c++ - C++primer 5ed 1.23 和 1.4.4 中的示例有不同的输出

Question

这是 1.4.4 中的代码

#include<iostream>
int main()
{
    int currval=0,val=0;
    if(std::cin>>currval){
        int cnt=1;
        while(std::cin>>val){
            if(val==currval){
                ++cnt;
            }   
            else{
            std::cout<<currval<<" occurs "
            <<cnt<<" times "<<std::endl;
            currval = val;
            cnt=1;
            }
        }
        std::cout<<currval<<" occurs "
        <<cnt<<" times "<<std::endl;
    }
    return 0; 
}

这是实践中的代码 1.23

#include<iostream>
#include"Sales_item.hpp"
int main()
{
    Sales_item curbok;
    Sales_item bok;
    if(std::cin>>curbok)
    {
        int cnt=1;
        while(std::cin>>bok)
        {
            if (bok.isbn() == curbok.isbn())
            {
                ++cnt;
            }
            else
            {
                std::cout<<"Total selling of "
                <<curbok.isbn()<<" is "<<cnt
                <<std::endl; 
                curbok = bok; 
                cnt = 1;              
            }
        }
        std::cout<<"Total selling of"
        <<curbok.isbn()<<" is "<<cnt<<std::endl; 
        std::cout<<"222"<<std::endl;
    }
    return 0;
}

我认为他们有类似的过程来实现功能。但在第一个代码中：

1. 型号 1 1 1 2 2 2

2. 键入 Ctrl+Z

3. 输出答案

   1 occurs 3 times 
   2 occurs 3 times
   

在第二个代码中

1. 类型 202-x 2 2、202-x 2 2、203 - x 2 2
2. 键入 Ctrl+Z 并按 Enter
3. 输出答案

Total selling of 202-x is 2

4. 再次键入 Ctrl+z 并按 Enter
5. 输出剩下的答案

Total selling of 203-x is 1

为什么第二个代码需要按两次 Ctrl+Z 才能结束流

我在Windows10系统中运行VScode和MinGW-x64 g++中的代码

1.23 代码中包含的 Sales_item.hpp：

#ifndef SALESITEM_H
// we're here only if SALESITEM_H has not yet been defined 
#define SALESITEM_H

#include "Version_test.hpp" 

// Definition of Sales_item class and related functions goes here
#include <iostream>
#include <string>

class Sales_item {
// these declarations are explained section 7.2.1, p. 270 
// and in chapter 14, pages 557, 558, 561
friend std::istream& operator>>(std::istream&, Sales_item&);
friend std::ostream& operator<<(std::ostream&, const Sales_item&);
friend bool operator<(const Sales_item&, const Sales_item&);
friend bool 
operator==(const Sales_item&, const Sales_item&);
public:
    // constructors are explained in section 7.1.4, pages 262 - 265
    // default constructor needed to initialize members of built-in type
#if defined(IN_CLASS_INITS) && defined(DEFAULT_FCNS)
    Sales_item() = default;
#else
    Sales_item(): units_sold(0), revenue(0.0) { }
#endif
    Sales_item(const std::string &book):
              bookNo(book), units_sold(0), revenue(0.0) { }
    Sales_item(std::istream &is) { is >> *this; }
public:
    // operations on Sales_item objects
    // member binary operator: left-hand operand bound to implicit this pointer
    Sales_item& operator+=(const Sales_item&);
    
    // operations on Sales_item objects
    std::string isbn() const { return bookNo; }
    double avg_price() const;
// private members as before
private:
    std::string bookNo;      // implicitly initialized to the empty string
#ifdef IN_CLASS_INITS
    unsigned units_sold = 0; // explicitly initialized
    double revenue = 0.0;
#else
    unsigned units_sold;  
    double revenue;       
#endif
};

// used in chapter 10
inline
bool compareIsbn(const Sales_item &lhs, const Sales_item &rhs) 
{ return lhs.isbn() == rhs.isbn(); }

// nonmember binary operator: must declare a parameter for each operand
Sales_item operator+(const Sales_item&, const Sales_item&);

inline bool 
operator==(const Sales_item &lhs, const Sales_item &rhs)
{
    // must be made a friend of Sales_item
    return lhs.units_sold == rhs.units_sold &&
           lhs.revenue == rhs.revenue &&
           lhs.isbn() == rhs.isbn();
}

inline bool 
operator!=(const Sales_item &lhs, const Sales_item &rhs)
{
    return !(lhs == rhs); // != defined in terms of operator==
}

// assumes that both objects refer to the same ISBN
Sales_item& Sales_item::operator+=(const Sales_item& rhs) 
{
    units_sold += rhs.units_sold; 
    revenue += rhs.revenue; 
    return *this;
}

// assumes that both objects refer to the same ISBN
Sales_item 
operator+(const Sales_item& lhs, const Sales_item& rhs) 
{
    Sales_item ret(lhs);  // copy (|lhs|) into a local object that we'll return
    ret += rhs;           // add in the contents of (|rhs|) 
    return ret;           // return (|ret|) by value
}

std::istream& 
operator>>(std::istream& in, Sales_item& s)
{
    double price;
    in >> s.bookNo >> s.units_sold >> price;
    // check that the inputs succeeded
    if (in)
        s.revenue = s.units_sold * price;
    else 
        s = Sales_item();  // input failed: reset object to default state
    return in;
}

std::ostream& 
operator<<(std::ostream& out, const Sales_item& s)
{
    out << s.isbn() << " " << s.units_sold << " "
        << s.revenue << " " << s.avg_price();
    return out;
}

double Sales_item::avg_price() const
{
    if (units_sold) 
        return revenue/units_sold; 
    else 
        return 0;
}
#endif

标签： c++visual-studio-codeg++