Write to QProcess

[Max Fleischer]

I'm developing a UI with Qt Creator that controls an OPC Server.

Check Input Function OPC Server:

void runUserInterface()
    {
	// we have an endless loop waiting for a keyboard input
	bool end = false;
	_tprintf(_T("The server is running.\n"));
	usage();
 
	while(!end)
	{
		// variables for input purposes
 
		tstring input = _T("");
 
		cin >> input;
 
			if (input == _T("x") || input == _T("q") || input == _T("X") || input == _T("Q"))
			{
				// exit if one of the four exit characters is hit
				_tprintf(_T("Shutdown\n"));
				end = true;
			}
			if (input == _T("s"))
			{
				// exit if one of the four exit characters is hit
				_tprintf(_T("Shutdown\n"));
				end = true;
			}
	}
    }

void runUserInterface()
    {
	// we have an endless loop waiting for a keyboard input
	bool end = false;
	_tprintf(_T("The server is running.\n"));
	usage();

	while(!end)
	{
		// variables for input purposes

		tstring input = _T("");

		cin >> input;
		
			if (input == _T("x") || input == _T("q") || input == _T("X") || input == _T("Q"))
			{
				// exit if one of the four exit characters is hit
				_tprintf(_T("Shutdown\n"));
				end = true;
			}
			if (input == _T("s"))
			{
				// exit if one of the four exit characters is hit
				_tprintf(_T("Shutdown\n"));
				end = true;
			}
	}
    }

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When I run it in Visual Studio, it's working and the Server shuts down. When I write to the Process in Qt Creator, the UI stops working.

Source Code from UI

#include "control_window.h"
    #include "ui_control_window.h"
    #include "configuration_window.h"
 
    #include "configuration_window.cpp"
    #include <QProcess>
    #include <QWidget>
 
    #define CMD_EXIT "q"
 
    control_window::control_window(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::control_window)
    {
    ui->setupUi(this);
    }
 
    control_window::~control_window()
    {
    delete ui;
    }
 
    void control_window::on_control_window_Exit_clicked()
    {
    m_opc_ua_server->write(CMD_EXIT);
    m_opc_ua_server->waitForBytesWritten();
    }

#include "control_window.h"
    #include "ui_control_window.h"
    #include "configuration_window.h"

    #include "configuration_window.cpp"
    #include <QProcess>
    #include <QWidget>

    #define CMD_EXIT "q"

    control_window::control_window(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::control_window)
    {
    ui->setupUi(this);
    }

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

    void control_window::on_control_window_Exit_clicked()
    {
    m_opc_ua_server->write(CMD_EXIT);
    m_opc_ua_server->waitForBytesWritten();
    }

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The UI just crashes when on_control_window_Exit_clicked() is triggered, the OPC Server is still running though.
It also crashes when I use m_opc_ua_server->terminate();

I think the problem is in the UI, I made a small test program and the same error occurs.

test program:

#include "stdafx.h"
    #include <string>
    #include <iostream>
 
    class MyClass
    {
    public:
	MyClass();
	~MyClass();
	void checkinput();
 
    private:
 
    };
 
    MyClass::MyClass()
        {
        }
 
    MyClass::~MyClass()
    {
    }
 
    void MyClass::checkinput()
    {
    }
 
    string input = "";
 
    void checkinput()
    {
	cin >> input;
    }
 
    int main()
    {
	bool end = false;
	while (!end)
	{
		checkinput();
		if (input == "j")
		{
			end = true;
		}
	}
    }

#include "stdafx.h"
    #include <string>
    #include <iostream>

    class MyClass
    {
    public:
	MyClass();
	~MyClass();
	void checkinput();

    private:

    };

    MyClass::MyClass()
        {
        }

    MyClass::~MyClass()
    {
    }

    void MyClass::checkinput()
    {
    }

    string input = "";

    void checkinput()
    {
	cin >> input;
    }

    int main()
    {
	bool end = false;
	while (!end)
	{
		checkinput();
		if (input == "j")
		{
			end = true;
		}
	}
    }

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What's wrong?

[ChrisW67]

m_opc_ua_server has not been initialised anywhere in the code you show.

[Max Fleischer]

Do you mean that?

m_opc_ua_server = new QProcess(this);

That's in the previous window.

[Lesiok]

In header it is defined but nowhere is initialized - it has a random value.

[Max Fleischer]

Ok, thanks. That's the error, when I write to it in the window where it's started, the process reads it. But how can I initialize the process in the following windows?

[Lesiok]

You must pass a pointer to the window control_window - for example as a parameter to the control_window constructor.

[Max Fleischer]

How can I do that? Should i use an initialization list?

control window header:

#ifndef CONTROL_WINDOW_H
    #define CONTROL_WINDOW_H
 
    #include <QWidget>
    #include <QProcess>
 
    class QProcess;
 
    namespace Ui {
    class control_window;
    }
 
    class control_window : public QWidget
    {
        Q_OBJECT
 
    public:
        explicit control_window(QWidget *parent = 0);
        ~control_window();
 
        void sendExit();
 
    private slots:
        void on_control_window_Exit_clicked();
 
    private:
        Ui::control_window *ui;
 
        QProcess *m_opc_ua_server;
    };
 
    #endif // CONTROL_WINDOW_H

#ifndef CONTROL_WINDOW_H
    #define CONTROL_WINDOW_H

    #include <QWidget>
    #include <QProcess>

    class QProcess;

    namespace Ui {
    class control_window;
    }

    class control_window : public QWidget
    {
        Q_OBJECT

    public:
        explicit control_window(QWidget *parent = 0);
        ~control_window();

        void sendExit();

    private slots:
        void on_control_window_Exit_clicked();

    private:
        Ui::control_window *ui;

        QProcess *m_opc_ua_server;
    };

    #endif // CONTROL_WINDOW_H

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[Max Fleischer]

I've figured it out and wrote the answer in a more recent thread:

http://www.qtcentre.org/threads/6794...179#post298179