目的是使填充数组的操作简单化，但为了这种简单化却要额外声明一个类。输出数组时利用STL的确能进行语法上的简化，但是这种简化却要求对STL非常了解，而且拓展性非常差。

所幸，在c++0x标准中终于引入了lambda表达式，目前 VS 2010 和 g++ 4.5 已经进行了试验性的实现。针对上面的填充和输出操作，下面是使用lambda表达式的简化版：

<span class="com" style="color: rgb(136, 0, 0);">#include</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="str" style="color: rgb(0, 136, 0);"><iostream></span><span class="pln" style="color: rgb(0, 0, 0);"></span><span class="com" style="color: rgb(136, 0, 0);">#include</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="str" style="color: rgb(0, 136, 0);"><cstdlib></span><span class="pln" style="color: rgb(0, 0, 0);"></span><span class="com" style="color: rgb(136, 0, 0);">#include</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="str" style="color: rgb(0, 136, 0);"><algorithm></span><span class="pln" style="color: rgb(0, 0, 0);"></span><span class="kwd" style="color: rgb(0, 0, 136);">using</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="kwd" style="color: rgb(0, 0, 136);">namespace</span><span class="pln" style="color: rgb(0, 0, 0);"> std</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln" style="color: rgb(0, 0, 0);"></span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln" style="color: rgb(0, 0, 0);"> main</span><span class="pun" style="color: rgb(102, 102, 0);">()</span><span class="pln" style="color: rgb(0, 0, 0);"></span><span class="pun" style="color: rgb(102, 102, 0);">{</span><span class="pln" style="color: rgb(0, 0, 0);">    </span><span class="kwd" style="color: rgb(0, 0, 136);">const</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln" style="color: rgb(0, 0, 0);"> SIZE </span><span class="pun" style="color: rgb(102, 102, 0);">=</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="lit" style="color: rgb(0, 102, 102);">20</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln" style="color: rgb(0, 0, 0);">    </span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln" style="color: rgb(0, 0, 0);"> array</span><span class="pun" style="color: rgb(102, 102, 0);">[</span><span class="pln" style="color: rgb(0, 0, 0);">SIZE</span><span class="pun" style="color: rgb(102, 102, 0);">];</span><span class="pln" style="color: rgb(0, 0, 0);">    generate_n </span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="pln" style="color: rgb(0, 0, 0);">array</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln" style="color: rgb(0, 0, 0);"> SIZE</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln" style="color: rgb(0, 0, 0);">                </span><span class="pun" style="color: rgb(102, 102, 0);">[]</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">()</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">{</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="kwd" style="color: rgb(0, 0, 136);">return</span><span class="pln" style="color: rgb(0, 0, 0);"> rand</span><span class="pun" style="color: rgb(102, 102, 0);">()</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">%</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="lit" style="color: rgb(0, 102, 102);">30</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">+</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="lit" style="color: rgb(0, 102, 102);">1</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">});</span><span class="pln" style="color: rgb(0, 0, 0);">    for_each </span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="pln" style="color: rgb(0, 0, 0);">array</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln" style="color: rgb(0, 0, 0);"> array </span><span class="pun" style="color: rgb(102, 102, 0);">+</span><span class="pln" style="color: rgb(0, 0, 0);"> SIZE</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln" style="color: rgb(0, 0, 0);">               </span><span class="pun" style="color: rgb(102, 102, 0);">[]</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln" style="color: rgb(0, 0, 0);"> a</span><span class="pun" style="color: rgb(102, 102, 0);">){</span><span class="pln" style="color: rgb(0, 0, 0);"> cout </span><span class="pun" style="color: rgb(102, 102, 0);"><<</span><span class="pln" style="color: rgb(0, 0, 0);"> a </span><span class="pun" style="color: rgb(102, 102, 0);"><<</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="str" style="color: rgb(0, 136, 0);">" "</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">});</span><span class="pln" style="color: rgb(0, 0, 0);">        </span><span class="kwd" style="color: rgb(0, 0, 136);">return</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="lit" style="color: rgb(0, 102, 102);">0</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln" style="color: rgb(0, 0, 0);"></span><span class="pun" style="color: rgb(102, 102, 0);">}</span><span class="pln" style="color: rgb(0, 0, 0);"></span>

