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c++qtqprocessqtcoreqfile

How to execute command like "qmake -v > 1.txt" from a specific folder with QProcess?

I have a path to a folder and a command to execute from that folder. It's an arbitrary complex command. For ex.: qmake -v > 1.txt.

I figure I need to run a shell (cmd.exe because I'm on Windows atm.), and execute the command there:

QProcess::startDetached("cmd.exe", QString("qmake -v > 1.txt").split(' ',

QString::SkipEmptyParts), "C:/folder/");

But it doesn't work. It does launch a console window (cmd.exe) at the specified path, but doesn't execute the command. Then I've tried:

QProcess::startDetached("cmd.exe", QStringList() << "start" << QString("qmake -v > 1.txt").split(' ', QString::SkipEmptyParts), "C:/folder/");

Also no luck. And finally, just to test if I'm going anywhere with this at all:

QProcess::startDetached("qmake.exe", QString("-r -tp vc").split(' ', QString::SkipEmptyParts), "C:/folder_containing_qt_project/");

A console window appears for a brief moment, but project is not generated.

What am I doing wrong, and how can I achieve what I want with QProcess (I don't mind using WinAPI if there's no other way, but strongly prefer to use the same code on Linux / Mac OS X / Windows)?

It might be worth noting that in another method of the same app I have no problem executing notepad.exe <path to a text file> with startDetached.

Solution

  • I think you are looking for this method:

    void QProcess::setStandardOutputFile(const QString & fileName, OpenMode mode = Truncate)

    You would be using it then like this:

    QProcess myProcess;
myProcess.setStandardOutputFile("1.txt");
myProcess.start("qmake -v");
myProcess.waitForFinished();

    You could also read the output into the application and write that out with QFile. This may get you going into that direction:

    QByteArray QProcess::readAllStandardOutput()

    Regardless of the current read channel, this function returns all data available from the standard output of the process as a QByteArray.

    Therefore, you could write something like this, but it is a bit more complicated, and potentially memory-hungry, so it is just for demonstratation purposes without chunk read and write.

    QProcess myProcess;
myProcess.start("qmake -v");
myProcess.waitForFinished();
QFile file("1.txt");
file.open(QIODevice::WriteOnly);
file.write(myProcess.readAllStandardOutput());
file.close();

    Disclaimer: I intentionally did not write error checking to keep it simple.