C++11 lambda(匿名函数)表达式详细介绍

auto f = [](int a) -> int {return a + 1;};
cout << f(3) << endl;  //输出4

auto f = [](int a) {return a + 1;};

auto f = []{return 1;};

class A 
{
public:
    int i_ = 0;
    
    void func(int x,int y)
    {
        auto x1 = []{return i_;};  // error,没有捕获外部变量
        auto x2 = [=]{return i_ + x + y;}; //ok，按值捕获所有外部变量
        auto x3 = [&]{return i_ + x + y;}; //ok，按引用捕获所有外部变量
        auto x4 = [this]{return i_;}; //ok，捕获this指针
        auto x5 = [this]{return i_ + x + y;}; //error,没有捕获x和y变量
        auto x6 = [this,x,y]{return i_ + x + y;}; //ok，捕获了this指针和x、y变量
        auto x7 = [this]{return i_++;}; //ok，捕获了this指针，修改成员变量的值
    }
};

int a = 0 , b = 0 ;
auto f1 = []{return a;}; // error,没有捕获外部变量
auto f2 = [&]{return a++;}; //ok，捕获所有外部变量，并对a变量自加
auto f3 = [=]{return a;}; //ok，捕获所有外部变量，并返回a
auto f4 = [=]{return a++;}; //error,a变量是以复制方式捕获的，不能修改
auto f5 = [a]{return a+b;}; //error,没有捕获b变量
auto f6 = [a,&b]{return a+ (b++);}; //ok，捕获a以及b的引用，对b进行自加
auto f7 = [=,&b]{return a+ (b++);}; //ok, 捕获所有外部变量和b的引用，对b进行自加

int a = 0;
auto f = [=]{return a;};
a += 1;
cout << f() << endl;

int a = 0;
auto f1 = [=]{return a++;};  //error,修改按值捕获的外部变量
auto f2 = [=]() mutable {return a++;}; //ok

std::function<int(int)> f1 = [](int a){return a;};
std::function<int(void)> f2 = std::bind([](int a){return a;},123);

using func_t = int(*)(int);
func_t f = [](int a){return a;};
f(123);

typedef void(*Ptr)(int*);
Ptr p = [](int *p){delete p;};  //ok
Ptr p1 = [&](int *p){delete p;}; //error

#include <vector>
#include <algorithm>
class Count
{
public:
    Count(int &val):num(val){}
    void operator()(int val){
        if(!(val & 1)){
            ++num;
        }
    }
private:
    int &num;
};

int main()
{
    std::vector<int> v = {1,2,3,4,5,6,7};
    int count = 0;
    for_each(v.begin(),v.end(),Count(count));
    std::cout << count << endl;
    return 0;
}

#include <vector>
#include <algorithm>

int main()
{
    std::vector<int> v = {1,2,3,4,5,6,7};
    int count = 0;
    for_each(v.begin(),v.end(),[&count](int val){
        if(!(val & 1)){
            ++count;
        }
    });

    std::cout << count << endl;
    return 0;
}