OK, so I am using QT Creator for C++ and I am making a function that allows me to parse through the CSV file that I have named getExcelFile. Everything else is working fine but my code will not enter my while loop for some reason which is driving me crazy. Some suggestions would be helpful! Thanks.
void Widget::getExcelFile(){
//Name of the Qfile object.
//filename is the directory of the file once it has been selected in prompt
QFile thefile(filename);
//If the file isn't successfully open
if (thefile.open(QIODevice::ReadOnly | QIODevice::Text)){
qDebug() << "File opened successfully";
//Converts text file to stream
QTextStream in(&thefile);
fileContent=in.readAll();
QString line;
while (!in.atEnd()){
//line = textStream.readLine();//reads line from file
//Will not enter this loop for some odd reason.
qDebug() << "This text does not print out";
}
}
qDebug() << "This prints out successfully";
ui->textEdit->setPlainText(fileContent);
}
You did in.readAll(), after that call in.atEnd() will return true. Either remove in.readlAll() or while loop, why do you need both?
Related
So, I get infinite cycle while trying to read lines from file (line by line). I was trying to use do{}while(); cycle like that:
QTextStream stream(stdin);
QString line;
do {
line = stream.readLine();
} while (!line.isNull());
but I get empty string.
Sure, I checked file path (it is right). I was trying to use /Users/user/tts.txt path but without changes. I was trying to read other files (like m3u). And it's not working on macOS Catalina, Windows 10, Linux (Debian).
So, why did I get infinite cycle?
QStringList Manager::GetLinesFromFile(const QString &nameOfFile)
{
QStringList lines = {};
//path to file
const QString path = QCoreApplication::applicationDirPath() + "/bin/" + "tts.txt";
//"/Users/user/tts.txt"
QFile buffer;
buffer.QFile::setFileName(path);
#ifndef Q_DEBUG
qDebug() << path;
#endif
if(buffer.QFile::exists())
{
if(!buffer.QIODevice::open(QIODevice::ReadOnly))
{
#ifndef Q_DEBUG
qCritical() << "error: can't open file";
#endif
}
else
{
QTextStream stream(&buffer);
// both conditions
// (!stream.QTextStream::atEnd())
while(!buffer.QFileDevice::atEnd())
lines.QList::push_back(stream.QTextStream::readLine());
buffer.QFile::close();
}
}
else
{
#ifndef Q_DEBUG
qCritical() << "error: file not exists";
#endif
}
return lines;
}
Have a look at the QTextstream documentation https://doc.qt.io/qt-5/qtextstream.html. There is an example of reading line by line. Your while loop should read until the stream reaches the end of the buffer and many of the in built read functions will return false when his happens
So, I got it. I opened the file incorrectly.
I was using:
if(!file.QIODevice::open(QIODevice::ReadOnly))
but it should be like that:
if(!file.QFile::open(QFile::ReadOnly))
So I am trying to convert a QFile into a QString by doing the following:
void MainWindow::openTemplateFile(QString location)
{
if (location.isEmpty())
return;
else
{
QString variable;
templateFile.setFileName(location);
if (!templateFile.open(QFile::ReadOnly | QFile::Text))
{
QMessageBox::information(this, "Unable to open template",
templateFile.errorString());
return;
}
else // file opened and ready to read from
{
QTextStream in(&templateFile);
QString fileText = in.readAll();
qDebug() << templateFile.size() << in.readAll();
}
}
}
However, in I get the following result in the debug console:
48 ""
templateFile does exist and is part of the MainWindow class. This is also simplified code - in the actual program I read chars from the file and it works correctly. The location string is a result of the QFileDialog::getOpenFileName function, which I open a txt file with.
You call readAll() twice. The second time, the stream is positioned at end-of-file, and so readAll() has nothing to read and returns an empty string. Print fileText in your debug output instead.
I have a program which opens the same file several times.
I want to check before open any file if this file currently is open or not because I don't want to open the same file several times.
Is there a built-in function which can check if the file is currently open or any other way can do that?
