引用（五）

///看了个引用的小程， 发现我需要复习了。。。。。。#include<iostream>using namespace std;#include<string>struct free_throws{    std::string name;    int made;    int attempts;    float percent;};void display(const free_throws & ft);void set_pc(free_throws & ft);free_throws & accumulate(free_throws & target, const free_throws & source);int main(){    free_throws one = {"aaa", 13, 14};    free_throws two = {"bbb", 10, 16};    free_throws three = {"ccc", 7, 9};    free_throws four = {"ddd", 5, 9};    free_throws five = {"eee", 6, 14};    free_throws team = {"fff", 0, 0};    free_throws dup;    set_pc(one);    display(one);    accumulate(team, one);    display(team);    display(accumulate(team, two));    accumulate(accumulate(team, three), four);    display(team);    dup = accumulate(team, five);    std::cout << "Displaying team:\n";    display(team);    std::cout << "Displaying dup after assignment:\n";    display(dup);    set_pc(four);    accumulate(dup, five) = four;    std::cout << "Displaying dup after ill-advised assignment:\n";    display (dup);    return 0;}void display(const free_throws & ft){    using std::cout;    cout << "Name: " << ft.name <<endl;    cout << " Made: " << ft.made <<"\t";    cout << " Attempts: " << ft.attempts << "\t";    cout << " Precents: " << ft.percent << "\n";}void set_pc(free_throws & ft){    if(ft.attempts != 0)        ft.percent = 100.0f * float(ft.made)/float(ft.attempts);    else        ft.percent = 0;}free_throws & accumulate(free_throws & target, const free_throws & source){    target.attempts += source.attempts;    target.made += source.made;    set_pc(target);    return target;}/*Name: aaa Made: 13        Attempts: 14    Precents: 92.8571Name: fff Made: 13        Attempts: 14    Precents: 92.8571Name: fff Made: 23        Attempts: 30    Precents: 76.6667Name: fff Made: 35        Attempts: 48    Precents: 72.9167Displaying team:Name: fff Made: 41        Attempts: 62    Precents: 66.129Displaying dup after assignment:Name: fff Made: 41        Attempts: 62    Precents: 66.129Displaying dup after ill-advised assignment:Name: ddd Made: 5         Attempts: 9     Precents: 55.5556Process returned 0 (0x0)   execution time : 0.689 sPress any key to continue.*////下面对以前对引用的总结做一些补充，前面我们已经讲到了左值引用，///而C++11新增了另一种引用///右值引用。 这种引用可指向右值。用&&声明。double && rref = std::sqrt(36.00); /// not allowed for double &double j = 15.0;double && jref = 2.0*j + 18.5;/// not allowed for double &std::cout << rref << endl;///display 6.0std::cout << jref << endl;///display 48.5

常规（非引用）返回类型是右值，即不能通过地址访问的值。其他右值包括字面值（如10.0）和表达式（如x+y）。常规函数表达式返回值为右值，是因为这种返回值位于临时内存单元中。运行到下一条语句时， 他们可能不再存在。