QT应用程序单实例运行

我们经常会做一些软件、程序只希望有最多一个运行实例。我从网上找到了个方法，虽然现在还不太明白原理，但是这种方法总算会用了。

原文摘自：http://dev.firnow.com/course/3_program/c++/cppxl/20100531/206675.html

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;
}

 当然别忘了在开头加上#include<QSharedMemory>

这段代码应该不用我多解释什么，虽然不太好理解，但是这段代码的用法对于QT入了门的人一目了然。