Using ifstream, ofstream and fstream

Using ifstream, ofstream and fstream

本文关键字：and fstream ofstream ifstream Using      更新时间：2023-10-16

  1. 试图读取一个单词"牛肉"

  2. 后来进行，然后将文件内容编辑给用户想要的任何内容，这些内容将存储在字符串中，" line"

  3. 该文件永远不会显示，当我手动检查它时，文本文件为空白。

#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;
}

在此片段中：

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

您创建另一个ofstream对象：

ofstream file1;

这会阴影您之前已经创建的那个。此外，您现在正在遮蔽的是包含有效文件指针"beef.txt"的对象。使用新的Inter-Scope file1尚未指向任何文件，因此写入它不会在"beef.txt"中给您任何结果。

将其删除以使用正确的对象：

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

std::ofstream仅用于输出，您无法使用它读取输入。

std::ifstream仅用于输入，您不能用它写输出。

所以，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;
}

  • 使用单个std::fstream变量，可用于输出和输入，具体取决于您在调用open()时是否指定in和/或out标志：

    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;
}
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