C++ 文件

学习C++ – C++文件

写入文本文件

以下代码从用户收集信息，将输出发送到显示器，然后将相同的输出发送到文件。

#include <iostream>
#include <fstream>                  // for file I/O
using namespace std;
int main()
{
    char automobile[50];
    int year;
    double a_price;

    ofstream outFile;               // create object for output
    outFile.open("test.txt");    // associate with a file

    cout << "Enter the make and model: ";
    cin.getline(automobile, 50);
    cout << "Enter the model year: ";
    cin >> year;
    cout << "Enter the price: ";
    cin >> a_price;

    // display information
    cout << fixed;
    cout.precision(2);
    cout.setf(ios_base::showpoint);
    cout << "Model: " << automobile << endl;
    cout << "Year: " << year << endl;
    cout << "$" << a_price << endl;

    //File
    outFile << fixed;
    outFile.precision(2);
    outFile.setf(ios_base::showpoint);
    outFile << "Model: " << automobile << endl;
    outFile << "Year: " << year << endl;
    outFile << "$" << a_price << endl;

    outFile.close();                // done with file
    return 0;
}

上面的代码生成以下结果。

从文本文件读取

下面的程序打开用户指定的文件，从文件中读取数字，并报告值的数量，它们的总和及其平均值。

#include <iostream>
#include <fstream>        
#include <cstdlib>        
using namespace std;
const int SIZE = 60;
int main()
{
    char filename[SIZE];
    ifstream inFile;        // object for handling file input

    cout << "Enter file name:";
    cin.getline(filename, SIZE);
    inFile.open(filename);  // associate inFile with a file
    if (!inFile.is_open())  // if failed to open file, error out
    {
        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;       
        inFile >> value;    // get next value
    }
    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
    return 0;
}

上面的代码生成以下结果。