QTemporaryFile - can't open

qwe3

@jsulm When I have:

    QTemporaryFile *tmp = new QTemporaryFile;
    tmp->open();
    tmp->setAutoRemove(true);

    QProcess

    QFile file(tmp->fileName());
    qInfo()<<file.open(QIODevice::ReadOnly);
    qInfo()<<file.errorString();
    qInfo()<<file.fileName();
    QTextStream ts(&file);
    while(!ts.atEnd())
   {
      QString line = ts.readLine();
      qDebug()<<"text";
   }

and I open that tmp->fileName() in windows explorer by notepad, it is empty. When I setFileName and add ".txt" it is not empty :D

Debug before while loop says:
true
"Unknown error"
"C:/Users/myUserName/AppData/Local/Temp/myAppName.nkUyod"

But I still don't see "text". It is in while loop.

jsulm

@qwe3 said in QTemporaryFile - can't open:

QFile file(tmp->fileName());

There is no need for QFile as QTemporaryFile IS QFile.
Now you simply try to open a file which is already open.
Remove file and use tmp directly.

Also atEnd() will probably return true as your temp file is empty.

And what is this QProcess in your code snippet?

qwe3

@jsulm Now my code is:

    QTemporaryFile *tmp = new QTemporaryFile;
    tmp->open();
    tmp->setAutoRemove(true);

    QProcess *proc = new QProcess;
    QString cmdCommand = R"(cmd /c "net use > )"+tmp->fileName()+R"(")";
    proc->start(cmdCommand);
    qDebug()<<tmp->open();
    qDebug()<<tmp->size();

    QTextStream ts(tmp);
    while(!ts.atEnd())
    {

    }

qDebug says:
true
0

I know that cmdCommand is good - when I add ".txt" to file, and open that file in Windows Explorer I see the result of that command.

jsulm

@qwe3 Are you aware that you have to wait until the process has finished before you can access the content of the file? You can't just immediately read the file. And I doubt on Windows this will work as the process probably will not be able to write to this file as it is open in your app. You should call close() before proc->start(cmdCommand); and open again when the process finished.
Either use https://doc.qt.io/qt-5/qprocess.html#waitForFinished or https://doc.qt.io/qt-5/qprocess.html#finished

"when I add ".txt" to file, and open that file in Windows Explorer I see the result of that command" - it will work same way without adding .txt if you explicetly open that file in a text editor. Again: file extension does NOT influence the format of the data in the file. It only tells Windows explorer what application to use to pen it if you double click on it. If you don't believe me do this: change the file extension of a picture to .txt and double click on it...

qwe3

@jsulm You are right. But...

I do something like:
tmp->fileName(), wait 10 seconds, don't delete tmp and open it in windows Explorer - I still see only empty File. Of course my app is still working.

"net use" is very simple command

jsulm

@qwe3 said in QTemporaryFile - can't open:

wait 10 seconds

How do you wait? Did you close the tmp file before starting the process as I suggested?
Also, if using QProcess please do proper error handling to see what happens: https://doc.qt.io/qt-5/qprocess.html#errorOccurred
https://doc.qt.io/qt-5/qprocess.html#readyReadStandardError
https://doc.qt.io/qt-5/qprocess.html#error
https://doc.qt.io/qt-5/qprocess.html#exitCode

You actually do not need a file here at all to get the output of that command as you can use https://doc.qt.io/qt-5/qprocess.html#readyReadStandardOutput and https://doc.qt.io/qt-5/qprocess.html#readAllStandardOutput

QProcess proc;
QString cmdCommand = "cmd";
QStringList param;
param << "/c" << "net" << "use";
proc.start(cmdCommand, param);
proc.waitForFinished();
QByteArray output = proc.readAllStandardOutput();

Also, the way you're currently using QProcess is wrong: do not pass command AND parameter in a single string! See the code above for how it should be (and check documentation).

qwe3

@jsulm Of course I know readAllStandardOutput, but I have to write data to file and from file get data to QTextStream.
Ok, so when I have code something like ( here I don't use temporary File - textFile5 isn't exists - so it's created ):

