How to recursively write data to a text file in C++/ Qt - c++

Question

I have a C++\Qt program that scans the files in a particular directory. I'm trying to write the paths to the files contained therein in a text file, but all I've managed to do is write the path to the last file.
void ScanDir::qDirIteratorScanner(QString path)
{
QDirIterator it(path, QStringList() << "*.mp4", QDir::Files, QDirIterator::Subdirectories);
while (it.hasNext())
{
WriteToFile writeToFile(path, it.next());
qDebug() << "it.next()";
}
}
...
WriteToFile::WriteToFile(QString path, QString data)
{
path += "/Data.txt";
QFile file(path);
if (file.open(QFile::ReadWrite)) {
QTextStream stream(&file);
stream << data << endl;
}
}
How can I write all the paths into the text file?

Answer 1

You're creating a QFile in read/write mode at each call of WriteToFile: this is truncating the contents of the file, so only contents written by the last call will remain.
Try:
void ScanDir::qDirIteratorScanner(QString path)
{
QDir dir(path);
QFile file(dir.absoluteFilePath("Data.txt"));
if (file.open(QFile::ReadWrite)) {
QTextStream stream(&file);
QDirIterator it(
dir,
QStringList() << "*.mp4",
QDir::Files,
QDirIterator::Subdirectories
);
while (it.hasNext())
{
stream << it.next() << endl;
}
}
}
Here the file is opened only once. If you want/need to keep a function WriteToFile, pass stream as an additional parameter (by reference).
Note:
As proposed by Simon Kraemer in the comments, I used QDir::absoluteFilePath as it makes it easier to prevent missing or accidental slashes in the path.
An alternative to keep your design may be to use QFile::Append mode:
void ScanDir::qDirIteratorScanner(QString path)
{
QDir dir(path);
// reset the file
{
QFile file(dir.absoluteFilePath("Data.txt"));
file.open(QFile::ReadWrite);
}
QDirIterator it(
dir,
QStringList() << "*.mp4",
QDir::Files,
QDirIterator::Subdirectories
);
while (it.hasNext())
{
WriteToFile writeToFile(path, it.next());
qDebug() << "it.next()";
}
}
WriteToFile::WriteToFile(QString path, QString data)
{
QDir dir(path);
QFile file(dir.absoluteFilePath("Data.txt"));
if (file.open(QFile::Append)) {
QTextStream stream(&file);
stream << data << endl;
}
}

Answer 2

Each time you open the file and write one line to it, overwriting whatever is in the file. Instead, try opening it in append mode, this should cause whatever you write to be added at the end of the file.
QTextStream stream(&file,QIODevice::Append);

Answer 3

You must open the file in "append" mode, otherwise you will override its content every time you open the file:
file.open(QFile::Append)
2 remarks to your code:
Writing to a file from a constructor seems questionable. Why don't you just declare a function?
Why don't you open the file just once?
void ScanDir::qDirIteratorScanner(QString path)
{
QFile file(QDir(path).absoluteFilePath("Data.txt"));
if(file.open(QFile::WriteOnly))
{
QTextStream stream(&file);
QDirIterator it(path, QStringList() << "*.mp4", QDir::Files, QDirIterator::Subdirectories);
while (it.hasNext())
{
stream << it.next() << endl;
qDebug() << "it.next()";
}
}
}

Answer 4

It would be most efficient to move the file opening and writing to qDirIteratorScanner() instead of WriteToFile(). This way you can open the file, write everything, then close the file.
What you have now is you keep on opening (and overwriting) the same file on every iteration. That's why you are only left with the last write. Alternatively, you could open the file with the QIODevice::Append flag, but that's just unnecessary operations compared to the first suggestion, where you will open the file only once to write everything.