@thamht4190 I would have thought the most likely reason for the "crash" is that pid->hProcess is "not valid" at the instant GetExitCodeProcess() is called. Again, only a guess, but: in your onReadyReadStandardOutput() you terminate the process. Bearing in mind that is a slot called while the process is still very much active, I wonder what state things might be in internally when that returns. I would start by commenting out your "process termination" stuff and see where that gets you?

@jsulm I did :-) but I have no more information... Anyway I will stop using the QProcess class to reccord video with my webcam, it seems too tricky, instead I think I will use a library like LibVLC to do it...

@JonB Thank you for correct direction. I will modify my code and use it finished Signal for updating dialog box.

@JonB Thanks! That saved me a good deal of troubleshooting. It turned out the problem was a hard path to a file inside the C program which caused it to run correctly when invoked from it's native directory, but caused a segfault when called by Qt since the paths were different. The problem is completely fixed now.

Hi, Thank you for your reply. I totally changed my implementation using the signal and slots. Thank you so much again.

@BitFlipper b) I tried that already with no luck Then you did not try right! There is an example of just what you need at the link I posted. The outline of this approach would be: QProcess ddProcess, md5sumProcess; ddProcess.setStandardOutputProcess(&md5sumProcess); ddProcess.start("sudo dd if=/dev/sda2 of=/dev/sdb2 bs=4096 conv=noerror"); md5sumProcess.start("md5sum"); md5sumProcess.waitForFinished(); However, it's probably more suitable for you to issue the whole lot as a single string passed to /bin/sh or /bin/bash with the -c argument, and let it figure the | for you., as per my example earlier. So my command changes in this function, should I build a custom string every time and pass it in as one statement? Yes. I always practice in terminal first For this purpose make yourself use /bin/sh -c "sudo dd ... | md5sum" as that is what you will need. Be careful if anything in your command requires its own quoting (your current example does not), as the whole command itself is now inside quotes. As I wrote earlier, your md5sum is not going to see the contents from the dd. Your example does not lend itself to checksumming as it uses a single dd if=... of=... which does the input & output in one go. What you want is for the output from the dd to go both to the output file and to md5sum. Here are two possibilities for you to play with: sudo dd if=/dev/sda2 bs=4096 conv=noerror | sudo tee /dev/sdb2 | md5sum sudo dd if=/dev/sda2 bs=4096 conv=noerror | tee >(md5sum 1>&2) | sudo dd of=/dev/sdb2 bs=4096 In the first case we tee the output off to /dev/sdb2 as well as letting it through to md5sum. Simpl-ish, but you lose the ability to specify the bs= for the output to /dev/sdb2. I don't know if that matters to you. In the second case you use "shell magic" (you'll probably have to use /bin/bash not /bin/sh, I think) to send tee's output to md5sum process as well as passing it onto a second dd to do the output. I have made it so md5sum's output goes to standard error instead of standard output. Finally: is all this dd and checksum stuff worth it? Probably not. Have a read of, say, https://unix.stackexchange.com/a/45854/104736 for alternative suggestions.

Hi, I have found something that works but that is not really "clean" in my opinion : QString password = "yourRootPassword"; //could be asked with QInputDialog::getText(...) QString cmd = QString("sudo -S kextunload -b %1 > /dev/null").arg(driverName); FILE *pipe = popen(cmd.toStdString().c_str(), "w"); if(pipe != nullptr) { fprintf(pipe, "%s\n", password.toStdString().c_str()); if (ferror(pipe)) { qDebug() << "Failed to write to pipe"; } else { qDebug() << "Written to pipe"; } } else { qDebug() << "Failed to open pipe"; } qDebug() << "Pipe returned : " << pclose(pipe); I don't know how to use the Apple method linked by SGaist...

thanks !! . I will look into both of them

You might have modified PATH in your terminal session only for example. Or you may have modified PATH in the Run part of the Project panel.

@Thanos thanks for your feedback. So please mark this topic as SOLVED now.

Hi and welcome to devnet, You should take a look at the various IPC options provided by Qt.

IIRC, you have QTest;:wait for that kind of stuff.

@Naim Use http://doc.qt.io/qt-5/qprocess.html#readyReadStandardOutput and http://doc.qt.io/qt-5/qprocess.html#readyReadStandardError to get notifications each time the process writes something to stdout or stderr and read it using http://doc.qt.io/qt-5/qprocess.html#readAllStandardOutput and http://doc.qt.io/qt-5/qprocess.html#readAllStandardError. Do not call waitForFinished, just make sure your proc does not go out of scope (make it class member).

