single instance process for Qt

qt.single.instance.cpp

// qt.single.instance.cpp
// 
// code from http://blog.naver.com/PostView.nhn?blogId=browniz1004&logNo=220957590867&categoryNo=15&parentCategoryNo=0&viewDate=&currentPage=8&postListTopCurrentPage=&from=postList&userTopListOpen=true&userTopListCount=5&userTopListManageOpen=false&userTopListCurrentPage=8

#include "mainwindow.h"
#include <QApplication>
#include <QSharedMemory> 

int main(int argc, char *argv[])
{    
  QApplication a(argc, argv);    
  MainWindow w;
  
  QSharedMemory shared("HelloWorld");    
  if(!shared.create(512,QSharedMemory::ReadWrite))    
  {        
    QMessageBox::information(&w,QObject::tr("HelloWorld"),QObject::tr("It's already running"),QMessageBox::Ok);        
    exit(0);    
  }
  
  w.show();
  return a.exec();
}