C++ - 重载I/O操作符的注意 - c++编程基础

1. 输出操作符(ostream)重载

函数: std::ostream &operator<< (std::ostream& os, const ClassA& ca);

ostream需要修改, 不能复制, 所以应该为非常量引用类型(nonconst &); 输出类不需要修改, 应该为常量引用类型(const &);

函数有可能使用内部的私有成员, 需要定义为友元(friend);

重载操作符应该为非类成员函数(nonmember function). 如果为类成员函数, 则也必须为标准库成员函数, 显然无法完成.

注意函数不要有格式信息(minimal formatting), 为了和标准输入操作符进行统一.

2. 输入操作符(istream)重载

函数: std::istream &operator>> (std::istream& is, ClassA& ca);

基本同输出操作符;

参数都为nonconst, 都需要修改;

操作符函数应该包括错误恢复(error recovery),保证输入错误时, 不会产生未知错误;

可以增加I/O条件状态(condition state)进行判断, 输入错误原因.

代码如下, 包含以上所有特性, 注意注释:

/* 
 * cppprimer.cpp 
 * 
 *  Created on: 2013.11.7 
 *      Author: Caroline 
 */  
  
#include   
#include   
#include   
  
class HighHeel {  
friend std::ostream &operator<< (std::ostream& os, const HighHeel& hh);  
friend std::istream &operator>> (std::istream& is, HighHeel& hh);  
friend HighHeel operator+ (const HighHeel& lhs, const HighHeel& rhs);  
public:  
    int heel() const{  
        return (wedgeHeel + kittenHeel + stilettoHeel);  
    }  
    int boot() const{  
        return (kinkyBoot + thighHighBoot);  
    }  
private:  
    int wedgeHeel = 2; //坡跟鞋  
    int kittenHeel = 2; //中跟鞋  
    int stilettoHeel = 2; //细跟鞋  
    int kinkyBoot = 5; //长筒女靴  
    int thighHighBoot = 5; //过膝长靴  
};  
  
std::ostream &operator<< (std::ostream& os, const HighHeel& hh)  
{  
    os << "Heels: " << hh.heel() << " "  
        << "Boots: " << hh.boot();  
    return os;  
}  
std::istream &operator>




> (std::istream& is, HighHeel& hh)  
{  
    is >> hh.wedgeHeel >> hh.kittenHeel >> hh.stilettoHeel  
        >> hh.kinkyBoot >> hh.thighHighBoot;  
    if ( (is.rdstate() & is.failbit) != 0) //检查错误位  
        std::cerr << "Error to input!" << std::endl;  
    if (!is)  
        hh = HighHeel();  
    return is;  
}  
  
HighHeel operator+ (const HighHeel& lhs, const HighHeel& rhs)  
{  
    HighHeel sum = lhs;  
    sum.wedgeHeel += rhs.wedgeHeel;  
    sum.kittenHeel += rhs.kittenHeel;  
    sum.stilettoHeel += rhs.stilettoHeel;  
    sum.kinkyBoot += rhs.kinkyBoot;  
    sum.thighHighBoot += rhs.thighHighBoot;  
    return sum;  
}  
  
int main (void) {  
    HighHeel hh;  
    std::cout << hh << std::endl;  
    std::cout << "Please input heels quantity (5 numbers) :" << std::endl;  
    std::cin >> hh;  
    std::cout << hh << std::endl;  
    HighHeel hh2;  
    std::cout << hh + hh2 << std::endl;  
    return 0;  
}

C++ - 重载I/O操作符 的 注意

C++ - 重载I/O操作符的注意