Call a script in parallel in Qt C++

Question

I am trying to run a script in parallel to my Qt program and am having trouble starting it as a separate process. Check out my attempts below and let me know what you see wrong.

The first attempt was just a system call:

system("python3 startprocess.py");

This works but it also stops the program while running it.

I then followed this guy https://forum.qt.io/topic/92205/writing-commands-to-linux-bash with no success. No errors, just no start of my script.

I am trying this after I saw the documentation and have the below code.

QProcess process;
process.start("python3 startprocess.py");
process.waitForStarted();

I am just wanting to start this script and have it run at the same time as my C++ code. Perhaps I am using the QProcess wrong?

UPDATE: It was a lot easier to use QThreading and the original system call.

Answer 1

I think the issue is that the QProcess doesn't have the file path and fails to find and start it! I suggest first to use the full file path! Also check the QProcess::setWorkingDirectory and QProcess::setProcessEnvironment that are useful to handle this case!

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Update

In order to prevent the QProcess to be killed while running and without freezing the GUI, you need to define it as a pointer, then connect the QProcess::finished event; in the slot, you can check the exit code and delete the sender using QObject::deleteLater method. Check both the Qt example and the QProcess::finished.

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Update 2

Try this code:

auto process = new QProcess(this);
connect(process, QOverload<int,QProcess::ExitStatus>::of(&QProcess::finished), 
[this](int exitCode, QProcess::ExitStatus exitStatus) 
{
    if (exitStatus == QProcess::ExitStatus::CrashExit 
        || exitCode != 0) {
        // Process error!
    } else {
        // Process OK!
    }
});
process->setWorkingDirectory("startprocess.py folder location");
process->start("python3 startprocess.py");
if (!process->waitForStarted(-1)) {
    // Failed to start process
    delete process;
}