求大神，帮忙分析下程序问题的原因 - C++教室 - C++论坛

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求大神，帮忙分析下程序问题的原因

程序代码：

#include <iostream>
#include <string>
#include <vector>
#include <cctype>
#include <stdexcept>
using namespace std;
using std::string;
using std::vector;

struct Sales_data {
    Sales_data& combine(const Sales_data&);
    string isbn() const { return bookNo; }
    double avg_price() const; 
     
    string bookNo;
    unsigned units_sold = 0;
    double revenue = 0.0;
}; 
Sales_data add(const Sales_data&, const Sales_data&);
ostream &print(ostream, const Sales_data&);
istream &read(istream, Sales_data&);

int main()
{
    Sales_data total;
    
    if(read(cin, total))
    {
        Sales_data trans;
        while(read(cin, trans)
        {
            if(total.isbn() == trans.isbn())
            {
                (trans);
            }
            else
            {
                print(cout, total) << endl;
                cout << '\n';
                total = trans;
            }
        }
        print(cout, total) << endl;
        
    }
    else
    {
        cerr << "No data?!" << endl;
        return -1;
    }
    return 0;
}

Sales_data& Sales_data::combine(const Sales_data &rhs)
{
    units_sold += rhs.units_sold;
    revenue += rhs.revenue;
    return *this;
}
double Sales_data::avg_price() const
{
    if(units_sold)
        return revenue/units_sold;
    else
        return 0;
}
Sales_data add(const Sales_data &lhs, const Sales_data &rhs)
{
    Sales_data sum = lhs;
    (rhs);
    return sum; 
}
ostream &print(ostream &os, const Sales_data &item)
{
    os << item.isbn() << " " << item.units_sold << " " << item.revenue << " " << item.avg_price() << endl;
    return os; 
}
istream &read(istream &is, Sales_data &item)
{
    double price = 0;
    is >> item.bookNo >> item.units_sold >> price;
    item.revenue = item.units_sold * price;
    return is;
}

这是问题程序的代码，无法通过编译。
编译器的错误提示是[Error] use of deleted function 'std::basic_istream<char>::basic_istream(const std::basic_istream<char>&)'
我觉得问题出在read函数上，于是我把read和print函数的定义放在main函数上面，竟然通过编译了。但是我不明白错误的原因，求大神指教。

搜索更多相关主题的帖子: std　const　return　read　item　

#include <iostream> #include <string> #include <vector> #include <cctype> #include <stdexcept> using namespace std; using std::string; using std::vector; struct Sales_data { Sales_data& combine(const Sales_data&); string isbn() const { return bookNo; } double avg_price() const; string bookNo; unsigned units_sold = 0; double revenue = 0.0; }; Sales_data add(const Sales_data&, const Sales_data&); ostream &print(ostream &os, const Sales_data &item) { os << item.isbn() << " " << item.units_sold << " " << item.revenue << " " << item.avg_price() << endl; return os; } istream &read(istream &is, Sales_data &item) { double price = 0; is >> item.bookNo >> item.units_sold >> price; item.revenue = item.units_sold * price; return is; } int main() { Sales_data total; if(read(cin, total)) Sales_data trans; while(read(cin, trans)) if(total.isbn() == trans.isbn()) { (trans); else { print(cout, total) << endl; cout << '\n'; total = trans; } } print(cout, total) << endl; } else { cerr << "No data?!" << endl; return -1; } return 0; } Sales_data& Sales_data::combine(const Sales_data &rhs) { units_sold += rhs.units_sold; revenue += rhs.revenue; return *this; } double Sales_data::avg_price() const { if(units_sold) return revenue/units_sold; else return 0; } Sales_data add(const Sales_data &lhs, const Sales_data &rhs) Sales_data sum = lhs; (rhs); return sum; }