executing cmd.exe with some console application

[Robert M.]

I am using C++ i Qt5.
I want to execute (from my Qt5 application) some console application with arguments but I want to have cmd.exe window visible with program's produced output.
I tried in my Qt5 application:

std::string terminal = exec_system(L"echo %windir%") +
"\system32\cmd.exe";
QProcess *process = new QProcess();
QString exec = QString::fromStdString(terminal);
QStringList params;
params << "/C";
for (std::string s : explode(std::string(" "), command)) {
params << s.c_str();
}
process->start(exec, params);
process->waitForFinished();
delete process;

Unfortunately cmd.exe window is not shown. I see hourglass for some time, but no cmd.exe window.
How to do it?

[jsulm]

@Robert-M said in executing cmd.exe with some console application:

std::string terminal = exec_system(L"echo %windir%") +
"\system32\cmd.exe";

"cmd.exe" should be enough.
What exactly does exec contain?
You also should add error handling (https://doc.qt.io/qt-5/qprocess.html#errorOccurred)
No need to allocate process on the stack if you anyway wait for it to finish.

[Robert M.]

QProcess process;
QString cmd = QString::fromStdString("cmd.exe");
QStringList params;
params << "/C" << "pause";
process.start(cmd, params);

This code does not display console window. Why? How to make it correct?
I use Win10.

[JonB]

@Robert-M said in executing cmd.exe with some console application:

This code does not display console window. Why?

What about it makes you think it should display any kind of console window? It will not.

How to make it correct?

I believe (I am not a Windows Qt user) you must do one of:

• In .pro add CONFIG += console. But that will display a console the whole time, and I don't think is compatible with GUI application.

• You probably want to look into the Windows AllocConsole() function.

• IIRC, use Windows CreateProcess... calls, instead of QProcess, which do allow console creation.

• Find a "terminal" which will execute your command. For example under Linux you could run it by invoking xterm -e ...; I don't know about Windows.

[Robert M.]

I know how to do it in Linux, my solution works fine in Linux. I do not know how to do it in Windows.

[JonB]

@Robert-M
What is your solution which works in Linux then?

I suggested the ways you can do it in Windows. Sorry if that's not what you wanted to hear or if Windows/cmd does not work the way you would like it to.

[JonB]

@Robert-M
There may be a way to get Qt's QProcess to control the arguments being passed to Windows CreateProcess, which I said you will need to do in order to have it create a new console for the sub-process. Have a look at void QProcess::setCreateProcessArgumentsModifier(QProcess::CreateProcessArgumentModifier modifier) and the discussion at typedef QProcess::CreateProcessArgumentModifier. I have not tried it, but in the sample code there I see

args->flags |= CREATE_NEW_CONSOLE;

Try that, and then try it for your pause command. You may, or may not, need the cmd /k it shows there rather than cmd /c, depending what you want to happen about the console when your command finishes.

Note that what you will want/expect to happen to the console after your command executes will depend on what command you are issuing. Likely not the same for echo versus pause.

[Robert M.]

I tried (according to Qt documentation):

QProcess process;
process.setCreateProcessArgumentsModifier([] (QProcess::CreateProcessArguments *args)
   {
       args->flags |= CREATE_NEW_CONSOLE;
       args->startupInfo->dwFlags &= ~STARTF_USESTDHANDLES;
       args->startupInfo->dwFlags |= STARTF_USEFILLATTRIBUTE;
       args->startupInfo->dwFillAttribute = BACKGROUND_BLUE | FOREGROUND_RED
                                          | FOREGROUND_INTENSITY;
   });
process.start("C:\\Windows\\System32\\cmd.exe", QStringList() << "/c" << "pause");

but it does not display console window. Using /k instead of /c does not help.

[Robert M.]

In Linux I call process->start(...) with xterm.

[VRonin]

Did you try using startDetached instead of start?

[Robert M.]

You are great! Thanks a lot!

process.setProgram("C:\\Windows\\System32\\cmd.exe");
process.setArguments({"/k", "pause"});
qint64 pid;
process.startDetached(&pid);

displays console with pause text.

[JonB]

@VRonin said in executing cmd.exe with some console application:

Did you try using startDetached instead of start?

Interesting. But why does that allow the new console where start does not? :)

[VRonin]

start is designed explicitly to avoid popping new consoles up, see the comment block in https://code.woboq.org/qt5/qtbase/src/corelib/io/qprocess_win.cpp.html#550

we [...] do not want console tools launched from a GUI app to create new console windows (behavior consistent with UNIX).

[JonB]

@VRonin said in executing cmd.exe with some console application:

see the comment block in https://code.woboq.org/qt5/qtbase/src/corelib/io/qprocess_win.cpp.html#550

// However, we also do not want console tools launched from a GUI app to
// create new console windows (behavior consistent with UNIX).
DWORD dwCreationFlags = (GetConsoleWindow() ? 0 : CREATE_NO_WINDOW);

Well no wonder then :) But we don't get told this is a difference from startDetached() :) I will try to remember this for the future.

P.S.
Isn't just lovely to see UNIX written? :)

[JonB]

@VRonin said in executing cmd.exe with some console application:

start is designed explicitly to avoid popping new consoles u

Not tested, but can't you change this in the same way in your setCreateProcessArgumentsModifier() anyway, just add the first line to whatever you want:

args->flags &= ~CREATE_NO_WINDOW;  // switch that *off*
args->flags |= CREATE_NEW_CONSOLE;
...

?

If this works for start() like the OP says it apparently is working for startDetached() the advantage is you can still wait for sub-process completion, if desired.

[VRonin]

Indeed you can!

[Robert M.]

I have one problem in Linux. I invoke xterm with dirtyphp.sh script:

    QProcess process;
    QString exec = QString::fromStdString(terminal);
    QStringList params;
    params << "-hold" << "-e"; 
    bool p0 = true;
    for (std::string s : explode(std::string(" "), dirtyphp_command)) {
        if (p0) {
            std::string s0 = str_replace("'", "", s) + ".sh";
            params << s0.c_str();
            p0 = false;
        } else {
            params << str_replace("'", "", s).c_str();
        }
    }
    process.start(exec, params);
    process.waitForFinished();

In dirtyphp.sh script I am waiting for CTRL+C at the end:

d=`dirname $0`
if [ "$d" = "" ]
then
	d="."
fi
$d/dirtyphp $@
echo 'Hit CTRL+C';
while true 
do
	sleep 1
done 

The problem is that xterm window is closed automatically without waiting for CTRL+C and the user cannot browse output produced by program dirtyphp in xterm window. I do not understand why - the loop and the end of dirtyphp.sh script should be infinite.

[JonB]

@Robert-M
If you think it's even executing that script and getting as far as the while true loop (goodness knows), put some debugging into the loop, like an echo or a read.

Or maybe put a set -x at the start of the script so you can see what is going on?

[Robert M.]

I changed the loop to the following:
while true
do
echo -n _
done
I see no underscores in xterm window.
Qt reports:
QProcess: Destroyed while process ("xterm") is still running.
I modified waitForFinish call:
process.waitForFinish(-1);
and now I can see underscores.
Problem solved.

[JonB]

@Robert-M
bool QProcess::waitForFinished(int msecs = 30000) means that waitForFinished() only waits up to 30 seconds, and then your QProcess process; goes out of scope and causes the error. If your sub-process takes longer that is why you wanted waitForFinished(-1).