Deleting a line from c++ file by giving a word - c++

Question

I have made a Quizlet code to save a word with its translation(in Russian) in csv file.
So, the 'add' and 'read' functions work perfectly but I have been trying to make the 'delete' function remove a line when I give a substring of that line.
update: I am trying to copy all the lines except the one that i wanna delete to a new file and then rename it.
but when the new file is created, it is empty!
ex: in the file, line 1: apple яблоко.
input: apple, and then the entire is being deleted.
here is my code: I just have a problem in void quizlet::DeleteWord()
#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

Post-update edit:
My original answer now makes much more sense given what you are trying to do. You should read the whole file in at once, make any additions and deletions in-memory you want, then overwrite the original file with the whole, new, list.
Original answer:
Consider reading the file into memory via a std::map<std::string,std::wstring> instead of a std::vector<std::string> of lines in the file.
Using this approach, adding and deleting a word and its translation is simple.
Adding:
//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);
}
Deleting:
auto found_iter = cards.find(word);
if(found_iter != cards.end()) {
cards.erase(found_iter);
}
Writing it back to the file is as simple as looping over the collection:
for(const auto& [word,translation] : cards) {
fout << word << ' ' << translation << '\n';
}
fout.close();

Answer 2

well, after trying for a long time.
I got this code and it works perfectly with no errors.
thank you all!
#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(std::string);
};
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 token) {
string line;
fstream fin;
fstream fout;
fin.open("words.txt", ios::in);
fout.open("new.txt",ios::out | ios::app);
cin >> token;
vector<string> lines;
while(getline(fin, line)) {
if(line.find(token) == string::npos) {
fout << line << endl;
}
}
fout.close();
fin.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, token;
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(token);
} else {
return 0;
}
}
}