使用ifstream、ofstream和fstream-C/C++问题

Using ifstream, ofstream and fstream(使用ifstream、ofstream和fstream)

本文介绍了使用ifstream、ofstream和fstream的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

正在尝试将"beave"一词读入文件
稍后将文件内容编辑为用户想要的内容，并将其存储在字符串"line"中
文件从不显示，当我手动检查时，文本文件为空。

#include "stdafx.h"
#include <iostream>
#include <fstream>
#include <string>
using namespace std;

int main()
{
    string line = { " " };
    ofstream file1;
    file1.open("beef.txt");
    file1 << "beef" << endl;
    file1.close();
    file1.open("beef.txt");

    if (file1.is_open())
    {
        cout << "Enter what you would like to be contained in the file" << endl;
        cin >> line;
        ofstream file1;
        file1 << line << endl;
    }

    return 0;
}

推荐答案

Astd::ofstream仅用于输出，不能用它读取输入。

Astd::ifstream仅用于输入，您不能用它编写输出。

因此，您需要

使用单独的std::ofstream和std::ifstream变量：

int main()
{
    ofstream out_file;
    ifstream in_file;
    string line;

    out_file.open("beef.txt", ios_base::trunc);
    if (out_file.is_open())
    {
        out_file << "beef" << endl;
        out_file.close();
    }

    in_file.open("beef.txt");
    if (in_file.is_open())
    {
        getline(in_file, line);
        in_file.close();

        cout << "File contains:" << endl;
        cout << line << endl;
    }

    cout << "Enter what you would like to be contained in the file" << endl;
    getline(cin, line);

    out_file.open("beef.txt", ios_base::trunc);
    if (out_file.is_open())
    {
        out_file << line << endl;
        out_file.close();
    } 

    in_file.open("beef.txt");
    if (in_file.is_open())
    {
        getline(in_file, line);
        in_file.close();

        cout << "File now contains:" << endl;
        cout << line << endl;
    }

    return 0;
}

根据调用open()时是否指定了in和/或out标志，使用一个std::fstream变量，该变量可同时用于输出和输入：

int main()
{
    fstream file;
    string line;

    file.open("beef.txt", ios_base::out | ios_base::trunc);
    if (file.is_open())
    {
        file << "beef" << endl;
        file.close();
    }

    file.open("beef.txt", ios_base::in);
    if (file.is_open())
    {
        getline(file, line);
        file.close();

        cout << "File contains:" << endl;
        cout << line << endl;
    }

    cout << "Enter what you would like to be contained in the file" << endl;
    getline(cin, line);

    file.open("beef.txt", ios_base::out | ios_base::trunc);
    if (file.is_open())
    {
        file << line << endl;
        file.close();
    }

    file.open("beef.txt", ios_base::in);
    if (in_file.is_open())
    {
        getline(in_file, line);
        in_file.close();

        cout << "File now contains:" << endl;
        cout << line << endl;
    }

    return 0;
}

这篇关于使用ifstream、ofstream和fstream的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持编程学习网！