Qt startDetached fails under Qt 5.15.2 - c++

Question

I'm updating some old Qt 5.6 code to Qt 5.15.2
The Qt C++ code below opens a dos prompt, the runs a bat file, staying open when done.
cstring = "cmd /k " +QDir::currentPath()+"/cpath.bat";
QProcess::startDetached(cstring);
This code works fine under 5.6, does nothing under 5.15.2
How do I fix this for Qt 5.15.2?

Answer 1

You need to split the command to program and arguments. See https://doc.qt.io/qt-5/qprocess.html#startDetached-1
In your case it should be
QProcess::startDetached("cmd", {"/k", QDir::currentPath() + "/cpath.bat"});
The advantage is that now you do not need to worry for example about enclosing paths containing spaces in quotes. Consider if your current path would be "C:\my path". Then your version from Qt 5.6 would not work. While the version I presented in this answer will work out of the box. I guess it was exactly this reason that the old overload was prone to this kind of bugs that Qt decided to remove it and use only the new overload.

Answer 2

Ok, with my previous answer I though that the problem was with the way you are passing the arguments. But as it seems the problem is with showing the terminal... Since I am doing the same in one of my projects (HiFile file manager), I had a look how I am doing it. So here it is.
class DetachableProcess : public QProcess
{
public:
explicit DetachableProcess(QObject *parent = nullptr) : QProcess(parent)
{
}
bool detach()
{
if (!waitForStarted())
{
return false;
}
setProcessState(QProcess::NotRunning);
return true;
}
};
And then use it like this:
DetachableProcess process;
process.setCreateProcessArgumentsModifier( // this probably did the trick you need
[](QProcess::CreateProcessArguments *args)
{
args->flags |= CREATE_NEW_CONSOLE;
args->startupInfo->dwFlags &=~ STARTF_USESTDHANDLES;
});
process.start("cmd", {"/k", QDir::currentPath() + "/cpath.bat"}); // here are your params...
process.detach();
I am afraid I cannot give more explanation why this complicated method works, I do not know it. And I do not know why it was changed in Qt.
I hope it will work for you. It works for me in Qt 6.2.4, which I am currently using.