编译时需要注意的是，VS要求版本在2010以上，编译时需要加上 /EHsc 参数。使用g++编译的话版本要在版本4.5以上，并加上 --std=c++0x 参数。

g++目前（10年八月）的最新版本为4.51，你可以到 http://gcc.gnu.org/自行下载编译。ubuntu下可以通过 PPA for Ubuntu Toolchain Hackers直接安装二进制版本。

下面将阐述lambda表达式的语法，内容主要参考自 Lambda Expression Syntax。

如图，lambda表达式由下面几个部分构成：

lambda-introducer （捕获字段）
lambda-parameter-declaration-list （变量列表）
mutable-specification （捕获的变量可否修改）
exception-specification （异常设定）
lambda-return-type-clause （返回类型）
compound-statement （函数体）

外部变量的捕获规则

默认情况下，即捕获字段为 [] 时，lambda表达式是不能访问任何外部变量的，即表达式的函数体内无法访问当前作用域下的变量。

如果要设定表达式能够访问外部变量，可以在 [] 内写入 & 或者 = 加上变量名，其中 & 表示按引用访问，= 表示按值访问，变量之间用逗号分隔，比如 [=factor, &total] 表示按值访问变量 factor，而按引用访问 total。

不加变量名时表示设置默认捕获字段，外部变量将按照默认字段获取，后面在书写变量名时不加符号表示按默认字段设置，比如下面三条字段都是同一含义：

<span class="pun" style="color: rgb(102, 102, 0);">[&</span><span class="pln" style="color: rgb(0, 0, 0);">total</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln" style="color: rgb(0, 0, 0);"> factor</span><span class="pun" style="color: rgb(102, 102, 0);">]</span><span class="pln" style="color: rgb(0, 0, 0);"></span><span class="pun" style="color: rgb(102, 102, 0);">[&,</span><span class="pln" style="color: rgb(0, 0, 0);"> factor</span><span class="pun" style="color: rgb(102, 102, 0);">]</span><span class="pln" style="color: rgb(0, 0, 0);"></span><span class="pun" style="color: rgb(102, 102, 0);">[=,</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">&</span><span class="pln" style="color: rgb(0, 0, 0);">total</span><span class="pun" style="color: rgb(102, 102, 0);">]</span>

参数列表

lambda表达式的参数列表基本和函数的一致，不过有如下限制：

参数列表不能有默认参数
不能是可变参数列表
所有的参数必须有个变量名

如果你不提供 mutable-specification, exception-specification, 以及 lambda-return-type-clause，参数列表是也可以省略的。如下面的表达式：

<span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln" style="color: rgb(0, 0, 0);"> main</span><span class="pun" style="color: rgb(102, 102, 0);">()</span><span class="pln" style="color: rgb(0, 0, 0);"></span><span class="pun" style="color: rgb(102, 102, 0);">{</span><span class="pln" style="color: rgb(0, 0, 0);">   </span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln" style="color: rgb(0, 0, 0);"> x </span><span class="pun" style="color: rgb(102, 102, 0);">=</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="lit" style="color: rgb(0, 102, 102);">4</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln" style="color: rgb(0, 0, 0);">   </span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln" style="color: rgb(0, 0, 0);"> y </span><span class="pun" style="color: rgb(102, 102, 0);">=</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="lit" style="color: rgb(0, 102, 102);">5</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln" style="color: rgb(0, 0, 0);">   </span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln" style="color: rgb(0, 0, 0);"> z </span><span class="pun" style="color: rgb(102, 102, 0);">=</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">[=]</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">{</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="kwd" style="color: rgb(0, 0, 136);">return</span><span class="pln" style="color: rgb(0, 0, 0);"> x </span><span class="pun" style="color: rgb(102, 102, 0);">+</span><span class="pln" style="color: rgb(0, 0, 0);"> y</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">}();</span><span class="pln" style="color: rgb(0, 0, 0);"></span><span class="pun" style="color: rgb(102, 102, 0);">}</span>

