創建一個匿名函數並執行。Objective-C采用的是上尖號^，而C++ 11采用的是配對的方括號[]。實例如下：
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#include <iostream>
using
namespace
std;
int
main()
{
[]{
cout <<
"Hello,Worldn"
;
}();
}
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我們也可以方便的將這個創建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);
}
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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();
}
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vs 報錯
error C3493: 無法隱式捕獲“i”，因為尚未指定默認捕獲模式
error C2064: 項不會計算為接受 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需要在 [] 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 = [=]{
// [=] 表明將外部的所有變量拷貝一份到該函數內部
cout << i;
};
func();
}
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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();
}
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[&] 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();
}
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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]{
// 默認拷貝外部所有變量，但引用變量 i
cout <<
"i:"
<< &i << endl;
cout <<
"j:"
<< &j << endl;
};
fun1();
}
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1
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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();
}
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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();
}
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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();
}
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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();
// 這里 this 調用的就是 class test 的對象了
};
fun();
}
};
int
main()
{
test t;
t.lambda();
}
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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/