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QDebug>
MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    QFile someFile(R"(C:\Users\myUserName\Desktop\textFile5)");

    tmpFile = new QTemporaryFile;
    tmpFile->open();
    proc = new QProcess;
    connect(proc, SIGNAL(errorOccurred(QProcess::ProcessError )), this, SLOT(errorOccurredSlot(QProcess::ProcessError)));
    proc->start(R"(cmd /c "net use > )"+someFile.fileName()+R"(")");
    proc->waitForFinished();

    qInfo()<<proc->exitCode();
    tmpFile->close();
    qInfo()<<tmpFile->fileName();
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::errorOccurredSlot(QProcess::ProcessError error)
{
    qInfo()<<error;
}

Everything is ok - I open in windows explorer C:\Users\myUserName\Desktop\textFile5 and there is a data and exitCode is 0.

Now I change my code to:

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QDebug>
MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    QFile someFile(R"(C:\Users\myUserName\Desktop\text5)");

    tmpFile = new QTemporaryFile;
    tmpFile->open();
    proc = new QProcess;
    connect(proc, SIGNAL(errorOccurred(QProcess::ProcessError )), this, SLOT(errorOccurredSlot(QProcess::ProcessError)));
    proc->start(R"(cmd /c "net use > )"+tmpFile->fileName()+R"(")");
    proc->waitForFinished();

    qInfo()<<proc->exitCode();
    tmpFile->close();
    qInfo()<<tmpFile->fileName();
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::errorOccurredSlot(QProcess::ProcessError error)
{
    qInfo()<<error;
}

I only change one line: proc->start(R"(cmd /c "net use > )"+tmpFile->fileName()+R"(")");

Now exitCode is 1 ( so it's different ) and temporary file is empty.

jsulm

@qwe3 said in QTemporaryFile - can't open:

Now exitCode is 1 ( so it's different )

That's why I suggested to implement proper error handling...
And I think this is now third time I write it: close the temp file before starting process!

qwe3

@jsulm Ok, I close temp file before starting process.

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QDebug>
MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    tmpFile = new QTemporaryFile;
    tmpFile->open();
    proc = new QProcess;
    tmpFile->close();
    connect(proc, SIGNAL(errorOccurred(QProcess::ProcessError )), this, SLOT(errorOccurredSlot(QProcess::ProcessError)));
    connect(proc, SIGNAL(finished(int , QProcess::ExitStatus )), this, SLOT(finishedSlot(int , QProcess::ExitStatus )));
    proc->start(R"(cmd /c "net use > )"+tmpFile->fileName()+R"(")");
    proc->waitForFinished();

    qInfo()<<proc->exitCode();

    qInfo()<<tmpFile->fileName();
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::errorOccurredSlot(QProcess::ProcessError error)
{
    qInfo()<<"error"<<error;
}

void MainWindow::finishedSlot(int exitCode, QProcess::ExitStatus exitStatus)
{
    qInfo()<<"exitCode in Slot"<<exitCode;
    qInfo()<<"exit Status in Slot"<<exitStatus;
}

qInfo says:
exitCode in Slot 1
exit Status in Slot QProcess::NormalExit
1

jsulm

@qwe3 "but I have to write data to file and from file get data to QTextStream" - you do not need a file to use QTextStream, I still don't understand why you need a file... It would be way easier to get the output from the command without messing up with temp file.

QProcess proc;
QString cmdCommand = "cmd";
QStringList param;
param << "/c" << "net" << "use";
proc.start(cmdCommand, param);
proc.waitForFinished();
QTextStream stream(proc.readAllStandardOutput());

Does your current code write the file or not?

qwe3

@jsulm Ok, so the problem is that I can't use QProcess. I have to use winApi CreateProcess, which is a little different. And in this CreateProcess the new process will be have shell parent, so this is very strange. I know. That new process will be execute cmdCommand. I know that can be problem with ( waitForFinished, but at this moment is not a problem ). So I can't use readAllStandardOutput. I have to write data to File. This is only way. So now i would like know why this code with QTemporaryFile and QProcess doesn't work. Of course QProcess works when I use it with file which is on the Desktop or will be created.