能否修改捕获的变量

如果在参数列表后加上了 mutable，则表示表达式可以修改按值捕获的外部变量的拷贝。

异常设置

和函数一样，可以用 throw 来限定表达式能够抛出哪些异常。

返回类型

如果设置返回类型，你需要在类型名前面加上 ->。如果你只有一个返回语句的话，返回类型可以省略，编译器将会为你做出判断。

函数体

lambda表达式的函数体和普通函数大致相同。

下面是lambda表达式的几个完整例子：

<span class="com" style="color: rgb(136, 0, 0);">#include</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="str" style="color: rgb(0, 136, 0);"><algorithm></span><span class="pln" style="color: rgb(0, 0, 0);"></span><span class="com" style="color: rgb(136, 0, 0);">#include</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="str" style="color: rgb(0, 136, 0);"><iostream></span><span class="pln" style="color: rgb(0, 0, 0);"></span><span class="com" style="color: rgb(136, 0, 0);">#include</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="str" style="color: rgb(0, 136, 0);"><vector></span><span class="pln" style="color: rgb(0, 0, 0);"></span><span class="kwd" style="color: rgb(0, 0, 136);">using</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="kwd" style="color: rgb(0, 0, 136);">namespace</span><span class="pln" style="color: rgb(0, 0, 0);"> std</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln" style="color: rgb(0, 0, 0);"></span><span class="com" style="color: rgb(136, 0, 0);">// The number of elements in the vector.</span><span class="pln" style="color: rgb(0, 0, 0);"></span><span class="kwd" style="color: rgb(0, 0, 136);">const</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln" style="color: rgb(0, 0, 0);"> elementCount </span><span class="pun" style="color: rgb(102, 102, 0);">=</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="lit" style="color: rgb(0, 102, 102);">9</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln" style="color: rgb(0, 0, 0);"></span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln" style="color: rgb(0, 0, 0);"> main</span><span class="pun" style="color: rgb(102, 102, 0);">()</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">{</span><span class="pln" style="color: rgb(0, 0, 0);">   </span><span class="com" style="color: rgb(136, 0, 0);">// Create a vector object with each element set to 1.</span><span class="pln" style="color: rgb(0, 0, 0);">   vector</span><span class="str" style="color: rgb(0, 136, 0);"><int></span><span class="pln" style="color: rgb(0, 0, 0);"> v</span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="pln" style="color: rgb(0, 0, 0);">elementCount</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="lit" style="color: rgb(0, 102, 102);">1</span><span class="pun" style="color: rgb(102, 102, 0);">);</span><span class="pln" style="color: rgb(0, 0, 0);">   </span><span class="com" style="color: rgb(136, 0, 0);">// These variables hold the previous two elements of the vector.</span><span class="pln" style="color: rgb(0, 0, 0);">   </span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln" style="color: rgb(0, 0, 0);"> x </span><span class="pun" style="color: rgb(102, 102, 0);">=</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="lit" style="color: rgb(0, 102, 102);">1</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln" style="color: rgb(0, 0, 0);">   </span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln" style="color: rgb(0, 0, 0);"> y </span><span class="pun" style="color: rgb(102, 102, 0);">=</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="lit" style="color: rgb(0, 102, 102);">1</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln" style="color: rgb(0, 0, 0);">   </span><span class="com" style="color: rgb(136, 0, 0);">// Assign each element in the vector to the sum of the </span><span class="pln" style="color: rgb(0, 0, 0);">   </span><span class="com" style="color: rgb(136, 0, 0);">// previous two elements.</span><span class="pln" style="color: rgb(0, 0, 0);">   generate_n</span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="pln" style="color: rgb(0, 0, 0);">v</span><span class="pun" style="color: rgb(102, 102, 0);">.</span><span class="kwd" style="color: rgb(0, 0, 136);">begin</span><span class="pun" style="color: rgb(102, 102, 0);">()</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">+</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="lit" style="color: rgb(0, 102, 102);">2</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln" style="color: rgb(0, 0, 0);"> elementCount </span><span class="pun" style="color: rgb(102, 102, 0);">-</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="lit" style="color: rgb(0, 102, 102);">2</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">[=]()</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="kwd" style="color: rgb(0, 0, 136);">mutable</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="kwd" style="color: rgb(0, 0, 136);">throw</span><span class="pun" style="color: rgb(102, 102, 0);">()</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">-></span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">{</span><span class="pln" style="color: rgb(0, 0, 0);">            </span><span class="com" style="color: rgb(136, 0, 0);">// Generate current value.