C++ ifstream问题

逐梦草根 2017-12-08 07:10:18

一个C++程序，main函数中用ifstream打不开txt文件，我将sales_data.txt文件存放在跟源码一样的目录下

#include <iostream>
#include <string>
#include <fstream>
#include <sstream>
using namespace std;

class Sales_data{
public:
friend istream &read(istream &, Sales_data &);//一个友元函数read,便于Sales_data类直接访问
friend ostream &print(ostream &os, const Sales_data &item);
Sales_data() = default;//默认构造函数
Sales_data(const std::string &s) : bookNo(s){ }
Sales_data(const std::string &s, unsigned n, double p) : bookNo(s), units_sold(n), revenue(p*n){ }
Sales_data(std::istream &is){
read(is, *this);
}

string isbn() const { return bookNo; }
Sales_data& combine(const Sales_data&);
double avg_price() const;

private:
string bookNo;
unsigned units_sold = 0;
double revenue = 0.0;
};

Sales_data add(const Sales_data&, const Sales_data&);
std::ostream &print(std::ostream&, const Sales_data&);
std::istream &read(std::istream&, Sales_data&);

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

Sales_data& Sales_data::combine(const Sales_data &rhs)
{
units_sold += rhs.units_sold;
revenue += rhs.revenue;
return *this;
}

istream &read(istream &is, Sales_data &item)
{
double price = 0;
is >> item.bookNo >> item.units_sold >> price;
item.revenue = price * item.units_sold;
return is;
}

ostream &print(ostream &os, const Sales_data &item){
os << item.isbn() << " " << item.units_sold << " "
<< item.revenue << " " << item.avg_price();
return os;
}

Sales_data add(const Sales_data &lhs, const Sales_data &rhs){
Sales_data sum = lhs;
sum.combine(rhs);
return sum;
}

/*
Sales_data::Sales_data(std::istream &is)
{
read(is,*this);
}
*/

int main()
{
ifstream in("sales_data.txt");//为什么在这里打不开txt文件啊
//改动地方，新增一个Sales_data.txt
Sales_data total;
if (read(in, total))
{
//read(cin,total); 变为read(in,total);
Sales_data trans;
while (read(in, trans))
{
//read(cin, total); 变为read(in,total);
if (total.isbn() == trans.isbn())
total.combine(trans);
else
{
print(cout, total) << endl;
total = trans;
}
}
print(cout, total) << endl;
}
else{
cerr << "No data?!" << endl;
}
}

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