c++中的类型推导

#include <iostream>
using namespace std;
int main(){
    {
        const int &i = 10;
        auto j = i;   //类型推导时会丢失引用、const语义
        auto &k = i;  //保留引用或 cv 语义
        j = 11;  //可修改
        cout << " j = " << j << endl; 
        k = 12;  //error: assignment of read-only reference 'k'
    //万能引用，根据初始值属性来判断是左值引用还是右值引用
    auto&& m = i;  //左值引用
    auto&& n = 10;  //右值引用
    }    
    return 0;
} 

#include <iostream>
using namespace std;
int main(){
    {
        int a = 1;
        float b = 2.0;
        decltype(a+b) c = a + b;
        cout << "a+b= " << c << typeid(c).name() << endl;  //a+b= 3f
        auto f = [](int a, double b) {  //匿名函数
            return a + b;
        };
        decltype (f(a, b)) d = b;  //会将a的int类型与b的float类型都转换为double类型
        cout << "d= " << d << typeid(d).name() << endl;  //d= 2d
        decltype (a+=b) e = a;  //左值引用
        e = 19;
        cout << "a= " << a <<typeid(a).name() << endl;  //a= 19, e的值修改, a的值得修改了
    }
    return 0;
}