C++ Lambda表达式基本用法（言简意赅，很是清楚）

建立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[]。实例以下：

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

咱们也能够方便的将这个建立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: 没法隐式捕获“i”，由于还没有指定默认捕获模式
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须要在 [] 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 = [=]{  // [=] 代表将外部的全部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]{ // 默认拷贝外部全部变量，但引用变量 i          cout << "i:" << &i << endl;          cout << "j:" << &j << endl;      };      fun1(); }

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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/