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# Starting processes with IO redirection

This example shows you how to start other processes with Qt and how IO redirection is done. The example tries to start the uic (a tool that comes with the Qt Designer) on a certain ui file and displays the output of the command.

Implementation (process.cpp):

    /****************************************************************************
    ** $Id: qt/process.cpp   3.3.5   edited Aug 31 12:13 $
    **
    ** Copyright (C) 1992-2005 Trolltech AS.  All rights reserved.
    **
    ** This file is part of an example program for Qt.  This example
    ** program may be used, distributed and modified without limitation.
    **
    *****************************************************************************/

    #include <qobject.h>
    #include <qprocess.h>
    #include <qvbox.h>
    #include <qtextview.h>
    #include <qpushbutton.h>
    #include <qapplication.h>
    #include <qmessagebox.h>

    #include <stdlib.h>

    class UicManager : public QVBox
    {
        Q_OBJECT

    public:
        UicManager();
        ~UicManager() {}

    public slots:
        void readFromStdout();
        void scrollToTop();

    private:
        QProcess *proc;
        QTextView *output;
        QPushButton *quitButton;
    };

    UicManager::UicManager()
    {
        // Layout
        output = new QTextView( this );
        quitButton = new QPushButton( tr("Quit"), this );
        connect( quitButton, SIGNAL(clicked()),
                qApp, SLOT(quit()) );
        resize( 500, 500 );

        // QProcess related code
        proc = new QProcess( this );

        // Set up the command and arguments.
        // On the command line you would do:
        //   uic -tr i18n "small_dialog.ui"
        proc->addArgument( "uic" );
        proc->addArgument( "-tr" );
        proc->addArgument( "i18n" );
        proc->addArgument( "small_dialog.ui" );

        connect( proc, SIGNAL(readyReadStdout()),
                this, SLOT(readFromStdout()) );
        connect( proc, SIGNAL(processExited()),
                this, SLOT(scrollToTop()) );

        if ( !proc->start() ) {
            // error handling
            QMessageBox::critical( 0,
                    tr("Fatal error"),
                    tr("Could not start the uic command."),
                    tr("Quit") );
            exit( -1 );
        }
    }

    void UicManager::readFromStdout()
    {
        // Read and process the data.
        // Bear in mind that the data might be output in chunks.
        output->append( proc->readStdout() );
    }

    void UicManager::scrollToTop()
    {
        output->setContentsPos( 0, 0 );
    }

    int main( int argc, char **argv )
    {
        QApplication a( argc, argv );
        UicManager manager;
        a.setMainWidget( &manager );
        manager.show();
        return a.exec();
    }

    #include "process.moc"

See also QProcess Examples.