问题描述
//在C++ Primer中文版230页Sales_data类中，有个问题不太明白。当接口函数只有 combine的时候，编译成功，一旦加入 read 和 print两个非成员接口函数，则编译报错，请指教
ifndef SALES_DATA_H_INCLUDEDdefine SALES_DATA_H_INCLUDEDinclude <iostream>include<string>struct Sales_data{
std::string isbn()const {return bookNo;}Sales_data& combine(const Sales_data &rhs);std::string bookNo;unsigned uints_sold =0;double revenue = 0.0;
}; Sales_data& Sales_data::combine(const Sales_data &rhs)
{uints_sold += rhs.uints_sold;revenue += rhs.revenue;return *this;
}std::istream &read (istream &is , Sales_data &item){
double price = 0;is >> item.bookNo >> item.uints_sold >> price;item.revenue = price * item.uints_sold ;return is;
}std::ostream &print(ostream &os, const Sales_data &item){
os << item.isbn() << ' ' << item.uints_sold << ' ' << item.revenue << ' ';return os;
}
endif // SALES_DATA_H_INCLUDED
问题解答
回答1：请在 #include <string>后面加上一句using namespace std;
贴代码的时候不要直接贴，使用添加代码的功能。
#ifndef SALES_DATA_H_INCLUDED#define SALES_DATA_H_INCLUDED#include <iostream>#include <string>using namespace std;struct Sales_data { std::string isbn() const {return(bookNo); } Sales_data & combine( const Sales_data &rhs ); std::string bookNo; unsigned uints_sold = 0; doublerevenue= 0.0;};Sales_data & Sales_data::combine( const Sales_data &rhs ){ uints_sold += rhs.uints_sold; revenue+= rhs.revenue; return(*this);}std::istream &read(istream &is, Sales_data &item ){ double price = 0; is >> item.bookNo >> item.uints_sold >> price; item.revenue = price * item.uints_sold; return(is);}std::ostream &print( ostream &os, const Sales_data &item ){ os << item.isbn() << ' ' << item.uints_sold << ' ' << item.revenue << ' '; return(os);}#endif /* SALES_DATA_H_INCLUDED */
