c++ - 通过给出一个词从c++文件中删除一行

Question

我制作了一个 Quizlet 代码，用于将单词及其翻译(俄语)保存在 csv 文件中。因此，“添加”和“读取”功能完美运行，但我一直在尝试让“删除”功能在我给出该行的子字符串时删除该行。

更新:我正在尝试将除我想删除的行之外的所有行复制到一个新文件中，然后重命名它。但是当创建新文件时，它是空的!

例如:在文件中，第 1 行:apple яблоко。

输入:apple，然后整个被删除。

这是我的代码:我只是在 void quizlet::DeleteWord() 中遇到问题

#include <string>
#include <iostream>
#include <vector>
#include<fstream>
#include <sstream>
#include<cstdlib>
using namespace std;

class quizlet {
private:
    std::string filename;
    std::vector<std::string> lines;

public:
    quizlet(std::string filename) : filename(filename) {}

    void AddWord(std::string, std::string);
    vector<string> ReadAllWords();
    void DeleteWord();
};

void quizlet::AddWord(std::string word, std::string translation) {
   cout << "Write a word and its translation separated by a space:" << std::endl;
   cin >> word >> translation;


   // file pointer
    fstream fout;

    // opens an existing csv file or creates a new file.
    fout.open("words.txt",ios::out | ios::app);
    // Insert the data to file
    fout <<word<<" "<<translation<<endl;

    std::cout << "Saved new card: " << word << "/" << translation << std::endl;
}

vector<string> quizlet::ReadAllWords() {

    // File pointer
    fstream fin;

    // Open an existing file
    fin.open("words.txt", ios::in);




    // Read the Data from the file
    // as String Vector
    vector <string> rows;
    string line, word, temp;


    while (getline(fin, line)) {

        cout << line << std::endl;
        rows.push_back(line);
        stringstream s(line);

    }

    return rows;







   }


void quizlet::DeleteWord() {

    string line;
    fstream fin;
    fstream fout;
    fin.open("words.txt", ios::in);
    fout.open("new.txt",ios::out | ios::app);
    string token;
    cin>>token;

    vector <string> lines;
    while (getline(fin, line)) {
        if (line.find(token) != string::npos) {
            cout << line << endl;
            fin << line << endl;
            cout<<"the line has been deleted!";
            //remove (line);
        }
    }

    fin.close();
    fout.close();
    remove("words.txt");
    rename("new.txt", "words.txt");
    cout << "\nChanges has Successfully been made...... Data Saved\n" << endl;

}




int main() {
    auto Quizlet = quizlet("words.txt");
    string word, translation;
    while (true) {
        std::string command;
        std::cin >> command;



        if (command == "add") {

            Quizlet.AddWord(word, translation);

        } else if (command == "read") {
            Quizlet.ReadAllWords();

        }
        else if (command == "delete") {
            Quizlet.DeleteWord();

        }



        else {
            return 0;
        }
    }
}

Answer 1

更新后编辑:

鉴于您正在尝试做的事情，我原来的答案现在更有意义了。您应该立即读取整个文件，在内存中进行任何您想要的添加和删除，然后用整个新列表覆盖原始文件。

原答案:

考虑通过 std::map<std::string,std::wstring> 将文件读入内存而不是 std::vector<std::string>文件中的行数。

使用这种方法，添加和删除单词及其翻译很简单。

添加:

//if-guard only needed if you want to protect against overwriting already-existing words.
auto found_iter = cards.find(word);
if(found_iter == cards.end()) {
    cards.insert_or_assign(word, translation);
}

删除:

auto found_iter = cards.find(word);
if(found_iter != cards.end()) {
    cards.erase(found_iter);
}

将其写回文件就像遍历集合一样简单:

for(const auto& [word,translation] : cards) {
    fout << word << ' ' << translation << '\n';
}
fout.close();