When I use the following code, the output results of these are different. Only QDir outputs the information of exist. When I look at the source code, I find that it is set to the current path when its constructor is empty. The problem arises from the fact that I am still judged to exist when I use the function call passed in QDir to return null value. I think it is unreasonable for such interface design, although the current path will be used when the QDIR structure is empty is written in the official document.

QString getConfig() {
    return "";
}

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

    if (QDir(getConfig()).exists()) {
        qDebug() << "QDir exist";
    }
    if (QFile((getConfig())).exists()) {
        qDebug() << "QFile exist";
    }
    if (QFileInfo(getConfig()).exists()) {
        qDebug() << "QFileInfo exist";
    }

    return app.exec();
}