C++文件的输出、输入

输出到文件

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

int main()
{
    char automobile[50];
    int year;
    double a_price;
    double d_price;

    ofstream outFile;
    outFile.open("carinfo.txt");

    cout<<"Enter the make and model of automobile: ";
    cin.getline(automobile,50);
    cout<<"Enter the model year: ";
    cin>>year;
    cout<<"Enter the orignal 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 nad model: "<<automobile<<endl;
    cout<<"Year: "<<year<<endl;
    cout<<"Was asking $"<<a_price<<endl;
    cout<<"Now asking $"<<d_price<<endl;

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

    outFile<<fixed;
    outFile.precision(2);
    outFile.setf(ios_base::showpoint);
    outFile<<"Make nad model: "<<automobile<<endl;
    outFile<<"Year: "<<year<<endl;
    outFile<<"Was asking $"<<a_price<<endl;
    outFile<<"Now asking $"<<d_price<<endl;

    outFile.close();
    return 0;
}

输入到文件

#include <iostream>
#include <fstream>
#include <cstdlib>

const int SIZE = 60;
using namespace std;
int main()
{
    char filename[SIZE];
    ifstream inFile;
    cout<<"Enter name of data file: ";
    cin.getline(filename,SIZE);
    inFile.open(filename);
    if(!inFile.is_open())
    {
        cout<<"Couldnot open  the file "<<filename<<endl;
        cout<<"Program terminating.\n";
        exit(EXIT_FAILURE);
    }
    double value;
    double sum=0.0;
    int count =0;

    inFile>>value;
    while(inFile.good())
    {
        ++count;
        sum+=value;
        inFile>>value;
    }
    if(inFile.eof())
    cout<<"End of filereached.\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();
    return 0;
}