</span><span class="pln" style="color: rgb(0, 0, 0);">      </span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln" style="color: rgb(0, 0, 0);"> n </span><span class="pun" style="color: rgb(102, 102, 0);">=</span><span class="pln" style="color: rgb(0, 0, 0);"> x </span><span class="pun" style="color: rgb(102, 102, 0);">+</span><span class="pln" style="color: rgb(0, 0, 0);"> y</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln" style="color: rgb(0, 0, 0);">      </span><span class="com" style="color: rgb(136, 0, 0);">// Update previous two values.</span><span class="pln" style="color: rgb(0, 0, 0);">      x </span><span class="pun" style="color: rgb(102, 102, 0);">=</span><span class="pln" style="color: rgb(0, 0, 0);"> y</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln" style="color: rgb(0, 0, 0);">      y </span><span class="pun" style="color: rgb(102, 102, 0);">=</span><span class="pln" style="color: rgb(0, 0, 0);"> n</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln" style="color: rgb(0, 0, 0);">      </span><span class="kwd" style="color: rgb(0, 0, 136);">return</span><span class="pln" style="color: rgb(0, 0, 0);"> n</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln" style="color: rgb(0, 0, 0);">   </span><span class="pun" style="color: rgb(102, 102, 0);">});</span><span class="pln" style="color: rgb(0, 0, 0);">   </span><span class="com" style="color: rgb(136, 0, 0);">// Print the contents of the vector.</span><span class="pln" style="color: rgb(0, 0, 0);">   for_each</span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="pln" style="color: rgb(0, 0, 0);">v</span><span class="pun" style="color: rgb(102, 102, 0);">.</span><span class="kwd" style="color: rgb(0, 0, 136);">begin</span><span class="pun" style="color: rgb(102, 102, 0);">(),</span><span class="pln" style="color: rgb(0, 0, 0);"> v</span><span class="pun" style="color: rgb(102, 102, 0);">.</span><span class="kwd" style="color: rgb(0, 0, 136);">end</span><span class="pun" style="color: rgb(102, 102, 0);">(),</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">[](</span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln" style="color: rgb(0, 0, 0);"> n</span><span class="pun" style="color: rgb(102, 102, 0);">)</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">{</span><span class="pln" style="color: rgb(0, 0, 0);"> cout </span><span class="pun" style="color: rgb(102, 102, 0);"><<</span><span class="pln" style="color: rgb(0, 0, 0);"> n </span><span class="pun" style="color: rgb(102, 102, 0);"><<</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="str" style="color: rgb(0, 136, 0);">" "</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">});</span><span class="pln" style="color: rgb(0, 0, 0);">   cout </span><span class="pun" style="color: rgb(102, 102, 0);"><<</span><span class="pln" style="color: rgb(0, 0, 0);"> endl</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln" style="color: rgb(0, 0, 0);">   </span><span class="com" style="color: rgb(136, 0, 0);">// Print the local variables x and y.</span><span class="pln" style="color: rgb(0, 0, 0);">   </span><span class="com" style="color: rgb(136, 0, 0);">// The values of x and y hold their initial values because </span><span class="pln" style="color: rgb(0, 0, 0);">   </span><span class="com" style="color: rgb(136, 0, 0);">// they are captured by value.</span><span class="pln" style="color: rgb(0, 0, 0);">   cout </span><span class="pun" style="color: rgb(102, 102, 0);"><<</span><span class="pln" style="color: rgb(0, 0, 0);"> x </span><span class="pun" style="color: rgb(102, 102, 0);"><<</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="str" style="color: rgb(0, 136, 0);">" "</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);"><<</span><span class="pln" style="color: rgb(0, 0, 0);"> y </span><span class="pun" style="color: rgb(102, 102, 0);"><<</span><span class="pln" style="color: rgb(0, 0, 0);"> endl</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln" style="color: rgb(0, 0, 0);"></span><span class="pun" style="color: rgb(102, 102, 0);">}</span><span class="pln" style="color: rgb(0, 0, 0);"></span>

