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";
}();
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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);
} |
- [] 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();
} |
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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/