The Code:
QString openFilePath = QFileDialog::getOpenFileName(this->mainWindow, "Open File");
if(openFilePath == ""){
return;
}
QFile openFile(openFilePath);
if(!openFile.open(QFile::ReadWrite)){
QMessageBox::critical(this->mainWindow, "Can't Open file", "Can't access to the file.");
}
QTextStream fileContent(&openFile);
QFileInfo fileInfo(openFile);
this->createEmptyFile(fileInfo.fileName());
this->txtEditor->setText(fileContent.readAll());
It seems to me that your question has really nothing to do with file opening in the programmatic sense, but is exclusively related to your application logic. You need to internally keep a list of all currently open files (in the sense that your GUI is showing such file), and do a check if the user opens a new file.
existing question
also you can try the hack) I dont know would it works or not, but: in the
void QFile::setFileName(const QString &name)
function overview QFile you can see that
Do not call this function if the file has already been opened.
Hmm) what if try to rename it in try catch to avoid crashing and if the renaming done, rename it again and open?) so you can try.
Regular file open, say for append, depending on the function, will usually return NULL or raise an exception if the file is already open. There are stateless file systems where this approach may not work.
std::fstream fs;
try {
fs.open("lk.txt", std::fstream::in | std::fstream::out | std::fstream::app);
fs << "We're way beyond the boundaries of the Pride Lands.";
} catch (const std::ios_base::failure &ex) {
// Something happened
std::cerr << ex.what() << std::endl;
}
fs.close();
In some file systems there are also shared open modes, which will explicitly let you concurrently reopen the file and do what you want with no errors generated.
here is the solution to your problem:-
is_open()
Scope:
std::ofstream::is_open
1.it Check if file is open or not?
2.it returns whether the stream is currently associated to a file
3.it is public member function of fstream.
4.parameters -none
Sample Code:
#include <iostream>
#include <fstream> // std::ofstream
int main ()
{
std::ofstream ofs;
ofs.open ("hye.txt");
if (ofs.is_open())
{
ofs << "hellow world";
cout << "successfully written to file";
ofs.close();
}
else
{
cout << "Error opening file";
}
return 0;
}
output:
successfully written to file
I am trying to follow the tutorial here and serialize Qt objects. Here is my code:
QFile file("/Users/kaustav/Desktop/boo.dat");
if (!file.open(QIODevice::WriteOnly)) {
qDebug() << "Cannot open file for writing: "
<< qPrintable(file.errorString()) << endl; //no error message gets printed
return 0;
}
QDataStream out(&file); // we will serialize the data into the file
out.setVersion(QDataStream::Qt_5_3); //adding this makes no difference
out << QString("the answer is"); // serialize a string
out << (qint32)42;
When I run this program, the file gets created in my desktop all right, but its size is 0 kB, it is blank. Naturally, when I then try this:
QFile file("/Users/kaustav/Desktop/boo.dat");
file.open(QIODevice::ReadOnly);
QDataStream in(&file); // read the data serialized from the file
in.setVersion(QDataStream::Qt_5_3);
QString str;
qint32 w;
in >> str >> w;
I get a blank string in str. What am I doing wrong? If of any help, I am using Qt Creator 3.1.1 based on Qt 5.2.1.
Check if there are any errors returned when calling open and ensure you close the file with file.close() when you're finished with it.
As you're using Qt 5, you should really use QSaveFile instead, when saving the data.
How to write Combobox current text in a preexisting text file in hard drive? Here is my code:
void second::on_pushButton_4_clicked()
{
QFile file("vik.txt");
if (!file.open(QIODevice::WriteOnly | QIODevice::Text))
return;
QTextStream out(&file);
out << ui->comboBox_5->currentText() << "\n";
}
Maybe you forgot to close the file
void second::on_pushButton_4_clicked()
{
// Get comboBox text value
QString txt = ui->comboBox_5->currentText();
// Open file for writing
QFile file("vik.txt");
file.open(QIODevice::WriteOnly | QIODevice::Text);
QTextStream out(&file);
// Write in file
out << txt << "\n";
// Close file
file.close();
}
You have several issues in your code, let me enumerate them one-by-one:
You need this flag for "overwrite" as per your comment:
QIODevice::Truncate 0x0008 If possible, the device is truncated before it is opened. All earlier contents of the device are lost.
More importantly, have you checked whether the method returns after open with some error? If it does, please print out file.errorString() there:
if (!file.open(QIODevice::WriteOnly | QIODevice::Text)) {
qDebug() << file.errorString();
return;
}
On the most important note, you are likely facing the issue that the file is not in your current working directory. If the file resides beside the application executable, please change the corresponding line into your code to this:
QFile file(QCoreApplication::applicationDirPath() + "/vik.txt");