@gizalp Why do you think python (or anything else) is going to open any terminal window? And what OS are you on anyway? For QProcess:setProgram you should have process.setProgram("python");, only. But in this case I think it's getting overridden by your process.start("python test.py"); so it doesn't matter, but it's wrong. If you want to grab a sub-process's output, you have to handle QProcess::readyReadStandardOutput(), and in there something like QByteArray QProcess::readAllStandardOutput(), if that's what you mean by "How can I get the 'Hello' output?". How this relates to Trying to implement thumbnail list I have no idea....

@gizalp said in Qt Signal Slot: @mostefa Thanks, that fixed my problem! You are welcome =)

@kshegunov I see, now i understand. Thank you for your help and for your patience.

You can't read from a finished program. you have to connect to readyRead(); replace process->start(cmd,comandlist,QIODevice::ReadOnly ); if (!process->waitForFinished()) { lstr = QString(); } else { lstr = QString(process->readAll().constData()); } return lstr; with QObject::connect(process,&QProcess::readyReadStandardOutput,[&lstr,process]()->void{lstr.append(QString::fromLatin1(process->readAllStandardOutput()));}); process->start(cmd,comandlist,QIODevice::ReadOnly ); if (process->waitForFinished()) return lstr; return QString();

@SGaist Good one! Though I had to use the C++11 version since C++14 is still in Debian Sid. // C++11 connect(process, QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished), this, &MainWindow::close); For those who want to know, this is the C++14-version: // C++14 connect(process, qOverload<int, QProcess::ExitStatus>(&QProcess::finished), this, &MainWindow::close); Since the actual problem of this thread is solved, I will mark this thread as solved tomorrow. In the mean time comments on the above code can be made.

Well, actually it does work! But if bash is not running interactively, it won't read the .bashrc where the shell-variables are stored. So I did the following: sh.start("bash -i"); // the -i tell bash to run interactively if(sh.waitForStarted()) sh.write("printenv JAVA_HOME"); // or sh.write("echo $JAVA_HOME") sh.closeWriteChannel(); In case you were wondering, I connected the QProcess::finished signal to a slot where the QProcess::readAllStandardOutput is put in a QPlainTextEdit. The QProcess::processEnvironment is not updated however. Even if I try to export JAVA_HOME with sh.write("export JAVA_HOME"). While that is not what I expected, I now can find the local shell-variables. So I will mark this problem as solved. Thanks!

Can you share the QProcess code you have written to execute the script ?

Original SO thread

@VRonin said in Send arrow keys via QProcess in any platform: @Mark81 Then do you really need Qt? there are already mature tools to do those kind of things, for windows: http://ahkscript.org/ and for linux: http://www.semicomplete.com/projects/xdotool/ I don't need Qt for this. But I have a quite large application that does a lot of things. One of those, is to launch external applications and send them keystrokes as you would type in front of a keyboard.

Thanks! Marking solved.

How can I fix this problem?

Writing a newline separately works, as suggested by micland. Thanks guys!

We can do something. You need to use event filters along with process communication. Can you paste the which you have tried ? That will help us quickly get you the solution.

Do you have any logging going on that would allow you to check whether your nodejs server does something ?

One thing to add to @kshegunov, terminating these applications ungracefully may have side effects on the stability of your system.

@marlenet15 @Paul-Colby said: Of course you should always be careful with sudoers, but even more so when using wildcards. That's good advice and only to throw my 2 cents in: Allowing users to change system-wide settings somehow defeats the whole point of having users in the first place. What happens if one user changes the timezone, but another is not happy with that and changes it back? These are system changes we're talking about, so that's one good reason for actually having a super user that manages them ...

Hi, Thanks for your response. The whole body of code is proprietary so I'm not sure I can share it in a public forum. However I can make a note that it used to work fine a month ago and after that no changes occurred to this code and no qt libraries were replaced, so the issue is like to be caused by hardware malfunction. Thanks again ))

Glad you found out and thanks for sharing ! Since you have it working now, please mark the thread as solved using the "Topic Tool" button so that other forum users may know a solution has been found :)

Basically, it's not a part of Qt that you access directly. It's part of the platform plugins that abstracts away the differences between the various supported OSs. The best I can recommend is to contact the KDE folks about how the startup notification is handled by them.

@SGaist Thanks, it helped!

I realized that the command was wrong and wasn't recognizing my partitions.