<span class="com" style="color: rgb(136, 0, 0);">#include</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="str" style="color: rgb(0, 136, 0);"><functional></span><span class="pln" style="color: rgb(0, 0, 0);"></span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln" style="color: rgb(0, 0, 0);"> main</span><span class="pun" style="color: rgb(102, 102, 0);">()</span><span class="pln" style="color: rgb(0, 0, 0);"></span><span class="pun" style="color: rgb(102, 102, 0);">{</span><span class="pln" style="color: rgb(0, 0, 0);">   </span><span class="com" style="color: rgb(136, 0, 0);">// Assign the lambda expression that adds two numbers to an auto variable.</span><span class="pln" style="color: rgb(0, 0, 0);">   </span><span class="kwd" style="color: rgb(0, 0, 136);">auto</span><span class="pln" style="color: rgb(0, 0, 0);"> f1 </span><span class="pun" style="color: rgb(102, 102, 0);">=</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">[]</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln" style="color: rgb(0, 0, 0);"> x</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln" style="color: rgb(0, 0, 0);"> y</span><span class="pun" style="color: rgb(102, 102, 0);">)</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">{</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="kwd" style="color: rgb(0, 0, 136);">return</span><span class="pln" style="color: rgb(0, 0, 0);"> x </span><span class="pun" style="color: rgb(102, 102, 0);">+</span><span class="pln" style="color: rgb(0, 0, 0);"> y</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">};</span><span class="pln" style="color: rgb(0, 0, 0);">    </span><span class="com" style="color: rgb(136, 0, 0);">// Assign the same lambda expression to a function object.</span><span class="pln" style="color: rgb(0, 0, 0);">   </span><span class="kwd" style="color: rgb(0, 0, 136);">using</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="kwd" style="color: rgb(0, 0, 136);">namespace</span><span class="pln" style="color: rgb(0, 0, 0);"> std</span><span class="pun" style="color: rgb(102, 102, 0);">::</span><span class="pln" style="color: rgb(0, 0, 0);">tr1</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln" style="color: rgb(0, 0, 0);">   </span><span class="kwd" style="color: rgb(0, 0, 136);">function</span><span class="pun" style="color: rgb(102, 102, 0);"><</span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pun" style="color: rgb(102, 102, 0);">)></span><span class="pln" style="color: rgb(0, 0, 0);"> f2 </span><span class="pun" style="color: rgb(102, 102, 0);">=</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">[]</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">(</span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln" style="color: rgb(0, 0, 0);"> x</span><span class="pun" style="color: rgb(102, 102, 0);">,</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="kwd" style="color: rgb(0, 0, 136);">int</span><span class="pln" style="color: rgb(0, 0, 0);"> y</span><span class="pun" style="color: rgb(102, 102, 0);">)</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">{</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="kwd" style="color: rgb(0, 0, 136);">return</span><span class="pln" style="color: rgb(0, 0, 0);"> x </span><span class="pun" style="color: rgb(102, 102, 0);">+</span><span class="pln" style="color: rgb(0, 0, 0);"> y</span><span class="pun" style="color: rgb(102, 102, 0);">;</span><span class="pln" style="color: rgb(0, 0, 0);"> </span><span class="pun" style="color: rgb(102, 102, 0);">};</span><span class="pln" style="color: rgb(0, 0, 0);"></span><span class="pun" style="color: rgb(102, 102, 0);">}</span><span class="pln" style="color: rgb(0, 0, 0);"></span>

更多例子请参阅 Examples of Lambda Expressions，本文的数个例子也多来源于此。

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