如何获取当前QApplication？

#include <QApplication>
#include <QDebug>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    // 获取当前的 QApplication 实例
    QApplication *currentApp = qApp;
    qDebug() << "Current QApplication instance:" << currentApp;

    return app.exec();
}

#include <QApplication>
#include <QDebug>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    // 确保在 QApplication 实例创建之后调用 qApp
    QApplication *currentApp = qApp;
    if (currentApp) {
        qDebug() << "Current QApplication instance:" << currentApp;
    } else {
        qDebug() << "QApplication instance not found!";
    }

    return app.exec();
}

#include <QCoreApplication>
#include <QDebug>

int main(int argc, char *argv[])
{
    QCoreApplication coreApp(argc, argv);

    // 获取当前的 QCoreApplication 实例
    QCoreApplication *currentCoreApp = qApp;
    qDebug() << "Current QCoreApplication instance:" << currentCoreApp;

    return coreApp.exec();
}