[SOLVED] QTemporaryFile - strange behavior

_rth_

Hello.

I have problem with QTemporaryFile location. In my app, in some point I need to clear the temp file content. I have used the simplest way: remove file and initialize it again. However after this step, QTemporaryFile class changes location, where temp file is created.

Here is simple app, which simulates the problem:

#include <QCoreApplication>
#include <QTemporaryFile>
#include <QDebug>

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

    QTemporaryFile tmpFile;

    if (tmpFile.open())
        qDebug() << tmpFile.fileName();

    tmpFile.remove();

    if (tmpFile.open())
        qDebug() << tmpFile.fileName();

    //return a.exec();
    return 0;
}

And here is the result:

"C:/Users/theuerom/AppData/Local/Temp/tmpfiletest.Hp3912"
"C:/Qt5_projects/build-tmpfiletest-Desktop_Qt_5_4_1_MinGW_32bit-Debug/.gq3912"

Is that a bug? Or am I doing something terribly wrong?

koahnig

@_rth_

This seems really strange.
You could check with QDir::tempPath() to check the default temp file location.

Also you can check in JIRA if there is a known bug.

_rth_

QDir::tempPath() seems to be ok.

Actually I have solved this problem using file template, which contains QDir::tempPath();

#include <QCoreApplication>
#include <QTemporaryFile>
#include <QDir>
#include <QDebug>

void printFile(const QString& name)
{
    QFile file(name);
    if (file.open(QIODevice::ReadOnly)) {
        qDebug() << file.readAll();
        file.close();
    }
}

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

    qDebug() << QDir::tempPath();

    QString templ = QString("%1/something_XXXXXX").arg(QDir::tempPath());

    QTemporaryFile tmpFile;
    tmpFile.setFileTemplate(templ);

    if (tmpFile.open()) {
        qDebug() << tmpFile.fileName();

        tmpFile.write("1st attempt");
        tmpFile.flush();
    }

    printFile(tmpFile.fileName());

    tmpFile.remove();

    tmpFile.setFileTemplate(templ);
    if (tmpFile.open()) {
        qDebug() << tmpFile.fileName();

        tmpFile.write("2nd attempt");
        tmpFile.flush();
    }

    printFile(tmpFile.fileName());

    //return a.exec();
    return 0;
}

SGaist

Hi,

It still feels like a bug, you really should take a look at the bug report system like @koahnig suggested

ChrisW67

https://bugreports.qt.io/browse/QTBUG-2557 seems related

Rather than remove() the file and create a new one you should be able to resize(0) and continue to use the same temporary file.

_rth_

I have quickly gone through existing bugs reported for QTemporaryFile and nothing related found. So I have created new bug: https://bugreports.qt.io/browse/QTBUG-46156. IMO its better to have a few duplicates, that not reported at all :)

BTW, the resize(0) works fine.