QT应用程序单实例运行

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QSharedMemory *shareMem = new QSharedMemory(QString("SingleInstanceIdentify"));

    /* if the sharedmemory has not been created, it returns false, otherwise true.
     * But if the application exit unexpectedly, the sharedmemory will not detach.
     * So, we try twice.
     */

    volatile short i = 2;
    while (i--)
    {
        if (shareMem->attach(QSharedMemory::ReadOnly)) /* no need to lock, bcs it's read only */
        {
            shareMem->detach();
        }
    }

    if (shareMem->create(1))

    {
        MainWindow w;
        w.show();
        a.exec();
       
        if (shareMem->isAttached())
            shareMem->detach();
        delete shareMem;
    }

    return 0;
}