QFileInfo::birthTime not updated each time?

Maluna34

Hello,

I figured out that after creating multiple times a file, sometimes the birth time is older than the real one.
I have the following code, in which I create the same file three times:

#include <QCoreApplication>

#include <QDateTime>
#include <QDebug>
#include <QFile>
#include <QFileInfo>
#include <QThread>

void createFile(const QString& fileName)
{
    QFile file { fileName };
    file.open(QIODevice::WriteOnly);
}

int main(int argc, char *argv[])
{
    QCoreApplication app(argc, argv);

    const QString fileName { "test.txt" };

    qDebug() << "[" << QDateTime::currentDateTime() << "] 1/-" << QFile::exists(fileName);
    QThread::msleep(500);
    createFile(fileName);
    qDebug() << "\tCreated:" << QFileInfo(fileName).birthTime();
    qDebug() << "\tRemoved:" << QFile::remove(fileName);

    qDebug() << "[" << QDateTime::currentDateTime() << "] 2/-" << QFile::exists(fileName);
    QThread::msleep(500);
    createFile(fileName);
    qDebug() << "\tCreated:" << QFileInfo(fileName).birthTime();
    qDebug() << "\tRemoved:" << QFile::remove(fileName);

    qDebug() << "[" << QDateTime::currentDateTime() << "] 3/-" << QFile::exists(fileName);
    QThread::msleep(500);
    createFile(fileName);
    qDebug() << "\tCreated:" << QFileInfo(fileName).birthTime();
    qDebug() << "\tRemoved:" << QFile::remove(fileName);

    return app.exec();
}

And here is the result:

[ QDateTime(2021-07-27 09:32:57.593 Paris, Madrid (heure d’été) Qt::LocalTime) ] 1/- false
	Created: QDateTime(2021-07-27 09:32:58.100 Paris, Madrid (heure d’été) Qt::LocalTime)
	Removed: true
[ QDateTime(2021-07-27 09:32:58.100 Paris, Madrid (heure d’été) Qt::LocalTime) ] 2/- false
	Created: QDateTime(2021-07-27 09:32:58.100 Paris, Madrid (heure d’été) Qt::LocalTime)
	Removed: true
[ QDateTime(2021-07-27 09:32:58.613 Paris, Madrid (heure d’été) Qt::LocalTime) ] 3/- false
	Created: QDateTime(2021-07-27 09:32:58.100 Paris, Madrid (heure d’été) Qt::LocalTime)
	Removed: true

For the last file, the birth time is exactly the same as the previous one, and less than the currentTime before creation. :o
Before: 09:32:58.613
Birth time: 09:32:58.100

Do you have any idea?
Thanks a lot!!

KroMignon

@Maluna34 said in QFileInfo::birthTime not updated each time?:

Do you have any idea?

Did you notice that file always have same creation timestamp?
I am quiet sure, this is because you are always recreating the same file, and the file system layer of your OS is optimizing it, to avoid to always create a new file descriptor.

Nothing to do with Qt, it is system relevant.