Home

A non-GUI example

This example shows how to use the single-application functionality in a console application. It does not require the QtGui library at all.

The only differences from the GUI application usage demonstrated in the other examples are:

1) The .pro file should include qtsinglecoreapplication.pri instead of qtsingleapplication.pri

2) The class name is QtSingleCoreApplication instead of QtSingleApplication.

3) No calls are made regarding window activation, for obvious reasons.

console.pro:

 TEMPLATE   = app
 CONFIG    += console
 SOURCES   += main.cpp
 include(../../src/qtsinglecoreapplication.pri)
 QT -= gui

main.cpp:

 /****************************************************************************
 **
 ** Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies).
 ** Contact: http://www.qt-project.org/legal
 **
 ** This file is part of the Qt Solutions component.
 **
 ** You may use this file under the terms of the BSD license as follows:
 **
 ** "Redistribution and use in source and binary forms, with or without
 ** modification, are permitted provided that the following conditions are
 ** met:
 **   * Redistributions of source code must retain the above copyright
 **     notice, this list of conditions and the following disclaimer.
 **   * Redistributions in binary form must reproduce the above copyright
 **     notice, this list of conditions and the following disclaimer in
 **     the documentation and/or other materials provided with the
 **     distribution.
 **   * Neither the name of Nokia Corporation and its Subsidiary(-ies) nor
 **     the names of its contributors may be used to endorse or promote
 **     products derived from this software without specific prior written
 **     permission.
 **
 ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 ** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 ** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 ** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 ** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 ** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 ** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 ** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 ** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
 **
 ****************************************************************************/

 #include "qtsinglecoreapplication.h"
 #include <QtCore/QDebug>

 void report(const QString& msg)
 {
     qDebug("[%i] %s", (int)QCoreApplication::applicationPid(), qPrintable(msg));
 }

 class MainClass : public QObject
 {
     Q_OBJECT
 public:
     MainClass()
         : QObject()
         {}

 public slots:
     void handleMessage(const QString& message)
         {
             report( "Message received: \"" + message + "\"");
         }
 };

 int main(int argc, char **argv)
 {
     report("Starting up");

     QtSingleCoreApplication app(argc, argv);

     if (app.isRunning()) {
         QString msg(QString("Hi master, I am %1.").arg(QCoreApplication::applicationPid()));
         bool sentok = app.sendMessage(msg, 2000);
         QString rep("Another instance is running, so I will exit.");
         rep += sentok ? " Message sent ok." : " Message sending failed; the other instance may be frozen.";
         report(rep);
         return 0;
     } else {
         report("No other instance is running; so I will.");
         MainClass mainObj;
         QObject::connect(&app, SIGNAL(messageReceived(const QString&)),
                          &mainObj, SLOT(handleMessage(const QString&)));
         return app.exec();
     }
 }

 #include "main.moc"