为什么接下来的两个代码序列表现不同？(Why do the next two code sequences behave differently?)

 我不明白为什么第一个代码序列创建一个QWidget元素重叠，而第二个代码序列行为正确。 唯一的区别是，在第一个中有一个QVBoxLayout指针，而在第二个中它是一个对象。 它是关于通过引用传递vs通过指针传递？ 我真的没有得到微妙的区别。 
 
 第一： 
 
QVBoxLayout vbox;
vbox.setSpacing(2);

QPushButton* quitButton = new QPushButton("Qsdfsuit");
QFont fnt = quitButton->font();
fnt.setPointSize(18);
fnt.setBold(true);
fnt.setFamily("Arial");
quitButton->setFont(fnt);

connect(quitButton, SIGNAL(clicked()), qApp, SLOT(quit()));

QLCDNumber* lcd = new QLCDNumber(2);

QSlider* slider = new QSlider(Qt::Horizontal);
slider->setRange(0, 99);
slider->setValue(0);

connect(slider, SIGNAL(valueChanged(int)), lcd, SLOT(display(int)));

vbox.addWidget(quitButton);
vbox.addWidget(lcd);
vbox.addWidget(slider);

this->setLayout(&vbox);
 
 第二个： 
 
QVBoxLayout* vbox = new QVBoxLayout();
vbox->setSpacing(2);

QPushButton* quitButton = new QPushButton("Qsdfsuit");
QFont fnt = quitButton->font();
fnt.setPointSize(18);
fnt.setBold(true);
fnt.setFamily("Arial");
quitButton->setFont(fnt);

connect(quitButton, SIGNAL(clicked()), qApp, SLOT(quit()));

QLCDNumber* lcd = new QLCDNumber(2);

QSlider* slider = new QSlider(Qt::Horizontal);
slider->setRange(0, 99);
slider->setValue(0);

connect(slider, SIGNAL(valueChanged(int)), lcd, SLOT(display(int)));

vbox->addWidget(quitButton);
vbox->addWidget(lcd);
vbox->addWidget(slider);

this->setLayout(vbox);

I don't understand why the first code sequence creates a QWidget where the elements overlap, while the second one behaves correctly. The only difference is that in the first one there is a QVBoxLayout pointer, while in the second one it's an object. It's about passing by reference vs passing by pointer? I really don't get the subtle difference.
 
First one:
 
QVBoxLayout vbox;
vbox.setSpacing(2);

QPushButton* quitButton = new QPushButton("Qsdfsuit");
QFont fnt = quitButton->font();
fnt.setPointSize(18);
fnt.setBold(true);
fnt.setFamily("Arial");
quitButton->setFont(fnt);

connect(quitButton, SIGNAL(clicked()), qApp, SLOT(quit()));

QLCDNumber* lcd = new QLCDNumber(2);

QSlider* slider = new QSlider(Qt::Horizontal);
slider->setRange(0, 99);
slider->setValue(0);

connect(slider, SIGNAL(valueChanged(int)), lcd, SLOT(display(int)));

vbox.addWidget(quitButton);
vbox.addWidget(lcd);
vbox.addWidget(slider);

this->setLayout(&vbox);
 
The second one:
 
QVBoxLayout* vbox = new QVBoxLayout();
vbox->setSpacing(2);

QPushButton* quitButton = new QPushButton("Qsdfsuit");
QFont fnt = quitButton->font();
fnt.setPointSize(18);
fnt.setBold(true);
fnt.setFamily("Arial");
quitButton->setFont(fnt);

connect(quitButton, SIGNAL(clicked()), qApp, SLOT(quit()));

QLCDNumber* lcd = new QLCDNumber(2);

QSlider* slider = new QSlider(Qt::Horizontal);
slider->setRange(0, 99);
slider->setValue(0);

connect(slider, SIGNAL(valueChanged(int)), lcd, SLOT(display(int)));

vbox->addWidget(quitButton);
vbox->addWidget(lcd);
vbox->addWidget(slider);

this->setLayout(vbox);

原文：https://stackoverflow.com/questions/26256518