ifstream in(ifile);     //构造一个ifstream并打开给定文件
ofstream out;           //输出文件流未关联到任何文件

用fstream代替iostream&

#ifndef SALES_DATA_H_INCLUDED
#define SALES_DATA_H_INCLUDED

#include <string>
#include <iostream>

class Sales_data
{
    friend Sales_data add(const Sales_data&, const Sales_data&);
    friend std::ostream &print(std::ostream&, const Sales_data&);
    friend std::istream &read(std::istream&, Sales_data&);
public:
	// constructors
	Sales_data(): units_sold(0), revenue(0.0) { }
	Sales_data(const std::string &s):
	           bookNo(s), units_sold(0), revenue(0.0) { }
	Sales_data(const std::string &s, unsigned n, double p):
	           bookNo(s), units_sold(n), revenue(p*n) { }
	Sales_data(std::istream &);

	// operations on Sales_data objects
	std::string isbn() const { return bookNo; }
	Sales_data& combine(const Sales_data&);
	double avg_price() const;
private:
	std::string bookNo;
	unsigned units_sold;
	double revenue;
};


#endif // SALES_DATA_H_INCLUDED

#include <iostream>
using std::istream; using std::ostream;

#include "Sales_data.h"
Sales_data::Sales_data(std::istream &is)
{
	// read will read a transaction from is into this object
	read(is, *this);
}

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

// add the value of the given Sales_data into this object
Sales_data&
Sales_data::combine(const Sales_data &rhs)
{
	units_sold += rhs.units_sold; // add the members of rhs into
	revenue += rhs.revenue;       // the members of ``this'' object
	return *this; // return the object on which the function was called
}

Sales_data
add(const Sales_data &lhs, const Sales_data &rhs)
{
	Sales_data sum = lhs;  // copy data members from lhs into sum
	sum.combine(rhs);      // add data members from rhs into sum
	return sum;
}

// transactions contain ISBN, number of copies sold, and sales price
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;
}

/*
* 功能:用fstream代替iostream&
* 时间:2014年6月7日07:58:39
* 作者:cutter_point
*/

#include"Sales_data.h"
#include"Sales_data.cc"
#include<fstream>

using namespace std;

int main()
{
    string argv[3];
    ifstream input(argv[1]);    //打开销售记录文件
    ofstream output(argv[2]);   //打开输出文件
    Sales_data total;           //保存销售总额的变量

    if(read(input, total))      //读取一条记录
    {
       //保存下一条销售记录的变量
       Sales_data trans;
       while(read(input, trans))
       {
            //读取剩余的记录
            if(total.isbn() == trans.isbn())
                total.combine(trans);   //更新销售总额
            else
            {
                print(output, total)<<endl;     //打印结果
                total=trans;        //处理下一本书
            }
        }

        print(output, total)<<endl;     //打印最后一本书
    }
    else
        cerr<<"No data?!"<<endl;

    return 0;
}

/*
* 功能:读取文件
* 时间:2014年6月7日08:51:44
* 作者:cutter_point
*/

#include<iostream>
#include<fstream>
#include<string>
#include<vector>

using namespace std;

int main()
{
    vector<string> v1;
    ifstream infile("C:\\booklist.txt");
    char s1[30];

    while(infile)
    {
        infile.getline(s1,30);
        v1.push_back(s1);
    }

    infile.close();

    for(int i=0 ; i<v1.size() ; ++i)
    {
        cout<<v1[i]<<endl;
    }

    return 0;
}

文件模式

/*
* 功能:文件模式
* 时间:2014年6月7日09:06:29
* 作者:cutter_point
*/

#include<iostream>
#include<string>
#include<fstream>
#include<vector>

using namespace std;

int main()
{
    ofstream outfile;
    outfile.open("booklist.txt", ofstream::app);
    int i=0;

    while(i != 2)
    {
        outfile<<"This is just a kinding!!"<<endl;
        ++i;
    }

    outfile.close();


    return 0;
}