QProcess::startDetached() doesn't work on self-written programs

[JonB]

@Qt_Bob
If output shows running and then not running a bit later maybe it has run to conclusion successfully with no output? How do we know what program you run and what it's supposed to do or how you know it is not working right?

Let's be 100% clear: you must be using start() here, do not even try to use startDetached(). If you cannot get that to work something is wrong.

Your code above should either be in readyRead.../finished/errorOccurred/stateChanged slots, or for the purpose of your test you can just go:

process.start(...);
qDebug() << process.waitForFinished();

followed by your code. Find out why your 2 programs "do not work".

[Qt_Bob]

@JonB @Christian-Ehrlicher

Ok, I hope this is ok.
At least it's compiling:

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QPushButton>
#include <QGridLayout>
#include <QProcess>
#include <QTextBrowser>
#include <QByteArray>
#include <QDebug>
#include <QTimer>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

private:
    Ui::MainWindow *ui;
    QProcess *process;

private slots:
    void open_program();
    void ausgabe();
};
#endif // MAINWINDOW_H

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    QPushButton *but_open = new QPushButton("Open");
    QGridLayout *layout = new QGridLayout();
    layout->addWidget(but_open, 0, 0);
    ui->centralwidget->setLayout(layout);
    connect(but_open,SIGNAL(clicked()),this,SLOT(open_program()));
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::open_program()
{
    MainWindow::process = new QProcess();
    QString pfad = "I:\\FabTech\\Anlagen-Dokumentation\\85 TEOS 200 mm\\Teos-Trapping\\TEOS-Überwachung\\TEOS-Abscheidungs-Programm\\TEOS_Abscheidung.exe";
    process->start(pfad);
    connect(MainWindow::process,&QProcess::stateChanged,this,MainWindow::ausgabe);
    connect(MainWindow::process,&QProcess::errorOccurred,this,MainWindow::ausgabe);
}

void MainWindow::ausgabe()
{
    qDebug() << MainWindow::process->readAllStandardError();
    qDebug() << MainWindow::process->readAllStandardOutput();
    qDebug() << MainWindow::process->error();
    qDebug() << MainWindow::process->state();
}

No changes to main.cpp

Only output I got:
""
""
QProcess::UnknownError
QProcess::NotRunning

mhhh... So in the next step I build and deploy the other programs again.
They are a bit complex.
I have a double-chained list in which data is read from a database and output in a text window.
The user can then enter all the data for a physical process in some QSpinBoxes, QLineEdits and so on and these are added to the database. Or the database can be searched for specific entries and so on. In addition, the open database can be archived under a specific name and archived databases can be opened, etc.
In any case, the program should remain open and wait for user input.

I can open multiple instances of the programs I want to open with my new program from Windows and never had errors or crashes (even while the new program is running). Just open it from the new program doesn't work.

[Christian Ehrlicher]

Then please try to start the not working program from a plain command line. Maybe some dlls are missing so it can not be started.

[Qt_Bob]

@Christian-Ehrlicher
It opens normally when I execute it from cmd. So that doesn't seem to be the problem?!

[Christian Ehrlicher]

@Qt_Bob Make sure the PATH env var is the same. You can get it from QProcess::systemEnvironment() and on the command line with 'set PATH'

[Qt_Bob]

@Christian-Ehrlicher
That could be it, I was editing the PATH env var to set up QwtPlot last week.
If I get the list from QProcess::systemEnvironment() it shows all the content in PATH. What should I look out for? The QT folder and MinGW and so on are set up correctly in any case. I spent a few hours on this to get QwtPlot run and make sure everything there is correct (I wanted to use python first for my new project,...). Should the PATH env var also contain something about the two programs?

Edit:
Ok I figured it out. I let it print both QProcess::systemEnvironment() and they are the same.

[JonB]

@Qt_Bob
Make sure your sub-programs do not care what the current directory is when run.

Put a qDebug() << "Hi there"; as first statement in sub-program, do you read that back successfully?

Make sub-program non-Qt, just plain Hello World, does that work?

[Qt_Bob]

@JonB
I have made a note of this next step in my diary and will carry it out as soon as possible and report back here. However, I will probably not be able to reply until 4 December. I'm sorry, I opened this topic at an inopportune time. One of the successfully tested programmes was pure C# without Qt and it worked. The other programmes were also developed in-house (Visual Basic, Pascal, ...). Apparently only the Qt programmes cause problems, but I will test this again with a "Hello World" programme with and without Qt.
Many thanks for the help.

[Christian Ehrlicher]

@Qt_Bob said in QProcess::startDetached() doesn't work on self-written programs:

Apparently only the Qt programmes cause problems

This sounds like a deployment issue.

[Qt_Bob]

@Christian-Ehrlicher, @JonB
I deployed the two programs again and had the same problem as before. Then I went through all the deployed .dll's and there were some missing. I copied them inside the folder manually and now it works.
So the problem was windeployqt or some missing windeployqt-commands while deploying.
Thank you again, I'll close this topic now.