I tested CreateProcess from WinApi and it works, but I have to use QTemporaryFile. So I started from QTemporaryFile and QProcess.

EDIT my last code which is here: there is no data on temporary File.

jsulm

@qwe3 I'm completely lost now: why do you think you can't use QProcess?
Did you actually try the code I provided?
net is writing to stdout as far as I know (maybe stderr, but that you also can read using QProcess), so using readAllStandardOutput() should give you output from net without any files.

qwe3

@jsulm Because my app is with administrator privileges. So when I do something like:
process->start("cmd /c net use Z: \192.168.24.12\folderName") I mapped disk to administator Files and I don't see it on myComputer. I read about it on other forum. Because cmd will be has admin privileges too. So I have to create Process with no admin privileges. And createProcess from winApi can do something like that.

Yes, when I use readAllStandardOutput and I don't use temporaryFile everything is ok. But I have to use temporaryFile.

EDIT and I want to execute "net use", which give me all drivers mapped to my account ( when I execute this cmd command with admin privileges I get all drivers mapped to admin ).

JonB

@qwe3
I too am lost, but why do you think a temporary file created in one process with certain privileges/in a certain location will be accessible/writeable by another process with different privileges? (I think that's what you're doing, you have shown various different code.)

qwe3

@JonB I can create file with createProcess and access to it ( for example read ) from my Main App with admin privileges. I check that. But I want only to use temporary File - no file which is on Desktop. I think the information about winapi and createProcess is not important. Now I only would like to create Temporary File, write to it some data using QProcess and qDebug() this data from file. But I don't want use readAllStandardOutput. Why? When I can do this -> write data to file and read it I can do the same with CreateProcess and QTemporaryFile. So please forgot about winapi :)

JonB

@qwe3
I never said anything about "winapi". It is you who say something about the sub-process is running with different permissions from the parent process which creates the file, that's all I'm talking about.

I think also you are running cmd /c something > tempfile. Does it help instead if you try https://doc.qt.io/qt-5/qprocess.html#setStandardOutputFile, so you don't have to do the redirection in the command?

Finally, instead of using QTemporaryFile, what happens if you (temporarily) try a fixed, non-temporary file path? To eliminate whether question has anything to do with QTemporaryFile.

qwe3

@JonB I would like to don't write any path to File and delete that file when it finished job. QTemporaryFile do exactly what I want - no Path and setAutoRemove.

J.Hilk

@qwe3 are you sure about the life time of your QTemporaryFile object ? because the file will be deleted when the object ist destroyed. Thats one of THE features QTemporaryFile has

https://doc.qt.io/qt-5/qtemporaryfile.html#details

and the file will subsequently be removed upon destruction of the QTemporaryFile object

qwe3

@J-Hilk
But in my code:

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QDebug>
MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    tmpFile = new QTemporaryFile;
    tmpFile->open();
    proc = new QProcess;
    tmpFile->close();
    connect(proc, SIGNAL(errorOccurred(QProcess::ProcessError )), this, SLOT(errorOccurredSlot(QProcess::ProcessError)));
    connect(proc, SIGNAL(finished(int , QProcess::ExitStatus )), this, SLOT(finishedSlot(int , QProcess::ExitStatus )));
    proc->start(R"(cmd /c "net use > )"+tmpFile->fileName()+R"(")");
    proc->waitForFinished();

    qInfo()<<proc->exitCode();

    qInfo()<<tmpFile->fileName();
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::errorOccurredSlot(QProcess::ProcessError error)
{
    qInfo()<<"error"<<error;
}

void MainWindow::finishedSlot(int exitCode, QProcess::ExitStatus exitStatus)
{
    qInfo()<<"exitCode in Slot"<<exitCode;
    qInfo()<<"exit Status in Slot"<<exitStatus;
}

I don't destroy temporary File, so I can go to Windows Explorer and open this file. When I open it, it really exists ( when I change one letter there is error "that file not exists" ). But temporary File is empty.

J.Hilk

@qwe3 And you say with File it works ? Than QTemprorayFile is the wrong approach here.

if you control both programs, than there are other better options to transfer information between those programs