QProcess not working.

[KroMignon]

@SPlatten said in QProcess not working.:

yes, it didn't originally, I add those later just to see if it made any difference.

I don't really know what is the purpose of this, I guess you have to get SQL statements from you DB.

My way to achieve it would be:

• start mysqldump with QProcess
• wait until QProcess / mysqldump finished
• read QProcess output (cf. QProcess::readAll()) ==> no need of redirection at all

And last remark:
you have to do connection before starting process, to be sure not to loose state changes ;)

[SPlatten]

@KroMignon I don't follow you, if I copy the command line and arguments to a command prompt it works, the arguments are everything it needs for mysqldump to connect and export the database.

[JonB]

@SPlatten said in QProcess not working.:

@JonB , where are you getting process and exec from?

It's an example of QProcess::exec(). Actually that's static. Exactly the same principle if you want to use pobjProcess->start();. It's the argument passing I'm trying to tell you about.

if I copy the command line and arguments to a command prompt it works,

Yes, as I said this will (only) work from cmd.

                          << QString(">")

                          << strFilename;

As I said, this won't work for mysqldump run as an executable. It will only work via cmd /c .... Up to you whether you believe me :)

[KroMignon]

@SPlatten said in QProcess not working.:

I don't follow you, if I copy the command line and arguments to a command prompt it works, the arguments are everything it needs for mysqldump to connect and export the database.

With QProcess, you don't start the process from a shell / command prompt, that is the difference here.
Try this:

auto proc = new QProcess;
QObject::connect(proc, &QProcess::stateChanged,
                    [proc](QProcess::ProcessState newState)
{
    qDebug() << "new state is " <<  newState;
    if(newState == QProcess::NotRunning)
    {
        QString output(proc->readAll());
        qDebug() << "Output is" << output;
        proc->delateLater();
    }
});
proc->setWorkingDirectory(strDBinstFolder);
proc->start(strApp,slstArguments );

EDIT: do NOT add redirection in slstArguments !!!

EDIT BIS:

QStringList slstArguments;
slstArguments << (QString(DataSets::mscszOptionHost) + Trainer::strHost())
                              << (QString(DataSets::mscszOptionUser) + Trainer::strUser())
                              << (QString(DataSets::mscszOptionPassword) + Trainer::strPassword())
                              << (Trainer::strDatabase());

==> I suppose that DataSets::mscszOptionHost contains --host=

[SPlatten]

@JonB , not in Qt 5.9.2 it ins't, execute ?

[JonB]

@SPlatten
int QProcess::execute(const QString &program, const QStringList &arguments) [static]. So it's execute. It was introduced into some Qt. I don't know about 5.9.2.

As I said, forget I ever wrote exec or execute. The same argument processing applies to QProcess::start. You keep passing > argument, and I've explained this won't work.

[SPlatten]

@KroMignon , I've tried this:

QString strApp(DataSets::mscszMariaDBdumpApp);
QStringList slstArguments;
slstArguments << ("\"" + strDBinstFolder + strApp + "\"")
              << (QString(DataSets::mscszOptionHost) + Trainer::strHost())
              << (QString(DataSets::mscszOptionUser) + Trainer::strUser())
              << (QString(DataSets::mscszOptionPassword) + Trainer::strPassword())
              << (Trainer::strDatabase())
              << QString(">")
              << strFilename;
pobjProcess->setWorkingDirectory(strDBinstFolder);
pobjProcess->start(strApp, slstArguments);
QObject::connect(pobjProcess, &QProcess::errorOccurred,
    [this](QProcess::ProcessError err) {
qDebug() << "Error: " << err;
});
QObject::connect(pobjProcess, &QProcess::stateChanged,
    [pobjProcess](QProcess::ProcessState newState)  {
        const qint64 cint64PID(pobjProcess->processId());
        if ( newState == QProcess::NotRunning )  {
        }  else if ( newState == QProcess::Running && cint64PID > 0 )  {
        }
qDebug() << "PID: " << cint64PID << ", newState: " << newState;
});

[jsulm]

@SPlatten Did you notice "EDIT: do NOT add redirection in slstArguments !!!" in @KroMignon post?
Why do you need redirection to a file if you can simply read the stdout from the process as @KroMignon already suggested?

[KroMignon]

@SPlatten This don't make sense to me:

• Why do you add application into argument list?
• Why to you redirect it to a file and not directly read it for QProcess stream?

[SPlatten]

@jsulm The purpose of this is to provide an export / backup facility of the database to an SQL file.

[jsulm]

@SPlatten You can still write the stdout from the process to a file...

[SPlatten]

@KroMignon , as I said earlier I've tried numerous things, thats just one of variant.

[jsulm]

@SPlatten Also, as @JonB already wrote: you can't use redirection without a shell. Redirection is a feature of a shell (cmd.exe on Windows). So, you will need to execute cmd.exe as executable and pass everything else as parameters.

[SPlatten]

@JonB , just tried:

QProcess::execute(strApp);

strApp contains:

/c "C:/Program Files (x86)/MariaDB 10.5/bin/mysqldump" --host=localhost --user=trainer --password=CobhamAC training > C:/Users/simon.platten/Documents/TrainerS1D5.sql

Still not working.

[SPlatten]

@KroMignon , yes it does, I'll try without the application which is where I started.

[jsulm]

@SPlatten said in QProcess not working.:

QProcess::execute(strApp);

First parameter is the executable ("cmd.exe" in your case), second is a list of parameters...

[JonB]

@SPlatten
No, that is not what I said at all. Look at the example. The program needs to be cmd.exe. The arguments need to be first /c and second your whole command line (as a single argument; for cmd it doesn't seem to matter if you pass it as one string as I showed, or I think it will accept each argument separately). I showed you earlier an example of what you need.

[SPlatten]

@JonB , ok, having prefixed with cmd.exe it now works. Thank you, thank you everyone.

[JonB]

@SPlatten
Having said that. If the only purpose of having to go via cmd /c is to handle the redirection of output via >, I would handle that back in QProcess (I think others have suggested this) and then you won't need to go via cmd, which has its disadvantages.

[SPlatten]

@JonB I will investigate now.