C++ Lambda表达式基本用法（言简意赅，非常清楚）

创建一个匿名函数并执行。Objective-C采用的是上尖号^，而C++ 11采用的是配对的方括号[]。实例如下：

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#include <iostream> using namespace std;   int main() {     []{         cout << "Hello,Worldn";     }(); }

我们也可以方便的将这个创建的匿名函数赋值出来调用：

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#include <iostream> using namespace std;   int main() {     int i = 1024;     auto func = [](int i) { // (int i) 是指传入改匿名函数的参数         cout << i;     };     func(i); }

捕获选项

• [] Capture nothing (or, a scorched earth strategy?)
• [&] Capture any referenced variable by reference
• [=] Capture any referenced variable by making a copy
• [=, &foo] Capture any referenced variable by making a copy, but capture variable foo by reference
• [bar] Capture bar by making a copy; don’t copy anything else
• [this] Capture the this pointer of the enclosing class

[] 不捕获任何变量

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#include <iostream> using namespace std;   int main() {     int i = 1024;     auto func = [] { cout << i; };     func(); }

vs 报错
error C3493: 无法隐式捕获“i”，因为尚未指定默认捕获模式
error C2064: 项不会计算为接受 0 个参数的函数

g++ 报错：
error: ‘i’ is not captured

要直接沿用外部的变量需要在 [] 中指名捕获。

[=] 拷贝捕获

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#include <iostream> using namespace std;   int main() {     int i = 1024;     auto func = [=]{  // [=] 表明将外部的所有变量拷贝一份到该函数内部         cout << i;     };     func(); }

结果：
1024

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#include <iostream> using namespace std;   int main() {     int i = 1024;     auto fun1 = [=]{         // fun1 内存在 i         cout << i; // 1024         auto fun2 = []{ // 未指名捕获， i 不存在             cout << i;         };         fun2();     };     fun1(); }

[&] 引用捕获

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#include <iostream> using namespace std;   int main() {     int i = 1024;     cout << &i << endl;     auto fun1 = [&]{         cout << &i << endl;     };     fun1(); }

结果:
0x28ff0c
0x28ff0c

[=, &] 拷贝与引用混合

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#include <iostream> using namespace std;   int main() {     int i = 1024, j = 2048;       cout << "i:" << &i << endl;     cout << "j:" << &j << endl;       auto fun1 = [=, &i]{ // 默认拷贝外部所有变量，但引用变量 i         cout << "i:" << &i << endl;         cout << "j:" << &j << endl;     };     fun1(); }

1

结果
outside i:0x28ff0c
outside j:0x28ff08
inside i:0x28ff0c
inside j:0x28ff04

[bar] 指定引用或拷贝

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#include <iostream> using namespace std;   int main() {     int i = 1024, j = 2048;       cout << "outside i value:" << i << " addr:" << &i << endl;       auto fun1 = [i]{         cout << "inside  i value:" << i << " addr:" << &i << endl;         // cout << j << endl; // j 未捕获     };     fun1(); }

结果：
outside i value:1024 addr:0x28ff08
inside i value:1024 addr:0x28ff04

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#include <iostream> using namespace std;   int main() {     int i = 1024, j = 2048;       cout << "outside i value:" << i << " addr:" << &i << endl;       auto fun1 = [&i]{         cout << "inside  i value:" << i << " addr:" << &i << endl;         // cout << j << endl; // j 未捕获     };     fun1(); }

结果：
outside i value:1024 addr:0x28ff08
inside i value:1024 addr:0x28ff08

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#include <iostream> using namespace std;   int main() {     int i = 1024, j = 2048, k;       cout << "outside i:" << &i << endl;     cout << "outside j:" << &j << endl;       auto fun1 = [i, &j]{         cout << "inside  i:" << &i << endl;         cout << "inside  j:" << &j << endl;         // cout << k; // k 未捕获     };     fun1(); }

结果：
outside i:0x28ff0c
outside j:0x28ff08
inside i:0x28ff00
inside j:0x28ff08

[this] 捕获 this 指针

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#include <iostream> using namespace std;   class test { public:     void hello() {         cout << "test hello!n";     };     void lambda() {         auto fun = [this]{ // 捕获了 this 指针             this->hello(); // 这里 this 调用的就是 class test 的对象了         };         fun();     } };   int main() {     test t;     t.lambda(); }

 

 

https://lellansin.wordpress.com/2014/01/02/c-lambda%E8%A1%A8%E8%BE%BE%E5%BC%8F%E5%9F%BA%E6%9C%AC%E7%94%A8%E6%B3%95/