C++ Lambda表達式基本用法（言簡意賅，很是清楚）

建立一個匿名函數並執行。Objective-C採用的是上尖號^，而C++ 11採用的是配對的方括號[]。實例以下：

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

咱們也能夠方便的將這個建立的匿名函數賦值出來調用：

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#include <iostream> using namespace std;   int main() {      int i = 1024;      auto func = []( int i) { // (int i) 是指傳入改匿名函數的參數          cout << i;      };      func(i); }

捕獲選項

• [] 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

[] 不捕獲任何變量

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

vs 報錯
error C3493: 沒法隱式捕獲「i」，由於還沒有指定默認捕獲模式
error C2064: 項不會計算爲接受 0 個參數的函數

g++ 報錯：
error: ‘i’ is not captured

要直接沿用外部的變量須要在 [] 中指名捕獲。

[=] 拷貝捕獲

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#include <iostream> using namespace std;   int main() {      int i = 1024;      auto func = [=]{  // [=] 代表將外部的全部變量拷貝一份到該函數內部          cout << i;      };      func(); }

結果：
1024

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

[&] 引用捕獲

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

結果:
0x28ff0c
0x28ff0c

[=, &] 拷貝與引用混合

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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]{ // 默認拷貝外部全部變量，但引用變量 i          cout << "i:" << &i << endl;          cout << "j:" << &j << endl;      };      fun1(); }

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

[bar] 指定引用或拷貝

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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 未捕獲      };      fun1(); }

結果：
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 未捕獲      };      fun1(); }

結果：
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 未捕獲      };      fun1(); }

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

[this] 捕獲 this 指針

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#include <iostream> using namespace std;   class test { public :      void hello() {          cout << "test hello!n" ;      };      void lambda() {          auto fun = [ this ]{ // 捕獲了 this 指針              this ->hello(); // 這裏 this 調用的就是 class test 的對象了          };          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/