Question

I am just trying to create a file with QProcess by the following source code:

void Processmethod()
{

    QDialog *ProcessMessage = new QDialog;      
    Ui::DialogProcessMessage Dialog;            
    Dialog.setupUi(ProcessMessage);             
    ProcessMessage->setModal(true);
    ProcessMessage->setAttribute(Qt::WA_DeleteOnClose); 
    ProcessMessage->show();

    processmethodONE(); 
} 

void processmethodONE()
{
    QString ProcessCommand = "w8 " + blablubli";            

    Prozess.setWorkingDirectory(Path);         //QProcess "Prozess" is globaly defined  
    Prozess.setStandardOutputFile(Path);       //in my class
    Prozess.start(ProcessCommand);

    QProcess::ExitStatus Status = Prozess.exitStatus(); 

    if (Status == 0)
    {
        std::cout << "File created!" << std::endl;
    }
}

This process creates out of another file which is located in the QString “Path” a new file, let me call it “PROFILE” (PRO for Problem :). The Profile also is created, but is never completed, I guess not even 50% of the file are completed.
Just when using

while(!Prozess.waitForFinished())
      {
       qApp->processEvents();
       std::cerr << "Process Create PROFile running " << std::endl;
      }

the file is written completely.
Furthermore I tried to use the QProcess finished(int) Signal to start another method and deleted the while loop (which freezes the whole GUI). I declared it in the constructor with:

connect(&Prozess, SIGNAL(finished(int)), this, (SLOT(processmethodTWO())));

But I guess this could not work because the first process isn’t finished completely. Where is the problem?

Answer 1

There is no warranty that right after Prozess.start(ProcessCommand); process will be finished, so calling “Prozess.exitStatus();” right after it will give you “false positive”. You certainly will have to wait until process is finished. You may either do it with with while loop, that you suggested or with QEventLoop

// ...
Prozess.setStandardOutputFile(Path);       //in my class
QEventLoop loop;
connect(&Prozess, SIGNAL(error(QProcess::ProcessError)), &loop, SLOT(quit()));
connect(&Prozess, SIGNAL(finished(int, QProcess::ExitStatus)), &loop, SLOT(quit()));
Prozess.start();
loop.exec();
// Now your process status should be valid:
QProcess::ExitStatus Status = Prozess.exitStatus();