[Qt-interest] newbie: application locks up

[john doe]

On Fri, May 1, 2009 at 1:12 PM, john doe <thebiggestbangtheory at gmail.com>wrote:

>
>
> On Fri, May 1, 2009 at 2:47 AM, chandrasekar wagmare <
> sekarwagmare at gmail.com> wrote:
>
>>
>> use this two signals in QProcess() :
>>  void readyReadStandardOutput();     //when a stdoutput is available
>>  void readyReadStandardError();         //when a stderror is available
>>
>> and use  QByteArray readAllStandardOutput(); and readAllStandardError() ;
>> to read the std output or error of the external process in a QString and
>> display it in the box;
>>
>>
> This is great! thanks a ton!
>
>
>>
>> ay 1, 2009 at 1:19 PM, john doe <thebiggestbangtheory at gmail.com> wrote:
>>
>>>
>>>
>>> On Fri, May 1, 2009 at 12:46 AM, chandrasekar wagmare <
>>> sekarwagmare at gmail.com> wrote:
>>>
>>>>
>>>> u have two ways, invoking an external program using QProcess()
>>>> and if u dont want the gui part freeze use QThread() .
>>>>
>>>
>>> awesome! I will look them up.. and since we are on the topic how can I
>>> set up a 2-way communication with the external program to display any error
>>> msgs in a text box or something?
>>>
>>> Thanks again
>>>
>>>
>>>> On Fri, May 1, 2009 at 1:08 PM, john doe <
>>>> thebiggestbangtheory at gmail.com> wrote:
>>>>
>>>>> Hello all,
>>>>>              Still relative newbie with Qt. I have made my first form
>>>>> containing combo buttons, lineedits and whatnot :-). I am facing a problem
>>>>> though regarding calling an external program from within the C++ Qt code.
>>>>>
>>>>> I have a ubuntu system and want to invoke a shell script which does
>>>>> some string manipulations on a large file. I used system() within the C++
>>>>> code to do it and it runs. The problem is that when I press a button to
>>>>> start the external program, if it takes 10 minutes to finish, the button
>>>>> seems to be depressed for this duraion. Basically, like waiting for the
>>>>> program to finish. How can I make the button not be depressed for this
>>>>> complete duration so that I can possibly start another instance of the
>>>>> external program by pressing a button on the main form.
>>>>>
>>>>> I am not an expert programmer, but I think this smells of asynchronous
>>>>> calls..right? Any insight would be greatly appreciated :-).
>>>>>
>>>>> I did try using a & at the end of the external program I am invoking
>>>>> but that does not help. Nothing runs. I am using kdesudo to start the
>>>>> external program as it requires certain privileges.
>>>>>
>>>>> Also I tried to use a progress bar with minimum and max set to 0 to
>>>>> continuosly work while the external program is running and it does not seem
>>>>> to work. Any pointers to threads/articles?
>>>>>
>>>>> Thanks in  advance.
>>>>>
>>>>> _______________________________________________
>>>>> Qt-interest mailing list
>>>>> Qt-interest at trolltech.com
>>>>> http://lists.trolltech.com/mailman/listinfo/qt-interest
>>>>>
>>>>>
>>>>
>>>>
>>>> --
>>>> WAGMARE
>>>>
>>>
>>>
>>
>>
>> --
>> WAGMARE
>>
>
> Thanks everyone for helping out. I used the suggestions to write up some
code..which unfortunately does not work.. its probably some easy thing that
I am not identifying!

I am using Qt 4.4.3, on Ubuntu 8.10 and am using QDevelop as an IDE. I have
3 files dialogimpl.h, min.cpp and dialogimpl.cpp. The code follows below.

dialogimpl.h
[code]

#ifndef DIALOGIMPL_H

#define DIALOGIMPL_H

//

#include <QDialog>

#include "ui_dialog.h"

//

class DialogImpl : public QDialog, public Ui::mygui

{

Q_OBJECT

public:

DialogImpl( QWidget * parent = 0, Qt::WFlags f = 0 );

public slots:

void getPathdir();

void getPathsisterfile();

void startjob();

void readstdoutput();

};

#endif
[/code]

main.cpp contains
[code]

#include <QApplication>

#include "dialogimpl.h"

//

int main(int argc, char ** argv)

{

QApplication app( argc, argv );

DialogImpl win;

win.show();

app.connect( &app, SIGNAL( lastWindowClosed() ), &app, SLOT( quit() ) );

return app.exec();

}

[/code]

and finally dialogimpl.cpp contains
[code]

#include <QtGui>

#include "dialogimpl.h"

#include <stdio.h>

#include <stdlib.h>

#include <iostream>

#include <fstream>

#include <QThread>

using namespace std;

//code still being tested

QObject *parent;

QString program;

QProcess *myProcess = new QProcess(parent);

QStringList arguments;

 //

DialogImpl::DialogImpl( QWidget * parent, Qt::WFlags f)

: QDialog(parent, f)

{

setupUi(this);

 // signals/slots mechanism in action

connect( startjobpushButton, SIGNAL( clicked() ), this, SLOT( startjob() )
);

connect( pushButton_browse_1, SIGNAL( clicked() ), this, SLOT( getPathdir()
) );

connect( pushButton_browse_2, SIGNAL( clicked() ), this, SLOT(
getPathsisterfile() ) );

connect(myProcess, SIGNAL(readyReadStandardOutput()), this,
SLOT(readstdoutput()));

}


//This function makes does something

void DialogImpl::startjob()

{

//declare vars

....

//make a config file

 QFile file("/home/temporary-file.txt");

QString line;

if ( file.open(QIODevice::WriteOnly) ) {

 // file opened successfully

// use a text stream

QTextStream out( &file );

out << "Target=" << Target << endl;

 // Close the file

file.close();

 //start the job

 program="echo";

arguments << "hello";

myProcess->start(program, arguments);

         //remove the file

file.remove();

}

else

{

//failed to open file

textEdit_output->insertPlainText("ERROR: Failed to create temporary file");

}

 }

 //This function allows for the user to

//read std output

void DialogImpl::readstdoutput()

{

QString output;

 output=myProcess->readAllStandardOutput();

textEdit_output->insertPlainText("ERROR: test msg to be displayed in text
box");

textEdit_output->append(output);

}

[/code]

What I want to do is when I click startjobpushbutton, a process should be
invoked, which does "echo hello" and I should be able to see "hello" in the
textEdit_ouput text box. Currently, when I click the button nothing happens.
Can someone please provide a little insight.

Thanks in advance.
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