删除和替换 .txt 文件中的特定行

Question

我正在为与文件处理相关的 C++ 项目苦苦挣扎，需要帮助。

这是我的 movies.txt 文件

SNO, Name, NoOfPeopleLiked
1, The Shawshank Redemption, 77 
2, The Godfather, 20        
3, Into The Wild, 35
4, The Dark Knight, 55      
5, 12 Angry Men, 44     
6, Schindler's List, 33
7, The Lord of the Rings: The Return of the King, 25
8, Pulp Fiction, 23
9, The Good, the Bad and the Ugly, 32   
10, The Lord of the Rings: The Fellowship of the Ring, 56

我想通过输入该行的电影名称来删除该行。对于示例，当我输入电影名称“12 Angry Men”时，应删除整行第 5 行并替换为增加了 NoOfPeopleLiked 的更新行strong> 值从 5, 12 Angry Men, 44 到 5, 12 Angry Men, 45。 每当我输入电影名称时，如何删除该特定行并更新喜欢的值？

---

但是当我输入电影名称时，所有行都被删除，直到第 6 行，输出文件看起来像这样。

---

    , Schindler's List, 33
7, The Lord of the Rings: The Return of the King, 25
8, Pulp Fiction, 23
9, The Good, the Bad and the Ugly, 32   
10, The Lord of the Rings: The Fellowship of the Ring, 56

---

请帮我解决这个问题？ 这是我的代码：

void search()
{
    ifstream file;
    file.open("movies.txt");
    cout << "Enter the name of Movie : " << ' ';
    getline(cin, search_movie);
    if (file.is_open())
    {
        while (getline(file, line, ','))
        {
            if ((line.find(search_movie, 0)) != string::npos)
            {
                file >> liked;
                file >> serial;
                cout << serial << " The movie '" << search_movie << "' has been found in database and " << liked << " people like this movie" << endl;
                cout << "Do you like it as well (y/n)" << ' ';
                char z;
                cin >> z;
                if (z == 'y' || z == 'Y')
                {
                    update(search_movie, file);
                }
            }
        }
    }
    else
    {
        cout << "your file could not be opened" << endl;
    }
    file.close();
}

---

    void update(string search_movie, ifstream& file1)
    {
        ofstream temp;
        string linee;
        temp.open("temp.txt", ios::out);
        while (getline(file1, linee))
        {
            cout << linee << endl;
            if (line.substr(0, search_movie.size()) != search_movie)
            {
                temp << linee << endl;
            }
        }
        file1.close();
        temp.close();
        remove("movies.txt");
        rename("temp.txt", "movies.txt");
    }
};

Answer 1

这是您想要做的一个工作示例：它增加了电影的喜欢数量。它不将整个文件的内容存储到缓冲区中。该文件可能很大，因此可能效率不高。

#include <fstream>
#include <iostream>
#include <string>
 
int main()
{
    std::fstream fileMovies{"sample.txt",
                            std::ios_base::in | std::ios_base::out | std::ios_base::binary};
    if (!fileMovies.is_open())
    {
        std::cerr << "Failed to open file" << std::endl;
        return -1;
    }

    std::string movieName{};
    std::getline(std::cin, movieName);

    std::string line{};
    line.reserve(256);

    long long int pos = fileMovies.tellp();
    for (line; std::getline(fileMovies, line);)
    {
        if (line.find(movieName) != std::string::npos)
            break;
        line.clear();
        pos = fileMovies.tellp();
    }

    if (fileMovies.eof())
    {
        std::cerr << "Failed to find the movie by name" << std::endl;
        return -1;
    }

    long long int curPos = fileMovies.tellp();

    // TODO: check format
    long long int commaPos = line.rfind(',');
    fileMovies.seekp(pos + commaPos + 2);

    int liked = 0;
    fileMovies >> liked;
    fileMovies.seekp(pos + commaPos + 2);
    fileMovies << ++liked;

    return 0;
}

输出：

PS C:\dev\builds\editfile\Release-Visual Studio\bin> cat .\sample.txt
SNO, Name, NoOfPeopleLiked
1, The Shawshank Redemption, 77
2, The Godfather, 20
3, Into The Wild, 35
4, The Dark Knight, 55
5, 12 Angry Men, 44
6, Schindler's List, 33
7, The Lord of the Rings: The Return of the King, 25
8, Pulp Fiction, 23
9, The Good, the Bad and the Ugly, 32
10, The Lord of the Rings: The Fellowship of the Ring, 56
PS C:\dev\builds\editfile\Release-Visual Studio\bin> .\main.exe
Angry
PS C:\dev\builds\editfile\Release-Visual Studio\bin> cat .\sample.txt
SNO, Name, NoOfPeopleLiked
1, The Shawshank Redemption, 77
2, The Godfather, 20
3, Into The Wild, 35
4, The Dark Knight, 55
5, 12 Angry Men, 45
6, Schindler's List, 33
7, The Lord of the Rings: The Return of the King, 25
8, Pulp Fiction, 23
9, The Good, the Bad and the Ugly, 32
10, The Lord of the Rings: The Fellowship of the Ring, 56

请记住，您不能在文件中间添加新字符（你也不能抹去它们）。您只能覆盖当前位置的现有内容。 因此，为了使其正常工作，您应该使用带有尾随空格的喜欢的数量，或使用0045 之类的格式。 另外，请注意您必须使用std::fstream 和标志in | out | binary。为了正确计算当前位置，二进制是必需的。