I want to pass an fstream object and tokenize the the words. It will always print could not open file in hasNextToken() . May someone help me.
//main.cpp
int main() {
string filename = "input.txt";
fstream inputStream(filename);
Tokenizer t(inputStream);
while (t.hasNextToken()) {
cout << t.nextToken();
}
}
//Tokenizer.h
class Tokenizer {
fstream fin;
public:
Tokenizer(fstream& file)
{
fin << file;
}
bool hasNextToken() {
if (!fin) {
cout << "Could not open file: " << endl;
exit(0);
}
return true;
}
string nextToken() {
string line;
getline(fin, line);
if (fin) {
istringstream sin(line);
string word;
sin >> word;
return word;
}
}
};
Try this:
class Tokenizer {
fstream& fin;
public:
Tokenizer(fstream& file)
: fin(file)
{}
...
}
I'm not sure if this will work, I can't test it right now, but you can do it quickly:
int main() {
string filename = "input.txt";
fstream inputStream(filename, ios::in); // add second argument
// other stuff here
}
Cheers
Related
I want to take more than one line from the data.txt file. I am able to take only the first one. I tried using while loop but it seems that I don't know how to use it in this case.
Edited with while loop:
#include <iostream>
#include <fstream>
using namespace std;
int zapis()
{
fstream file;
string text;
file.open("data.txt", ios::app);
cout << "Type in text that you would like to store: ";
getline(cin, text);
file << text << endl;
file.close();
return 0;
}
int odczyt()
{
fstream file;
string line;
int nr_lini = 1;
file.open("data.txt", ios::in);
if(file.good()==false)
{
cout << "Error occured!";
}
else
{
while(getline(file, line))
{
getline(file, line);
cout << line;
}
}
file.close();
return 0;
}
int main()
{
zapis();
odczyt();
return 0;
}
Why call getline twice in your loop? Also pay attention to the semi-colons
while(getline(file, line));
^
What do you think the semi-colon there does?
This is correct
while (getline(file, line))
{
cout << line;
}
Your code is correct, just loop through the file. Also, you could make the function void, as it always returns 0, with you not doing anything with the return value.
void odczyt(){
fstream file;
string line;
file.open("data.txt", ios::in);
if(!file.good())
{
cout << "Error occured!";
}
else
{
while(getline(file, line);) { // while text file still has lines, you write the line and read next
cout << line;
}
}
file.close();
}
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;
}
}
}
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();
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;
}
}
}
I am trying to add each word from a file to a vector but if I make the size of the vector (500) and I only have 20 words in the file. The size of the vector is still considered 500. How do I fix this?
Am I doing this a bad way? Could this be made simpler?
void loadFile(string fileName)
{
vector<string> fileContents(500);
int p = 0;
ifstream file;
file.open(fileName);
if (!file.is_open()) return;
string word;
while (file >> word)
{
fileContents[p] = word;
p++;
}
for (int i = 0; i < fileContents.size(); i++)
{
cout << fileContents[i] << endl;
}
}
You could also use a more direct approach, copying immediately from the input stream.
std::vector<std::string> loadFile(std::string fileName) {
std::ifstream file(fileName);
assert(file);
std::vector<std::string> fileContents;
std::copy(std::istream_iterator<std::string>(file),
std::istream_iterator<std::string>(),
std::back_inserter(fileContents));
return fileContents;
}
#drescherjm in the comments gave me the correct answer.
void loadFile(string fileName)
{
vector<string> fileContents;
ifstream file;
file.open(fileName);
if (!file.is_open()) return;
string word;
while (file >> word)
{
fileContents.push_back(word);
}
for (int i = 0; i < fileContents.size(); i++)
{
cout << fileContents[i] << endl;
}
}
#include <iostream>
#include <string>
#include <fstream>
using namespace std;
void read();
int main() {
read();
return 0;
}
void read () {
string file("");
string nameOfFile("");
cin >> nameOfFile;
ifstream in (nameOfFile);
while ( !in.eof() ) {
getline(in, file);
cout << file;
cout << endl;
}
cout << file;
in.close();
}
How come this isn't working, I'm trying to make it so i can type in which file i want to read?
I'm really new to C++, sorry if this is an obvious fix.
You have to change
ifstream in (nameOfFile);
with
ifstream in (nameOfFile.c_str());
because the default constructor for ifstream does not accept a std::string as an argument, it needs a char *. Hence, use the function std::string::c_str() to convert a std::string into a char *.
A little feedback:
void read () {
string file(""); // you don't need the ("") bit; empty by default,
// and "file" is a terrible choice of identifier as
// it sounds more like an ifstream than a string
// used to hold one line from the file.
// I tend to use "string line;" for this.
string nameOfFile(""); // ditto
cin >> nameOfFile; // you should test for success of input, like this:
// if (!cin >> nameOfFile) {
// std::cerr << "error reading filename from stdin\n";
// exit(1);
// }
ifstream in (nameOfFile); // test for success getting file open like this:
// if (ifstream in(nameofFile))
// {
while ( !in.eof() ) { // NEVER check eof before attempting input, instead:
getline(in, file); // while (getline(in, file))
cout << file; // cout << file << endl; // can "chain"
cout << endl; // }
// else
// std::cerr << "couldn't open " << nameOfFile
// << '\n';
} // no need for extra cout nor explicit close, as
cout << file; // the ifstream destructor closes anyway.
in.close();
}
You need to open the ifstream usign in.open(), and hendle the case where file does not exist as well. here is the function:
void read() {
string file("");
string fileContent = "";
string nameOfFile("");
cin >> nameOfFile;
ifstream in(nameOfFile.c_str());
in.open(nameOfFile, ios::in);
if (in){
while (!in.eof()) {
getline(in, file);
fileContent += file;
}
cout << fileContent;
in.close();
}
else {
cout << "Could not open file.";
}
}
I want to open a file for reading then output what is in that .txt file, any suggestion on my code?
string process_word(ifstream &word){
string line, empty_str = "";
while (!word.eof()){
getline(word, line);
empty_str += line;
}
return empty_str;
}
int main(){
string scrambled_msg = "", input, output, line, word, line1, cnt;
cout << "input file: ";
cin >> input;
ifstream inFile(input);
cout << process_word(inFile);
}
Instead of:
while (!word.eof()) {
getline(word, line);
empty_str += line;
}
do:
while ( std::getline(word, line) ) {
empty_str += line;
}
and it would be also wise to give your variables more appropriate names.
Your function can be simplified to:
#include <iterator>
std::string process_word(std::ifstream& word)
{
return std::string{std::istream_iterator<char>{word},
std::istream_iterator<char>{}};
}
int main()
{
string input;
std::cin >> input;
std::ifstream inFile(input);
std::cout << process_word(inFile);
}