Question

尝试将文字读入＆＃34;牛肉＆＃34;
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中，＆＃34; line＆＃34;
文件永远不会显示，当我手动检查时，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;
}

Answer 1

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;
}

您创建了另一个ofstream对象：

ofstream file1;

这会影响您之前创建过的那个。此外，您现在正在影子的是包含指向"beef.txt"的有效文件指针的对象。使用新的内部范围file1并不指向任何文件，因此写入它不会在"beef.txt"中为您提供任何结果。

删除它以使用正确的对象：

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

Answer 2

std::ofstream仅用于输出，您无法用它读取输入。

std::ifstream仅用于输入，您无法用它写输出。

所以，你需要

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，可以用于输出和输入，具体取决于在调用{{1时是否指定in和/或out标志}}：
```
open()
```

使用ifstream，ofstream和fstream

2 个答案: