C++11_ Lambda

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这次主要介绍C++11的Lambda语法,一个非常给力的语法

1.组成 : [...导入符号](...参数)mutable(可改写)  throwSpec(抛出异常) ->retType(返回值){...}

---

2.最简单的Lamdba

#include <iostream>

int main(int argc, const char * argv[]) {

    [] {
        std::cout<< "hello lambda" <<std::endl;
    } ();

    return 0;
}

 输出结果

 

---

3.重新定义

#include <iostream>

int main()
{
    auto l =[] {
        std::cout<< "hello lambda111" <<std::endl;
    } ;

    l();//调用
    return 0;
}

 输出结果 

 

---

 4.获取外部变量

int main()
{
    
    //by value
    int id = 0;
    auto f = [id]() mutable{
        std::cout<<"id = "<<id<<std::endl;
        ++id; 
    };
    id = 42;
    f();
    f();
    f();
    return 0;
}

 输出结果

可能会很诧异为啥是输出结果为啥是0,1,2,因为传入的外界变量方式是by value,所以外界的id改变 不会改变lambda内的 id

引用传参

#include <iostream>

int main()
{
    //by reference
    int id = 0;
    auto g = [&id]() mutable{
        std::cout<<"id = "<<id<<std::endl;
        id++;
    };
    id = 10;
    g();
    g();
    g();
    return 0;
}

 输出结果

---

5.带参数

#include <iostream>

int main()
{
    //by reference
    int id = 0;
    auto g = [&id](int parm) mutable{
        std::cout<<"id = "<<id<<std::endl;
        std::cout<<"parm = "<<parm<<std::endl;
        id++;
    };
    id = 10;
    g(7);
    g(8);
    g(9);
    return 0;
}

输出结果

---

6.有返回值 

#include <iostream>

int main()
{
    //by reference
    int id = 0;
    auto g = [&id](int parm) mutable{
        std::cout<<"id = "<<id<<std::endl;
        std::cout<<"parm = "<<parm<<std::endl;
        return parm+id;
    };
    id = 10;
    int tmp = g(9);
    std::cout<< "tmp = " << tmp << std::endl;
    return 0;
}

 输出结果

---

 7.使代码简化

    vector<int> vi{1,2,3,4,5,6,7,8,9,10};
    int x = 2;
    int y = 9;
    vi.erase(remove_if(vi.begin(), vi.end(), [x,y](int n){return x<=n && n<=y;}),vi.end());
    for(auto i:vi)
    cout<<i<<endl;

上面这段代码与下面代码意义相同

class ABC_Test_14
{
public:
    ABC_Test_14(int a ,int b) :m_a(a),m_b(b){}
    bool operator()(int n) const
    {
        return m_a < n && n < m_b;
    }
    
private:
    int m_a;
    int m_b;
};
...
vi.erase(remove_if(vi.begin(), vi.end(), ABC_Test_14(x,y)),vi.end());

 如有错误请指正.

 参照<<侯捷 C++新标准 C++11>>