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C++ primer plus 文件处理程序

第一个程序：将内容写入txt文本

#include "stdafx.h"

#include <iostream>

#include <fstream> //for file I/O

using namespace std;

int main(int argc, char* argv[])

{

char automobile[50];

int year;

double a_price;

double d_price;

ofstream outFile; //creat object for output

/* associate with a file在这里，程序运行之前，文件carinfo.txt并不存在。

* 在这种情况下，方法open()将新建一个名为carinfo.txt的文件。运行该程序

* 之后，文件carinfo.txt将存在。默认情况下，open()将首先截短该文件，即

* 将其长度截短到零——丢弃原有内容，然后将新的输出加入到该文件中。

* 打开已有的文件，以接受输出时，默认将它其长度截短为零，因此原来的内容将丢失。

outFile.open("carinfo.txt");

cout<<"Enter the make and model of auto mobile: ";

cin.getline(automobile,50);

cout<<"Enter the model year: ";

cin>>year;

cout<<"Enter the original asking price: ";

cin>>a_price;

d_price=0.913*a_price;

//display information on screen with cout

cout<<fixed;

cout.precision(2);

cout.setf(ios_base::showpoint);

cout<<"Make and model: "<<automobile<<endl;

cout<<"Year: "<<year<<endl;

cout<<"Was asking $"<<a_price<<endl;

cout<<"Now asking $"<<d_price<<endl;

//now do exact same things using outFile instead of cout

outFile<<fixed;

cout.precision(2);

cout.setf(ios_base::showpoint);

outFile<<"Make and mode: "<<automobile<<endl;

outFile<<"Year: "<<year<<endl;

outFile<<"Was asking $"<<a_price<<endl;

outFile<<"Now asing $"<<d_price<<endl;

outFile.close(); //done with file

return 0;

}

第二个程序：读取txt文本的内容
下面程序打开用户指定的文件，读取其中的数字，然后指出文件中包含多少个值以及它们的和与平均值。正确地设计输入循环至关重要。
这个程序我运行的时候出了一个问题，就是未能找到最后结果计算，如下图所示，

正确的运行结果应该是：

很有意思，可以研究哈，我在csdn发帖询问了，可参考其帖子：txt文件读取问题
程序代码如下：

#include "stdafx.h"

#include <iostream>

#include <fstream> //file I/O support

#include <cstdlib> //support for exit()

using namespace std;

const int SIZE =60;

int main(int argc, char* argv[])

{

char filename[SIZE];

ifstream inFile; //object for handling file input

cout<<"Enter name of data file: ";

cin.getline(filename, SIZE);

inFile.open(filename); //associate inFile with a file

if(!inFile.is_open()) //failed to open file

{

cout<<"Could not open the file "<<filename<<endl;

cout<<"Program terminating.\n";

exit(EXIT_FAILURE);

}

double value;

double sum=0.0;

int count=0; //number of items read

inFile>>value; //get first value

while(inFile.good()) //while input good and not at EOF

{

++count; //one more item read

sum+=value; //calculate runing total

//cout<<"第"<<count<<"个数="<<value<<endl;

inFile>>value; //get next value

}

//cout<<value<<endl;

if(inFile.eof())

cout<<"End of file reached.\n";

else if(inFile.fail())

cout<<"Input terminated by data mismatch.\n";

else

cout<<"Input terminated for unknown reason.\n";

if(count==0)

cout<<"No data processed.\n";

else

{

cout<<"Items read: "<<count<<endl;

cout<<"Sum: "<<sum<<endl;

cout<<"Average: "<<sum/count<<endl;

}

inFile.close(); //finished with the file