QApplication app = new QApplication(argc,argv);

对于的临时对象应该是QApplication app(argc,argv); 而不是QApplication app(argc,NULL);

如果是用到QDialog对象，必须保证QDialog在app前销毁

我使用argc = 0 ,argv=NULL 为啥不行，我这是在.so 中。不管有没有QDialog ，只有new 之后delete ,在主程序未退出之前再次调用那个函数，都会出错。

int ui_test(char *cmdstring,int argc, char **argv)
{
    // int argc=0;
    int ret = 0;
    if(!qApp){
        printf("kkkkkkkkkkkkkkkkkkkk\n");
        QApplication *app = new QApplication(argc, argv);
//        app->setQuitOnLastWindowClosed(true);
/*
        MYDialog * mydialog = new MYDialog();
        mydialog->show();
        mydialog->exec();
        delete  mydialog;
  */      //mydialog = NULL;
        delete app;
    } else {
        printf("#sleseee\n");
        MYDialog * mydialog = new MYDialog();
        mydialog->show();
        printf("#slxzxczxczxceseee\n");
        mydialog->exec();
        delete mydialog;
    }  
    return ret;
}

int main(int argc, char *argv[])
{   
    //  
    //QApplication app(argc,NULL);
    int i = 0;
    ui_test("ping 192.168.",argc,argv);
    printf("xxxx\n");
    ui_test("ping 192.168.",argc,argv);
    printf("xxxx###\n");
    ui_test("ping 192.168.",argc,argv);
    printf("xxxx###\n");
    //app.exec()
    //return a.exec();
    return 0;
}

QApplication::QApplication(int &argc, char **argv)
Initializes the window system and constructs an application object with argc command line arguments in argv.
Warning: The data referred to by argc and argv must stay valid for the entire lifetime of the QApplication object. In addition, argc must be greater than zero and argv must contain at least one valid character string.
The global qApp pointer refers to this application object. Only one application object should be created.
This application object must be constructed before any paint devices (including widgets, pixmaps, bitmaps etc.).
Note: argc and argv might be changed as Qt removes command line arguments that it recognizes.

这是官方文档关于QApplication的构造说明，注意Warning那段