15.lambda表达式

Posted 2020-10-27 喵小喵~

 1 #include <iostream>
 2 #include <array>
 3 using namespace std;
 4 
 5 //解决函数怀孕现象
 6 //[](){}
 7 //[] =引用,只读 =mutable读原本改副本 &读写原本 //&a,b a可读写,b只能读
 8 //() 参数,int a,int b
 9 //{}语句
10 void main()
11 {
12     //lambda表达式
13     auto fun1 = [] {cout << "hello" << endl; cout << "hello2" << endl; };//函数指针
14     fun1();//括号起到调用的作用
15 
16     //[](参数列表){执行逻辑}
17     auto fun2 = [](char *str) {cout << str << endl; };
18     fun2("hello3");
19 
20     //lambda带参函数
21     auto fun3 = [](int a, int b) {return a + b; };
22     cout << fun3(10, 19) << endl;
23 
24     //->用在(){}之间,用于确定返回值类型
25     auto fun4 = [](int a, int b)->double {return a + b; };
26     cout << fun4(10, 19) << endl;
27 
28     //decltype解决类型自动推理
29     auto fun5 = [](int a, int b)->decltype(a+b) {return a + b; };
30     cout << fun5(10, 19) << endl;
31 
32     int num1 = 20;
33     int num2 = 33;
34     //=可以使用外部变量,只能读不能写
35     auto fun6 = [=](){cout << num1 << num2 << endl; };
36     fun6();
37 
38     //&可以使用外部变量,读写(对原数据的操作)
39     auto fun7 = [&](){num1 = 1; cout << num1 << num2 << endl; };
40     fun7();
41 
42     //mutable可以使用外部变量,读写(副本机制,不对原数据进行改变)
43     auto fun8 = [=]()mutable{num1 = 1; cout << num1 << num2 << endl; };
44     fun8();
45 
46     //指定可读写的元素 num1可读可写,num2只能读
47     auto fun9 = [&num1, num2]() {num1 = 30; cout << num2 << endl; };
48     fun9();
49 
50     //mutable可读可写但作用的是副本
51     auto fun10 = [num1, num2]() mutable{num1 = 30; cout << num2 << endl; };
52     fun10();
53 
54     //lambda与auto
55     auto fun11 = [](auto a, auto b)->decltype(a+b){return a + b; };
56     cout << fun11(1,3.9) << endl;
57 
58     //内嵌调用lambda
59     array<int, 10> myarray{1, 2, 3, 4, 5, 6, 7, 8, 9, 0};
60     for_each(myarray.begin(), myarray.end(), [](int &num) {num += 1; cout << num << endl; });
61     cin.get();
62 }